diff options
| author | Eric W. Biederman <ebiederm@xmission.com> | 2020-12-03 14:12:00 -0600 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-01-09 13:44:55 +0100 |
| commit | 117433236ae296d9770442960ddf57459177e90e (patch) | |
| tree | df326ab449c44e7768532de5aa3bc89b4fd68a93 /include/linux/sched | |
| parent | d390fc97df62dd76770eeab53f78e8ce2a07113d (diff) | |
exec: Transform exec_update_mutex into a rw_semaphore
[ Upstream commit f7cfd871ae0c5008d94b6f66834e7845caa93c15 ]
Recently syzbot reported[0] that there is a deadlock amongst the users
of exec_update_mutex. The problematic lock ordering found by lockdep
was:
perf_event_open (exec_update_mutex -> ovl_i_mutex)
chown (ovl_i_mutex -> sb_writes)
sendfile (sb_writes -> p->lock)
by reading from a proc file and writing to overlayfs
proc_pid_syscall (p->lock -> exec_update_mutex)
While looking at possible solutions it occured to me that all of the
users and possible users involved only wanted to state of the given
process to remain the same. They are all readers. The only writer is
exec.
There is no reason for readers to block on each other. So fix
this deadlock by transforming exec_update_mutex into a rw_semaphore
named exec_update_lock that only exec takes for writing.
Cc: Jann Horn <jannh@google.com>
Cc: Vasiliy Kulikov <segoon@openwall.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Christopher Yeoh <cyeoh@au1.ibm.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Fixes: eea9673250db ("exec: Add exec_update_mutex to replace cred_guard_mutex")
[0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com
Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com
Link: https://lkml.kernel.org/r/87ft4mbqen.fsf@x220.int.ebiederm.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'include/linux/sched')
| -rw-r--r-- | include/linux/sched/signal.h | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index a29df79540ce..baf58f4cb057 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -226,12 +226,13 @@ struct signal_struct { * credential calculations * (notably. ptrace) * Deprecated do not use in new code. - * Use exec_update_mutex instead. - */ - struct mutex exec_update_mutex; /* Held while task_struct is being - * updated during exec, and may have - * inconsistent permissions. + * Use exec_update_lock instead. */ + struct rw_semaphore exec_update_lock; /* Held while task_struct is + * being updated during exec, + * and may have inconsistent + * permissions. + */ } __randomize_layout; /* |