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core: limit number of LogExtraFields

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We have two places where those fields can be set: config and the dbus
interface. Let's clamp down on the number in both places. But in principle, we
could also be upgrading (through serialization/deserialization) from an older
systemd which didn't enforce this limit, so also check on deserialization. A
user could have a unit with lots and lots of ExtraFields, but not enough to
cause the issue in #40916. To handle this gracefully, ignore the extra fields,
like we do in the parser. Where the field is used, assert that we are within
the expected bounds.

Fixes #40916.

Reproducer:
$ python3 -c 'from pydbus import SystemBus; from gi.repository import GLib; SystemBus().get("org.freedesktop.systemd1", "/org/freedesktop/systemd1").StartTransientUnit("crash.service", "fail", [("ExecStart", GLib.Variant("a(sasb)", [("/bin/true", ["/bin/true"], False)])), ("LogExtraFields", GLib.Variant("aay", [b"F%d=x" % i for i in range(140000)]))], [])'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
    from pydbus import SystemBus; from gi.repository import GLib; SystemBus().get("org.freedesktop.systemd1", "/org/freedesktop/systemd1").StartTransientUnit("crash.service", "fail", [("ExecStart", GLib.Variant("a(sasb)", [("/bin/true", ["/bin/true"], False)])), ("LogExtraFields", GLib.Variant("aay", [b"F%d=x" % i for i in range(140000)]))], [])
                                                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.14/site-packages/pydbus/proxy_method.py", line 102, in __call__
    raise error
  File "/usr/lib/python3.14/site-packages/pydbus/proxy_method.py", line 97, in __call__
    result = instance._bus.con.call_sync(*call_args)
gi.repository.GLib.GError: g-dbus-error-quark: GDBus.Error:org.freedesktop.DBus.Error.InvalidArgs: Too many extra log fields. (16)
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
2026-03-11 18:09:27 +01:00
parent 44b050fe76
commit 456a277d3f
5 changed files with 22 additions and 0 deletions
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src/core/execute-serialize.c
+6
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@@ -30,6 +30,7 @@
#include "string-util.h"
#include "strv.h"
#include "time-util.h"
#include "unit.h"
static int exec_cgroup_context_serialize(const CGroupContext *c, FILE *f) {
_cleanup_free_ char *disable_controllers_str = NULL, *delegate_controllers_str = NULL,
@@ -3104,6 +3105,11 @@ static int exec_context_deserialize(ExecContext *c, FILE *f) {
if (r < 0)
return r;
} else if ((val = startswith(l, "exec-context-log-extra-fields="))) {
if (c->n_log_extra_fields >= LOG_EXTRA_FIELDS_MAX) {
log_warning("Too many extra log fields, ignoring.");
continue;
}
if (!GREEDY_REALLOC(c->log_extra_fields, c->n_log_extra_fields + 1))
return log_oom_debug();