diff options
| author | Oleg Nesterov <oleg@redhat.com> | 2025-03-24 17:00:03 +0100 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2025-03-25 14:59:05 +0100 |
| commit | af7bb0d2ca459f15cb5ca604dab5d9af103643f0 (patch) | |
| tree | 4681876f8bf4c256905b50d781315b718922bddd /fs/exec.c | |
| parent | 8661bb9c717a07b7636224339fe8818b65db6ddf (diff) | |
exec: fix the racy usage of fs_struct->in_exec
check_unsafe_exec() sets fs->in_exec under cred_guard_mutex, then execve()
paths clear fs->in_exec lockless. This is fine if exec succeeds, but if it
fails we have the following race:
T1 sets fs->in_exec = 1, fails, drops cred_guard_mutex
T2 sets fs->in_exec = 1
T1 clears fs->in_exec
T2 continues with fs->in_exec == 0
Change fs/exec.c to clear fs->in_exec with cred_guard_mutex held.
Reported-by: syzbot+1c486d0b62032c82a968@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/67dc67f0.050a0220.25ae54.001f.GAE@google.com/
Cc: stable@vger.kernel.org
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250324160003.GA8878@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'fs/exec.c')
| -rw-r--r-- | fs/exec.c | 15 |
1 files changed, 9 insertions, 6 deletions
diff --git a/fs/exec.c b/fs/exec.c index f45859ad13ac..5d1c0d2dc403 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1227,13 +1227,12 @@ int begin_new_exec(struct linux_binprm * bprm) */ bprm->point_of_no_return = true; - /* - * Make this the only thread in the thread group. - */ + /* Make this the only thread in the thread group */ retval = de_thread(me); if (retval) goto out; - + /* see the comment in check_unsafe_exec() */ + current->fs->in_exec = 0; /* * Cancel any io_uring activity across execve */ @@ -1495,6 +1494,8 @@ static void free_bprm(struct linux_binprm *bprm) } free_arg_pages(bprm); if (bprm->cred) { + /* in case exec fails before de_thread() succeeds */ + current->fs->in_exec = 0; mutex_unlock(¤t->signal->cred_guard_mutex); abort_creds(bprm->cred); } @@ -1616,6 +1617,10 @@ static void check_unsafe_exec(struct linux_binprm *bprm) * suid exec because the differently privileged task * will be able to manipulate the current directory, etc. * It would be nice to force an unshare instead... + * + * Otherwise we set fs->in_exec = 1 to deny clone(CLONE_FS) + * from another sub-thread until de_thread() succeeds, this + * state is protected by cred_guard_mutex we hold. */ n_fs = 1; spin_lock(&p->fs->lock); @@ -1860,7 +1865,6 @@ static int bprm_execve(struct linux_binprm *bprm) sched_mm_cid_after_execve(current); /* execve succeeded */ - current->fs->in_exec = 0; current->in_execve = 0; rseq_execve(current); user_events_execve(current); @@ -1879,7 +1883,6 @@ out: force_fatal_sig(SIGSEGV); sched_mm_cid_after_execve(current); - current->fs->in_exec = 0; current->in_execve = 0; return retval; |