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authorEric W. Biederman <ebiederm@xmission.com>2020-12-03 14:12:00 -0600
committerEric W. Biederman <ebiederm@xmission.com>2020-12-10 13:13:32 -0600
commitf7cfd871ae0c5008d94b6f66834e7845caa93c15 (patch)
treea08cce9a47f88e61c97aca01eff40d73920e3d21 /fs/proc
parent31784cff7ee073b34d6eddabb95e3be2880a425c (diff)
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exec: Transform exec_update_mutex into a rw_semaphore
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>
Diffstat (limited to 'fs/proc')
-rw-r--r--fs/proc/base.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c
index b362523a9829..55ce0ee9c5c7 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -405,11 +405,11 @@ print0:
static int lock_trace(struct task_struct *task)
{
- int err = mutex_lock_killable(&task->signal->exec_update_mutex);
+ int err = down_read_killable(&task->signal->exec_update_lock);
if (err)
return err;
if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_FSCREDS)) {
- mutex_unlock(&task->signal->exec_update_mutex);
+ up_read(&task->signal->exec_update_lock);
return -EPERM;
}
return 0;
@@ -417,7 +417,7 @@ static int lock_trace(struct task_struct *task)
static void unlock_trace(struct task_struct *task)
{
- mutex_unlock(&task->signal->exec_update_mutex);
+ up_read(&task->signal->exec_update_lock);
}
#ifdef CONFIG_STACKTRACE
@@ -2930,7 +2930,7 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh
unsigned long flags;
int result;
- result = mutex_lock_killable(&task->signal->exec_update_mutex);
+ result = down_read_killable(&task->signal->exec_update_lock);
if (result)
return result;
@@ -2966,7 +2966,7 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh
result = 0;
out_unlock:
- mutex_unlock(&task->signal->exec_update_mutex);
+ up_read(&task->signal->exec_update_lock);
return result;
}