At various places we filter directory enumerations by inode type. Let's
add explicit support for that, so that the "struct dirent" array we
return already suppresses them.
This shortens code and makes things more robust.
This adds the following:
1. systemd-report gains a new --sign= option, taking a boolean. If true,
this makes systemd-report generate + systemd-report upload generate a
signed report, instead of a regular one. The signatures are collected
from Varlink-based backends.
2. One such backend is added which does a simple Ed21159 based signing
scheme.
3. this adds a new metrics source which just reports text files
symlinked into a special dir as metrics. This is used to report the
Ed21159 public key as metric, by default, if it exists.
4. finally, systemd-report itself is turned into a varlink service. this
is useful for example for extracting a report from a system coming in
via the varlink/http bridge.
I thought a long time about the format of signing of reports. Initially
i intended to do this like homed's user record signing, i.e. require
normalization of the record, then normalize the record, and write it out
in dense form, since the result. Finally insert the resulting hash into
the user record itself. People have pointed me to the inherent messiness
of signing JSON this way though, as it requires any participant that
wishes to sign/authenticate records this way to implement the exact same
normalization/formatting rules, and in particular in the area of
floating point numbers (of which metrics presumably will have many) this
is quite problematic.
This signing hence goes a different way. instead of expecting
signer+verifier to independently come to the same normalized text form
of the json data, let's instead output a JSON-SEQ sequence, where the
first object is the report, and any subsequent objects are one signature
each. the signatures are supposed to cover the precise binary
representation of the first element in the JSON-SEQ stream. (i.e. from
the RS to the NL).
or in other words: a verifier would receive the JSON-SEQ stream, split
it up before each RS. Then it would leave object 1 unparsed for the
moment, and parse objects 2…n. It would then authenticate object 1's
precise binary representation with objects 2…n. Once that checks out, it
would parse object 1, and use it as report.
The binary catalog reader trusted two values straight from a (possibly
hostile) database: open_mmap() summed header_size + n_items *
catalog_item_size in uint64 with no overflow check, and find_id() added
the matched item's offset to the map base with no upper bound. Reachable
through sd_journal_get_catalog() with $SYSTEMD_CATALOG set, this let
catalog_get()/catalog_list() strdup() a string starting outside the
mapping. Guard the size math with MUL_SAFE/INC_SAFE and reject item
offsets that fall outside the file.
These signatures can be provided by arbitrary Varlink backends symlinked
into /run/systemd/report/sign.
Also add a proper Varlink IDL for the upload interface, since we are
extended it now.
head_data_offset is declared as le64_t in journal-def.h, so it must be
assigned with htole64(p), not le64toh(p). All other le64_t field
assignments in this file (hash, next_hash_offset) consistently use
htole64().
On little-endian systems this makes no difference, but on big-endian
systems the field->data link would be stored with incorrect byte order,
corrupting journal file traversal.
Assisted-by: claude-opus-4-8 <noreply@anthropic.com>
When a slot is disconnected, previously we tried to remove the slot from
the hashmap with a wrong key. Hence, the pointer to the freed slot object
remained in the hashmap.
The cleanup destructor for VarlinkServerSocket only freed ss->address and
the struct, leaking ss->event_source. If sd_varlink_server_listen_address()
hits OOM at free_and_strdup() after the io-source was already armed, the
source stays registered in the event loop with userdata pointing at the
freed socket. Disable it before freeing; the call is a no-op when the
source was never armed, so the other freep sites are unaffected.
Follow-up for c14e841f31
Co-developed-by: Claude Opus 4.8 <noreply@anthropic.com>
When the accumulated trie key exceeds the fixed-size line buffer,
linebuf_get() returns NULL. trie_fnmatch_f() passed that NULL straight
into fnmatch() as the pattern, causing a SIGSEGV on a crafted hwdb.bin
(reachable now that recursion is capped rather than overflowing the
stack first). Treat the NULL like the other corruption checks and
return -EBADMSG.
Follow-up for 73fea38cf1
Fixes https://github.com/systemd/systemd/issues/42376
Co-developed-by: Claude Opus 4.8 <noreply@anthropic.com>
Many *at()-style helpers accept a directory fd that may be either a
regular, valid fd (>= 0) or one of the special AT_FDCWD/XAT_FDROOT
wildcard values, and open-code that check in their assertions. Add a
wildcard_fd_is_valid() helper for it and use it tree-wide.
Fixes a family of OOB reads in the trie walker where attacker-controlled
offsets are loaded from a (possibly hostile) hwdb.bin and added to
hwdb->map without first checking that the resulting pointer stays inside
the mapping. Crash sites:
- trie_fnmatch_f sd-hwdb.c:187 (#42340)
- trie_search_f sd-hwdb.c:233 (#42341)
- trie_children_cmp_f /bsearch sd-hwdb.c:94 (#42342)
- hwdb_add_property sd-hwdb.c:121 (#42343)
- trie_node_from_off (UBSAN) sd-hwdb.c:83
- trie_fnmatch_f stack overflow on cyclic children (CIFuzz finding)
Commit b45a897edc ("hwdb: reject out-of-bounds fnmatch prefixes")
plugged the first site only at the prefix_off-content level, but the
crash on the read of node->prefix_off itself still happens when node is
already OOB. This is the structural fix: a single hwdb_at() helper
validates that [off, off + size) lies inside the mapping, and
trie_node_from_off() / trie_string() return NULL on OOB; every caller
treats the result as nullable and surfaces -EBADMSG.
trie_fnmatch_f() additionally caps its recursion depth at 2048; without
the cap a corrupt trie whose child offsets form a cycle (or just a deep
linear chain) drives the parser into stack-overflow rather than
returning -EBADMSG (caught by CIFuzz address sanitizer on this branch).
Additions:
- A fuzz-hwdb libFuzzer harness that drives sd_hwdb_new_from_path,
sd_hwdb_get, sd_hwdb_seek, and sd_hwdb_enumerate on attacker bytes.
- Five hand-crafted unit tests in test-sd-hwdb.c (one per crash
bucket, plus the cyclic-trie recursion case) that build a malformed
in-memory hwdb.bin and assert -EBADMSG rather than SIGSEGV /
stack-overflow.
- Regression corpus files under test/fuzz/fuzz-hwdb/ pinning each
fixed bucket, including the CIFuzz stack-overflow reproducer.
Closes#42340.
Closes#42341.
Closes#42342.
Closes#42343.
Reported-by: AI-assisted libFuzzer campaign
Co-developed-by: Claude Opus 4.7 <noreply@anthropic.com>
Not the case on the sparc architecture. Replace with two translation
functions. The poll to epoll variant isn't used yet but will be used
when we add io-uring support to sd-event so we already add it here so
that it is in place.
Follow-up for cf4c65afa8
Ensure that fnmatch traversal doesn't go off the hwdb.bin in case of
a corrupted file
Originally reported on yeswehack.com as #YWH-PGM9780-70
For the unit test:
Co-developed-by: GitHub Copilot <github-copilot[bot]@users.noreply.github.com>
When a streaming method's callback returns 0 with no replies enqueued and
sd_varlink_set_sentinel() was passed NULL (POINTER_MAX), the framework
emits an empty parameters reply via sd_varlink_reply(v, NULL) as a clean
stream terminator. That call validated the empty parameters against the
method's output IDL — which always failed when the IDL declared any
mandatory output field, generating a spurious 'didn't pass validation'
warning even though the empty terminator is correct by construction.
Move the body of sd_varlink_reply() into a static varlink_reply_internal()
that takes a skip_validation flag. The public sd_varlink_reply() keeps
its existing behavior (validation enabled). Add a static
varlink_reply_terminator() helper that wraps
varlink_reply_internal(v, NULL, /* skip_validation= */ true), and route
varlink_dispatch_sentinel() through it for the synthetic empty terminator,
so both the synchronous dispatch path (varlink_dispatch_method()) and the
fiber path (varlink_fiber_entry()) skip validation in one place.
Without this, callers who want 'streaming method, possibly empty result'
semantics had to either fire a logically wrong 'NotFound'-style error
sentinel on empty (sysext.List, BootControl.ListBootEntries pattern) or
mark every output field NULLABLE just to placate the validator (the
io.systemd.Manager.EnqueueMarkedJobs approach), misrepresenting the
contract — exactly the tradeoff the FIXME in pcrlock.c flagged. With
this change, the empty terminator is invisible to the IDL validator and
the FIXME is no longer needed.
Co-developed-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Traditionally, asynchronous programming in systemd has been achieved
using
sd-event along with the asynchronous interfaces of sd-bus and
sd-varlink.
This works well when the system is reacting to events and all code
triggered
by those events can run without blocking. In these scenarios, the global
Manager object is passed as userdata to the callback, and the callback
can
use the stack as usual, declaring local state and ensuring proper
cleanup via
_cleanup_. Control flow structures, such as loops, work as expected, and
everything runs smoothly.
However, challenges arise when the code needs to perform long-running
operations within these callbacks. Since the system cannot block
execution
within the callback, we can't directly invoke a long-running operation
and
wait for its result without introducing complexities. Instead, we need
to
initiate the long-running task, register for completion with sd-event,
sd-bus, or sd-varlink, and provide a callback to be invoked when the
operation completes.
This callback, however, only receives a single userdata pointer, which
forces us to bundle all local variables into a struct and pass it along
as
part of the callback. On top of that, after queuing the asynchronous
operation, the caller continues executing. As the caller's stack unwinds
when the function exits, the resources and state within the local scope
may
be prematurely cleaned up. Therefore, the struct must store copies of
the
local variables or ensure proper reference counting to prevent premature
resource cleanup.
When multiple long-running operations need to be initiated within a
loop,
the complexity grows further. We must introduce additional shared state
to
track the completion of all operations before we can run any code that
depends on their results.
Furthermore, since the daemon may be shut down at any time, we must
track
the lifecycle of each long-running operation in the global Manager
struct,
ensuring proper cleanup even when stack unwinding can no longer manage
the
resources for us.
Fibers, or green threads, provide a more natural way of handling
asynchronous operations. By enabling cooperative multitasking within a
single thread, fibers allow us to write code that looks like it’s
running
synchronously, but with the ability to yield control at predefined
points,
such as when waiting for long-running tasks to complete.
With fibers, we can simplify the control flow by running asynchronous
operations within a fiber, allowing us to "pause" execution while
waiting
for the long-running operation to finish and then "resume" the operation
once
it's complete. This eliminates the need for multiple callback chains,
extensive state tracking, and the potential pitfalls of stack unwinding.
This commit introduces the ability to execute long-running operations in
a
non-blocking manner while maintaining the simplicity and readability of
synchronous code. The fiber-based approach will significantly improve
the
handling of complex workflows, making the code easier to write and
maintain.
The implementation is based on ucontext.h's makecontext() (with a
fallback
to the venerable sigaltstack() approach on musl),
sigsetjmp()/siglongjmp()
and sd-event. ucontext.h provides us with alternate stacks that we can
switch
between. We use sigsetjmp()/siglongjmp() instead of swapcontext()
because the
latter forcibly saves/restores a per context signal mask every time it
is called.
Using sigsetjmp()/siglongjmp(), we can avoid the unnecessary syscall and
maintain
a per thread signal mask, which makes much more sense than having a per
fiber
signal mask.
The default stack size is the same as a regular thread. Because we
use mmap() to allocate the stack, the memory won't actually be used
until it
is paged in by the kernel, so we don't actually use 8MB per fiber.
To integrate fibers with the event loop, each fiber is assigned a
deferred
event source which resumes the fiber when enabled. The deferred event
source
is oneshot by default so the fiber will run immediately until it yields
or
suspends. If it yields, the deferred event source is enabled again
(oneshot)
immediately. If it suspends, before it suspends, one or more event
sources
are registered with sd-event that will enable the deferred event source
(oneshot) to resume the fiber once the operation it is waiting for
completes.
Yielding or suspending the fiber is done by calling sd_fiber_yield() or
sd_fiber_suspend() respectively. Both of these return zero on success or
any
error value from the async operation that caused the fiber to resume.
This is also how fiber cancellation is implemented. When a fiber is
cancelled,
sd_fiber_yield() and sd_fiber_suspend() will return ECANCELED when the
fiber
is resumed, allowing the fiber to unwind its stack (which allows cleanup
to
happen automatically) and finish.
Instead of having applications work directly with fibers, we hide them
behind
a generic futures interface to represent long-running operations,
regardless of
whether those operations are running on a fiber or not. Aside from
fibers, the
futures library (sd-future) will for example allow waiting for sd-event
sources
and doing sd-bus calls in the background as well. Fibers can suspend
until a
future is ready with sd_fiber_await() or by having the future wake up
the fiber
explicitly in its callback. A future always defaults to waking up the
current
fiber.
Each future kind plugs into the library by providing an sd_future_ops
vtable
(alloc, free, cancel, set_priority). The library treats the impl pointer
returned by alloc() as a black box. Future Implementations retrieve it
via
sd_future_get_private().
A future starts in SD_FUTURE_PENDING and transitions exactly once to
SD_FUTURE_RESOLVED, carrying an integer result. Consumers can react to
that
transition either by installing a one-shot callback with
sd_future_set_callback() (callback-style code) or by waiting on it from
a
fiber via sd_fiber_await() (synchronous-looking fiber code).
sd_fiber_await()
is itself built on a "wait future" that resolves when its target
resolves;
sd_future_new_wait() exposes the same primitive directly so non-fiber
callers
can chain futures without involving a fiber.
Cancellation is cooperative: sd_future_cancel() invokes the future
impl's
cancel callback, which is responsible for tearing down its work and
ultimately
resolving the promise with -ECANCELED. For fiber futures this is what
surfaces as the ECANCELED return from
sd_fiber_yield()/sd_fiber_suspend()
mentioned above.
Fire-and-forget fibers — created by passing a NULL ret to sd_fiber_new()
—
take a self-reference on their future so they outlive the caller's
scope.
The self-ref is dropped when the fiber resolves. This floating mechanism
(sd_fiber_set_floating()) is restricted to fiber futures because they
uniquely guarantee resolution; allowing it for arbitrary future kinds
would
risk silent leaks for kinds that may never resolve.
Note that fiber cleanup depends on the runtime operating normally. Each
fiber's _cleanup_-style cleanups live on the fiber's own stack and run
only when the fiber is resumed and allowed to unwind, which requires a
working event loop to drive it to completion. The exit event source
registered for top-level fibers ensures unwind on a normal
sd_event_exit(),
but if the event loop itself terminates abnormally (e.g. an
unrecoverable
allocation failure mid-dispatch) before all fibers have resolved, their
stacks never unwind and any resources they own leak.
The code lives in libsystemd as sd-future (not exported) for the
following reasons:
- We may want to make this a public libsystemd API in the future
- The code can't live in src/basic as it makes heavy use of sd-event
- The code can't live in src/shared as sd-bus and sd-event make use of
it
The log and log-context headers are updated with functions to allow
fibers to have their own log prefix and log context.
Add varlink_server_bind_fiber() and varlink_server_bind_fiber_many()
in varlink-util.{c,h} for registering a method handler that should
run on a dedicated fiber per dispatch. The fiber-bound methods live
in a separate s->fiber_methods map alongside the regular s->methods;
bind_internal()/bind_many_internal() are factored out so the regular
and fiber bind variants share their parsing/insertion code.
Registering the same method in both maps is rejected because the
dispatcher consults the regular map first and would otherwise
silently shadow the fiber binding.
varlink_dispatch_fiber() builds a VarlinkFiberData (refs to the
connection, parameters, and method name), spawns a fiber via
sd_fiber_new(), and makes the future floating so the fiber
self-manages its lifetime — neither the dispatcher nor the
connection has to track it. The fiber's priority is set to one
below the connection's quit event source so that on graceful
shutdown the fiber's exit handler fires (and runs its cleanup)
before varlink's quit_callback() closes the connection underneath
it; this is what lets a fiber-bound handler reply or flush its
sentinel on a still-open connection during shutdown.
The connection state transitions are reordered so they happen before
the fiber spawn rather than after the synchronous callback returns:
the fiber runs after dispatch has already moved past PROCESSING, which
matches the behaviour expected for a deferred reply (the fiber may
either reply immediately, or stash the connection and reply later, in
which case the post-callback logic treats it as a PENDING_METHOD).
Note that all the synchronous varlink APIs (sd_varlink_call() and friends)
already behave properly when on a fiber because they call json_stream_wait()
which calls ppoll_usec() which we already fixed to suspend when called from
a fiber.
The client/server varlink tests are migrated to fibers (threads → mock
server fibers on the same event loop) to exercise the new paths.
Two changes to teach sd-bus how to behave when called from a fiber, in
order of increasing depth:
2. sd_bus_call() now redirects to a new bus_call_suspend() helper when
the caller is a fiber whose event loop is the same one the bus is
attached to. The plain bus_poll() path serializes all bus traffic on
the slot's reply (only one method call can be in flight per
sd_bus*), which would defeat the point of running multiple fibers
against one bus. bus_call_suspend() builds on the async sd-bus API:
it wraps the call in a new BusFuture (sd-bus/bus-future.{c,h}) that
resolves when the reply or method-error arrives, lets the fiber
await that future, and surfaces the reply to the caller via
future_get_bus_reply(). Because the futures live on the event loop
rather than a per-bus slot, multiple fibers can drive concurrent
method calls against the same bus.
3. A new private SD_BUS_VTABLE_METHOD_FIBER flag dispatches a vtable
method handler on its own fiber, so handlers are free to use
sd_bus_call() against the same bus, sd_fiber_sleep(), loop_read(),
etc. without stalling the event loop for other connections or
handlers. The flag stays out of sd-bus-vtable.h (its bit value is
reserved there to prevent collisions) — the fiber runtime is a
systemd-internal implementation detail.
Lifecycle of fiber-dispatched handlers is tracked on the bus itself: a
new bus->fiber_futures set holds a ref to each in-flight handler.
bus_enter_closing() cancels every entry and process_closing() returns
with the bus still in CLOSING state until the set drains, so we can be
sure no fiber handler outlives the bus. bus_fiber_resolved() removes
the entry on completion. bus_free()'s assert(set_isempty()) makes the
invariant load-bearing.
Note that plain sd_bus_call() already works correctly on a fiber as it
calls ppoll_usec() which has already been modified to suspend when
running on a fiber.
To exercise these changes the existing thread-based client/server
sd-bus tests (test-bus-chat, test-bus-objects, test-bus-peersockaddr,
test-bus-server, test-bus-watch-bind) are migrated to fibers, and a
new test-bus-fiber is added that covers SD_BUS_VTABLE_METHOD_FIBER —
including handlers that issue nested sd_bus_call() on the same bus, the
cancel-on-close path, and concurrent dispatches across multiple fibers.
sd_event_run() blocks the calling thread on the event loop's epoll fd
until something happens. When the caller is a fiber, that's the wrong
behaviour: blocking the thread also stalls every other fiber and the
outer event loop driving them. The most common way to hit this is a
fiber that creates its own inner event loop (e.g. a server-style fiber
that wants to dispatch its own sources independently of whatever loop
the test or supervising fiber is running on) — with the existing
implementation the inner sd_event_run() would hold the thread while the
outer scheduler should be free to advance other fibers.
Add an event_run_suspend() variant in sd-event/event-future.c that
performs the same prepare/wait/dispatch dance, but when the fast path
finds nothing ready it (a) creates an IO future watching the inner
event loop's epoll fd on the *outer* event loop, (b) optionally creates
a time future for the timeout, and (c) suspends the fiber. When either
future fires the fiber is resumed and the prepare/wait/dispatch sequence
runs once more to actually dispatch what's pending. sd_event_run()
checks sd_fiber_is_running() and delegates to this variant when on a
fiber; profile_delays accounting is intentionally skipped on that path
since the underlying prepare/wait/dispatch primitives already account
for themselves.
Some helpers in src/basic — ppoll_usec_full() (used by fd_wait_for_event()),
loop_read(), loop_read_exact(), loop_write_full() and
pidref_wait_for_terminate_full() — block the calling thread. That's the
right behaviour outside a fiber but not inside one, where blocking the
thread also stalls every other fiber running on the same event loop.
Rewriting every caller to pick a fiber or non-fiber variant explicitly
would be a lot of churn and would split otherwise-shared code paths in
two.
Instead, the helpers detect at runtime whether they're running on a fiber
and dispatch to a suspending variant when they are. FiberOps in
fiber-ops.h holds five function pointers (ppoll, read, write, timeout,
cancel_wait_unref); a fiber_ops global constant is populated whenever we
enter a fiber with functions that delegate to suspending variants of common
syscalls. With this approach, the variants themselves stay in libsystemd
which is required because they make use of sd-event.
- loop_read()/loop_read_exact() take the fiber read hook on a fiber
unless the caller asked for a non-blocking attempt (do_poll=false) and
the fd is already non-blocking — in that case we fall through to read()
to preserve the existing return-EAGAIN-immediately semantic. The hook
itself suspends on EAGAIN until data is available, so neither the
do_poll knob nor the explicit fd_wait_for_event() retry loop are
needed on the fiber path.
- loop_write_full() likewise takes the fiber write hook on a fiber,
except when timeout=0 with an already-non-blocking fd (preserving the
fast-return-EAGAIN semantic). The fiber path runs inside a
FIBER_OPS_TIMEOUT() scope so the caller's timeout is honoured via a
deadline future, mirroring SD_FIBER_TIMEOUT() but reachable from
src/basic without pulling in sd-future.h.
- pidref_wait_for_terminate_full() polls the pidfd via fd_wait_for_event()
before each waitid() when either a finite timeout is set or we're on a
fiber, and requires pidref->fd >= 0 in those cases (returning
-ENOMEDIUM otherwise — extending the rule that already applied to
finite timeouts). The poll suspends the fiber via the ppoll hook above;
the subsequent waitid() doesn't block because the pidfd is already
signalled.
Add a family of sd_fiber_*() I/O wrappers that, when called from a
fiber, behave like blocking I/O from the caller's perspective but
yield to the event loop instead of blocking the thread:
sd_fiber_read / sd_fiber_write
sd_fiber_readv / sd_fiber_writev
sd_fiber_recv / sd_fiber_send
sd_fiber_connect
sd_fiber_recvmsg / sd_fiber_sendmsg
sd_fiber_recvfrom / sd_fiber_sendto
sd_fiber_accept
sd_fiber_ppoll
Most of them share a single helper, fiber_io_operation(), which when
invoked outside a fiber falls through to the underlying syscall
directly, preserving the regular blocking behaviour. Inside a fiber
the helper flips the fd to non-blocking (restoring its original mode
on return), tries the syscall once on the fast path, and on EAGAIN/
EWOULDBLOCK creates an sd-event-backed IO future via future_new_io(),
suspends the fiber, and retries the syscall once the event source
fires.
future_new_io() itself is added to sd-event/event-future.{c,h} as a
new IoFuture kind. It wraps sd_event_add_io() into an sd_future:
oneshot enable, EPOLLERR translated via SO_ERROR (suppressed for
non-sockets), and the fd duplicated with F_DUPFD_CLOEXEC to avoid
EEXIST when multiple sources watch the same descriptor.
Together these let fiber-using code write straight-line socket and
pipe I/O without bundling state into callbacks.
Traditionally, asynchronous programming in systemd has been achieved using
sd-event along with the asynchronous interfaces of sd-bus and sd-varlink.
This works well when the system is reacting to events and all code triggered
by those events can run without blocking. In these scenarios, the global
Manager object is passed as userdata to the callback, and the callback can
use the stack as usual, declaring local state and ensuring proper cleanup via
_cleanup_. Control flow structures, such as loops, work as expected, and
everything runs smoothly.
However, challenges arise when the code needs to perform long-running
operations within these callbacks. Since the system cannot block execution
within the callback, we can't directly invoke a long-running operation and
wait for its result without introducing complexities. Instead, we need to
initiate the long-running task, register for completion with sd-event,
sd-bus, or sd-varlink, and provide a callback to be invoked when the
operation completes.
This callback, however, only receives a single userdata pointer, which
forces us to bundle all local variables into a struct and pass it along as
part of the callback. On top of that, after queuing the asynchronous
operation, the caller continues executing. As the caller's stack unwinds
when the function exits, the resources and state within the local scope may
be prematurely cleaned up. Therefore, the struct must store copies of the
local variables or ensure proper reference counting to prevent premature
resource cleanup.
When multiple long-running operations need to be initiated within a loop,
the complexity grows further. We must introduce additional shared state to
track the completion of all operations before we can run any code that
depends on their results.
Furthermore, since the daemon may be shut down at any time, we must track
the lifecycle of each long-running operation in the global Manager struct,
ensuring proper cleanup even when stack unwinding can no longer manage the
resources for us.
Fibers, or green threads, provide a more natural way of handling
asynchronous operations. By enabling cooperative multitasking within a
single thread, fibers allow us to write code that looks like it’s running
synchronously, but with the ability to yield control at predefined points,
such as when waiting for long-running tasks to complete.
With fibers, we can simplify the control flow by running asynchronous
operations within a fiber, allowing us to "pause" execution while waiting
for the long-running operation to finish and then "resume" the operation once
it's complete. This eliminates the need for multiple callback chains,
extensive state tracking, and the potential pitfalls of stack unwinding.
This commit introduces the ability to execute long-running operations in a
non-blocking manner while maintaining the simplicity and readability of
synchronous code. The fiber-based approach will significantly improve the
handling of complex workflows, making the code easier to write and maintain.
The implementation is based on ucontext.h's makecontext() (with a fallback
to the venerable sigaltstack() approach on musl), sigsetjmp()/siglongjmp()
and sd-event. ucontext.h provides us with alternate stacks that we can switch
between. We use sigsetjmp()/siglongjmp() instead of swapcontext() because the
latter forcibly saves/restores a per context signal mask every time it is called.
Using sigsetjmp()/siglongjmp(), we can avoid the unnecessary syscall and maintain
a per thread signal mask, which makes much more sense than having a per fiber
signal mask.
The default stack size is the same as a regular thread. Because we
use mmap() to allocate the stack, the memory won't actually be used until it
is paged in by the kernel, so we don't actually use 8MB per fiber.
To integrate fibers with the event loop, each fiber is assigned a deferred
event source which resumes the fiber when enabled. The deferred event source
is oneshot by default so the fiber will run immediately until it yields or
suspends. If it yields, the deferred event source is enabled again (oneshot)
immediately. If it suspends, before it suspends, one or more event sources
are registered with sd-event that will enable the deferred event source
(oneshot) to resume the fiber once the operation it is waiting for completes.
Yielding or suspending the fiber is done by calling sd_fiber_yield() or
sd_fiber_suspend() respectively. Both of these return zero on success or any
error value from the async operation that caused the fiber to resume.
This is also how fiber cancellation is implemented. When a fiber is cancelled,
sd_fiber_yield() and sd_fiber_suspend() will return ECANCELED when the fiber
is resumed, allowing the fiber to unwind its stack (which allows cleanup to
happen automatically) and finish.
Instead of having applications work directly with fibers, we hide them behind
a generic futures interface to represent long-running operations, regardless of
whether those operations are running on a fiber or not. Aside from fibers, the
futures library (sd-future) will for example allow waiting for sd-event sources
and doing sd-bus calls in the background as well. Fibers can suspend until a
future is ready with sd_fiber_await() or by having the future wake up the fiber
explicitly in its callback. A future always defaults to waking up the current
fiber.
Each future kind plugs into the library by providing an sd_future_ops vtable
(alloc, free, cancel, set_priority). The library treats the impl pointer
returned by alloc() as a black box. Future Implementations retrieve it via
sd_future_get_private().
A future starts in SD_FUTURE_PENDING and transitions exactly once to
SD_FUTURE_RESOLVED, carrying an integer result. Consumers can react to that
transition either by installing a one-shot callback with
sd_future_set_callback() (callback-style code) or by waiting on it from a
fiber via sd_fiber_await() (synchronous-looking fiber code). sd_fiber_await()
is itself built on a "wait future" that resolves when its target resolves;
sd_future_new_wait() exposes the same primitive directly so non-fiber callers
can chain futures without involving a fiber.
Cancellation is cooperative: sd_future_cancel() invokes the future impl's
cancel callback, which is responsible for tearing down its work and ultimately
resolving the promise with -ECANCELED. For fiber futures this is what
surfaces as the ECANCELED return from sd_fiber_yield()/sd_fiber_suspend()
mentioned above.
Fire-and-forget fibers — created by passing a NULL ret to sd_fiber_new() —
take a self-reference on their future so they outlive the caller's scope.
The self-ref is dropped when the fiber resolves. This floating mechanism
(sd_fiber_set_floating()) is restricted to fiber futures because they
uniquely guarantee resolution; allowing it for arbitrary future kinds would
risk silent leaks for kinds that may never resolve.
Note that fiber cleanup depends on the runtime operating normally. Each
fiber's _cleanup_-style cleanups live on the fiber's own stack and run
only when the fiber is resumed and allowed to unwind, which requires a
working event loop to drive it to completion. The exit event source
registered for top-level fibers ensures unwind on a normal sd_event_exit(),
but if the event loop itself terminates abnormally (e.g. an unrecoverable
allocation failure mid-dispatch) before all fibers have resolved, their
stacks never unwind and any resources they own leak.
The code lives in libsystemd as sd-future (not exported) for the following reasons:
- We may want to make this a public libsystemd API in the future
- The code can't live in src/basic as it makes heavy use of sd-event
- The code can't live in src/shared as sd-bus and sd-event make use of it
The log and log-context headers are updated with functions to allow
fibers to have their own log prefix and log context.
Previously, sd-dhcp-server can be run as a DHCP relay agent.
But, DHCP server and DHCP relay agent behave completely differently,
hence there is almost no code that can be shared between the two modes.
Let's split out the DHCP relay agent feature from sd-dhcp-server.
The new DHCP relay agent supports:
- multiple upstream and downstream interfaces,
- gateway address (giaddr field in DHCP message header) is configurable,
- supports more DHCP relay agent information sub-options,
- each interface has their own socket fd, and each socket is bound to
the interface, so that we can enable/disable each interface
safely without affecting other interfaces, and we can filter out any
unexpected packets from unmanaged interfaces,
networkd integration and test cases will be added later.
Drop the -fundamental suffix from src/fundamental/ headers in favor of names
that match their src/basic/ or src/shared/ counterparts (e.g.
macro-fundamental.h -> macro.h, assert-fundamental.h -> assert-util.h,
cleanup-fundamental.h -> cleanup-util.h). Rename src/basic/{btrfs,label}.{c,h}
to use the -util suffix to match the existing shared/btrfs-util and
shared/label-util siblings. Rename src/shared/mkdir-label.{c,h} to mkdir.{c,h}
and src/shared/tmpfile-util-label.{c,h} to tmpfile-util.{c,h} to match the
corresponding src/basic names.
This saves us from having to come up with separate names for files that do
the same thing across tiers, and it makes it easier to move stuff between
src/fundamental, src/basic and src/shared: consumers just #include "foo.h"
and pick up whichever tier their -I path resolves to first, so call sites
don't need to be updated when an API moves between layers.
Where a higher-tier wrapper exists (e.g. src/basic/macro.h wrapping
src/fundamental/macro.h), the wrapper uses an explicit "../fundamental/foo.h"
or "../basic/foo.h" relative include for the lower-tier header. We can't use
GCC's #include_next directive for this — when the wrapper is reachable both
via same-dir-as-source lookup and via -I (e.g. -Isrc/shared) for the
directory it lives in, #include_next advances by exactly one slot in libcpp's
internal directory chain and lands on the same physical directory it was
already in, never reaching the lower-tier sibling (see make_cpp_dir() in
gcc/libcpp/files.cc:1986).
To make sure the right headers are always picked up, the include directories
are reordered so that e.g. src/shared always takes priority over src/basic and
similar for the other directories.
Co-developed-by: Claude Opus 4.7 <noreply@anthropic.com>
- test-random-util is reworked to not use sqrt()
- pretty-print.c inlines ceil() so libm doesn't have
to be linked into libshared
- We add fno-math-errno to allow inlining of more math
functions by not requiring standard math functions to
set errno on invalid input.
exp10() has a symbol version > 2.34 on latest glibc. To allow
dropping our baseline required glibc runtime version to <= 2.34,
let's add our own version to prevent pulling in the newer symbol
from glibc.
Methods:
- `io.systemd.Job.List` — list all queued jobs or look up by `id`/`unit`
name, with streaming support. Uses context/runtime split: `JobContext`
(Unit, JobType) and `JobRuntime` (Id, State, Result,
ActivationDetails). Follows the same SELinux and parameter-conflict
patterns as `io.systemd.Unit.List`.
- `io.systemd.Job.Cancel` — cancel a specific job by ID, with SELinux
and polkit authorization.
- `io.systemd.Job.ClearAll` — cancel all pending jobs, with SELinux and
polkit authorization.
`message_skip_fields()` recursively processes D-Bus variant types in
message header fields with no depth limit. A crafted message with deeply
nested variants can cause unbounded recursion and overflow the stack.
Add a `depth` parameter checked against `BUS_CONTAINER_DEPTH` (128),
matching the limit already enforced by the public
`sd_bus_message_skip()` API. All recursive call sites pass `depth + 1`,
and the top-level caller in `message_parse_fields()` passes `0`.
Craft a raw D-Bus message with an unknown header field containing
BUS_CONTAINER_DEPTH+1 nested variants and verify that message parsing
rejects it with -EBADMSG rather than recursing until stack overflow.
message_skip_fields() recurses for each nested variant ('v') type in
D-Bus message header fields. A crafted message with deeply nested
variants (e.g., a variant containing a variant containing a variant...)
causes unbounded stack growth, leading to stack overflow and crash.
Add a depth parameter that increments on each recursive call and
rejects messages exceeding BUS_CONTAINER_DEPTH with -EBADMSG. This
matches the existing depth limits enforced elsewhere in the sd-bus
message processing (e.g., bus_message_enter_container).
Each dlopen_*() wrapper kept its dl handle as a file-scope
'static void *xxx_dl = NULL;' even though only the wrapper itself
ever referenced it. Move each one inside the corresponding function
so its scope matches its actual use, leaving the rest of each
translation unit free of the unused file-scope name.
In pcre2-util.c the assert(pcre2_dl) in pattern_matches_and_log()
becomes assert(sym_pcre2_match), which carries the same invariant
(pattern_compile_and_log() ran dlopen_pcre2()).
- **bpf-util: rename from bpf-dlopen, unify version-specific symbol
handling**
- **cryptsetup: dlopen libcryptsetup in tokens**
- **tree-wide: dlopen libpam in pam plugins**
- **test-bus-marshal: dlopen() glib and libdbus instead of linking
directly**
- **lock-util: Simplify timeout for lock_generic_with_timeout()**
- **color-util: simplify hsv_to_rgb, fix rgb_to_hsv negative-hue wrap**
- **tree-wide: Use our own macros instead of fabs()/fmax()/fmin()**
- **locale-util: dlopen() libintl instead of linking against it**
- **home: Use log2u64() over log2()**
- **meson: drop libdl, threads, and librt dependencies**
- **libc: Use dlsym() from a constructor instead of weak symbols**
- **libc: Make sure C23 versions of strtol(), sscanf() are not used**
Our baseline glibc is 2.34, which merged libdl, libpthread (the
dependency('threads') target), and librt into libc. Empty .so/.a stubs
remain for backward compatibility with old binaries, but new builds
resolve dl_*, pthread_*, mq_*, timer_*, etc. directly from libc.
On musl the same libraries are likewise empty stubs.
Drop the libdl, threads, and librt entries from every meson.build, and
remove the now-stale 'Libs.private: -lrt -pthread' from libudev.pc.in
since both flags resolve to empty link-time stubs on glibc 2.34+ and
musl.
Verified with readelf -d that libsystemd.so, libudev.so, and systemd no
longer carry DT_NEEDED entries for libdl/libpthread/librt.
To make this work, ABS() is made generic so it also works on
floats and doubles.
While at it, fold the __ABS_INTEGER indirection and the
assert_cc(sizeof(long long) == sizeof(intmax_t)) away. The previous
form switched between __builtin_llabs (clang) and __builtin_imaxabs
(gcc), with the assert keeping the two paths behaviorally identical
on every platform we build for. imaxabs was originally chosen because
intmax_t is conceptually the widest signed integer type the platform
exposes, but the _Generic ABS already casts to (long long) before the
call, so the extra width imaxabs could in theory carry was being
narrowed away immediately anyway. With both paths collapsed to
__builtin_llabs((long long) (a)), the size relationship between
long long and intmax_t is no longer relevant.
Also add explicit unsigned long long / unsigned long / unsigned int
cases that pass the argument through unchanged. The previous default
branch cast unsigned values to (long long); for values above LLONG_MAX
this reinterprets them as negative, and __builtin_llabs(LLONG_MIN) is
UB. Unsigned values are already non-negative, so passing them through
is both correct and avoids the narrowing. Smaller unsigned types
(unsigned char, unsigned short) still go through the default branch
but promote to int first and fit in long long losslessly.
Co-developed-by: Claude Opus 4.7 <noreply@anthropic.com>
The test only uses 9 symbols (5 from glib, 4 from libdbus) for its
interop checks; dlopen them at runtime so the binary no longer carries a
hard link-time dependency on either library. Headers are still pulled in
through the *_cflags partial dependencies for the type declarations.
While we're at it, drop the compat glue for glib 2.36 which is long obsolete
at this point.
Job IDs are uint32_t values that are always >= 1 (the manager's ID counter starts at 1 and wraps from UINT32_MAX back to 1, never assigning 0). Add a dedicated dispatch function that validates this constraint, rejecting 0 and treating null as "unset" (0).
Co-developed-by: Claude Opus 4.6 <noreply@anthropic.com>
Lennart Poettering
jmestwa-coder
Mike Yuan
dongshengyuan
Yu Watanabe
Luca Boccassi
jeffhuang
Zbigniew Jędrzejewski-Szmek
Daan De Meyer
Yaping Li
TristanInSec
Ivan Kruglov