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.
terminal_get_size() writes ANSI escape sequences (CSI 18 and DSR
queries) to the output fd to determine terminal dimensions. This is
called during early boot via reset_dev_console_fd() and from service
execution contexts via exec_context_apply_tty_size().
Previously, these writes used loop_write() on a blocking fd, which
could block indefinitely if the terminal is not consuming data — for
example on a serial console with flow control asserted, or a
disconnected terminal. This is the same problem that was solved for
terminal_reset_ansi_seq() in systemd/systemd#32369 by temporarily
setting the fd to non-blocking mode with a write timeout.
Apply the same pattern here: set the output fd to non-blocking in
terminal_get_size() before issuing the queries, and restore blocking
mode afterward. Change the loop_write() calls in
terminal_query_size_by_dsr() and terminal_query_size_by_csi18() to
loop_write_full() with a 100ms timeout so writes fail gracefully
instead of hanging.
Also introduce the CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC constant for all
timeouts used across all ANSI sequence writes and reads (vt_disallocate(),
terminal_reset_ansi_seq(), and the two size query functions). 333ms
is now used for all timeouts in terminal-util.c.
Also introduce a cleanup function for resetting a fd back to blocking
mode after it was made non-blocking.
The old name suggested this would only check if the two inodes are on
the same mount, but it actually checks if they are the same inodes too.
Let's rename it to make this clearer, in particular as we have
both statx_inode_same() and statx_mount_same() already, and they are
even used here, and hence very confusing.
This also drops two checks from the test case, which are simply wrong.
Given they apparently weren't load bearing (since no CI tripped up),
let's just drop them.
This takes inspiration from AT_FDCWD, but always references the root dir
rather than the cwd. This allows various convenience uses, as we can now
reference the root dir without actually allocating an fd for chaseat(),
fd_get_path() and various others.
The value of XAT_FDROOT is chosen so that it is not a valid fd (essential,
because we do not intend to hook this up everywhere, just where we need
it, just like AT_FCWD only works in some syscalls), and we want uses at
the wrong places to fail cleanly. It also uses a valud outside of the
range where we usually return negative errnos, i.e. < -ERRNO_MAX.
This checks whether a file descriptor is valid and opened in a mode that
allows writing (O_WRONLY or O_RDWR). This is useful when we want to
verify that inherited FDs can actually be used for output operations
before dup'ing them.
The helper explicitly handles O_PATH file descriptors, which cannot be
used for I/O operations and thus are never writable.
Let's not leak details from src/shared and src/libsystemd into
src/basic, even though you can't actually do anything useful with
just forward declarations from src/shared.
The sd-forward.h header is put in src/libsystemd/sd-common as we
don't have a directory for shared internal headers for libsystemd
yet.
Let's also rename forward.h to basic-forward.h to keep things
self-explanatory.
- use unsigned for the return value of read_nr_open(), as it does not
fail, and the kernel internally uses unsigned for the value,
- when bumping the value by PID1, let's start from the kernel's maximum
value defined in fs/file.c. The maximum value should be mostly an API
of the kernel, but may changed in a future, hence still try several
times if we fail to bump the value.
Co-authored-by: Jared Baur <jaredbaur@fastmail.com>
Co-authored-by: John Rinehart <johnrichardrinehart@gmail.com>
We're still discussing whether we want to remove this or not, but
regardless of whether we end up removing it or not, it's something
we add ourselves and as such should not live in our headers that
override glibc headers, so let's move it to fd-util.h.
This is not something that comes from glibc, but which we invent
ourselves. As such, it should not be part of our overrides of glibc
headers, but instead should be part of one of our own headers, so
let's move it to fd-util.h.
Follow up for 194a690181
Let's keep macro.h for the extremely generic macros that don't fit anywhere
else. Since CLEANUP_ARRAY() is already in memory-util-fundamental.h, we can
make a good case for moving the other cleanup macros in there as well.
Currently, if proc_mounted() != 0, some functions
propagate -ENOENT while others return -EBADF.
Let's make things consistent, by introducing
a static inline helper responsible for finding out
the appropriate errno.
We may want to propagate O_APPEND, or (try to) keep the current file position,
even if we use fd_reopen() to re-initialize (and "unshare") other file
description status.
For now, used only with --pty to keep/propagate O_APPEND (and/or) position
if set on stdin/stdout.
If we re-open stdout and "drop" the O_APPEND,
we get rather "unexpected" behavior,
for example with repeated "systemd-run --pty >> some-log".
If someone carefully pre-positioned the passed in original file descriptors,
we avoid surprises if we do not reset file postition to zero.
fcntl F_GETFL first, and propagate O_APPEND if present in the existing flags.
Then use lseek to propagate the file position.
Let's make fd_verify_safe_flags() even more useful:
1. let's return the cleaned up flags (i.e. just the access mode) after
validation, hiding all the noise, such as O_NOFOLLOW, O_LARGEFILE and
similar.
2. let's add a "full" version of the call that allows passing additional
flags that are OK to be set.
Adds a SAFE_FD_FLAGS define to list out all the safe FD flags, and also
an UNSAFE_FD_FLAGS() macro to strip out the safe flags and leave only
the unsafe flags. This can be used to quickly check if any unsafe flags
are set and print them for diagnostic purposes
This is useful for situations where an array of FDs is to be passed into
a child process (i.e. by passing it through safe_fork). This function
can be called in the child (before calling exec) to pack the FDs to all
be next to each-other starting from SD_LISTEN_FDS_START (i.e. 3)
Just a function to be used as a destructor (i.e. in a _cleanup_
attribute, hash table operations, etc.) that closes an fd wrapped in
FD_TO_PTR
It just retrieves the fd via PTR_TO_FD and closes it
This is just like FORMAT_PROC_FD_PATH() but goes via the PID number
rather than the "self" symlink.
This is useful whenever we want to generate a path that is useful
outside of our local scope.
We use it for more than just pipe() arrays. For example also for
socketpair(). Hence let's give it a generic name.
Also add EBADF_TRIPLET to mirror this for things like
stdin/stdout/stderr arrays, which we use a bunch of times.
Currently, we mount via file descriptors using /proc/self/fd. This
works, but it means that in /proc/mounts and various other files,
the source of the mount will be listed as /proc/self/fd/xxx. For other
software that parses these files, /proc/self/fd/xxx doesn't mean anything,
or worse, it means the completely wrong thing, as it will refer to one of
their own file descriptors instead.
Let's improve the situation by using /proc/pid/fd instead. This allows
processes parsing /proc/mounts to do the right thing more often than not.
One scenario where even this doesn't work if when containers are involved,
as with the pid namespace unshared, even /proc/pid/fd will mean the wrong
thing, but it's no worse than /proc/self/fd which will always means the wrong
thing.
This also doesn't work if we mount via file descriptor and then exit, as the pid will
be gone, but it does work as long as the process that did the mount is alive, which
makes it useful for systemd-dissect --with for example if the program we run in the
image wants to parse /proc/mounts.
In chaseat() we call dir_fd_is_root() several places, and the final
result depends on it. If the root path specified to `chase()` is not
normalized but points to "/", e.g. "/../", assertions in `chaseat()` or
`chase()` may be triggered.
Yu Watanabe
Lennart Poettering
Daan De Meyer
Mike Yuan
Lennart Poettering
Daan De Meyer
Chris Down
Zbigniew Jędrzejewski-Szmek
Lars Ellenberg
Adrian Vovk
Luca Boccassi
Dan Streetman