[PATCH AUTOSEL 5.4 202/330] proc: Use new infrastructure to fix deadlocks in execve

[Sasha Levin]

From: Bernd Edlinger <bernd.edlinger@xxxxxxxxxx>

[ Upstream commit 2db9dbf71bf98d02a0bf33e798e5bfd2a9944696 ]

This changes lock_trace to use the new exec_update_mutex
instead of cred_guard_mutex.

This fixes possible deadlocks when the trace is accessing
/proc/$pid/stack for instance.

This should be safe, as the credentials are only used for reading,
and task->mm is updated on execve under the new exec_update_mutex.

Signed-off-by: Bernd Edlinger <bernd.edlinger@xxxxxxxxxx>
Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/proc/base.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ebea9501afb84..4fdfe4faa74ee 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -403,11 +403,11 @@ print0:
 
 static int lock_trace(struct task_struct *task)
 {
-	int err = mutex_lock_killable(&task->signal->cred_guard_mutex);
+	int err = mutex_lock_killable(&task->signal->exec_update_mutex);
 	if (err)
 		return err;
 	if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_FSCREDS)) {
-		mutex_unlock(&task->signal->cred_guard_mutex);
+		mutex_unlock(&task->signal->exec_update_mutex);
 		return -EPERM;
 	}
 	return 0;
@@ -415,7 +415,7 @@ static int lock_trace(struct task_struct *task)
 
 static void unlock_trace(struct task_struct *task)
 {
-	mutex_unlock(&task->signal->cred_guard_mutex);
+	mutex_unlock(&task->signal->exec_update_mutex);
 }
 
 #ifdef CONFIG_STACKTRACE
-- 
2.25.1