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process-util: handle pidfd_spawn() returning E2BIG

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In some kernels (specifically, 5.4) even though the clone3 syscall is
supported, setting CLONE_INTO_CGROUP is not. The error message returned
in this case is E2BIG.

If posix_spawn_wrapper encounters this error, it does not retry, and
cannot spawn any programs in said kernels.

This commit adds a check for the E2BIG error and retries pidfd_spawn()
without the POSIX_SPAWN_SETCGROUP flag.

If we encounter an E2BIG error, and the pidfd_spawn() succeeds after
removing the POSIX_SPAWN_SETCGROUP flag, then we cache the result so
that we do not retry every time.

Originally, this issue was reported in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1077204.

Signed-off-by: Kornilios Kourtis <kornilios@gmail.com>
This commit is contained in:
Kornilios Kourtis 2024-08-15 17:22:35 +02:00 committed by Yu Watanabe
parent c8e7cfeddc
commit 7ac58157ca
1 changed files with 21 additions and 5 deletions
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26
src/basic/process-util.c
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@ -2059,9 +2059,10 @@ int posix_spawn_wrapper(
_unused_ _cleanup_(posix_spawnattr_destroyp) posix_spawnattr_t *attr_destructor = &attr;
#if HAVE_PIDFD_SPAWN
static bool setcgroup_supported = true;
_cleanup_close_ int cgroup_fd = -EBADF;
if (cgroup) {
if (cgroup && setcgroup_supported) {
_cleanup_free_ char *resolved_cgroup = NULL;
r = cg_get_path_and_check(
@ -2095,6 +2096,19 @@ int posix_spawn_wrapper(
_cleanup_close_ int pidfd = -EBADF;
r = pidfd_spawn(&pidfd, path, NULL, &attr, argv, envp);
if (r == E2BIG && FLAGS_SET(flags, POSIX_SPAWN_SETCGROUP)) {
/* Some kernels (e.g., 5.4) support clone3 but they do not support CLONE_INTO_CGROUP.
* Retry pidfd_spawn() after removing the flag. */
flags &= ~POSIX_SPAWN_SETCGROUP;
r = posix_spawnattr_setflags(&attr, flags);
if (r != 0)
return -r;
r = pidfd_spawn(&pidfd, path, NULL, &attr, argv, envp);
/* if pidfd_spawn was successful after removing SPAWN_CGROUP,
* mark setcgroup_supported as false so that we do not retry every time */
if (r == 0)
setcgroup_supported = false;
}
if (r == 0) {
r = pidref_set_pidfd_consume(ret_pidref, TAKE_FD(pidfd));
if (r < 0)
@ -2113,10 +2127,12 @@ int posix_spawn_wrapper(
/* Compiled on a newer host, or seccomp&friends blocking clone3()? Fallback, but need to change the
* flags to remove the cgroup one, which is what redirects to clone3() */
flags &= ~POSIX_SPAWN_SETCGROUP;
r = posix_spawnattr_setflags(&attr, flags);
if (r != 0)
return -r;
if (FLAGS_SET(flags, POSIX_SPAWN_SETCGROUP)) {
flags &= ~POSIX_SPAWN_SETCGROUP;
r = posix_spawnattr_setflags(&attr, flags);
if (r != 0)
return -r;
}
#endif
pid_t pid;