linux-kernel - [PATCH 5.4 197/388] proc: io_accounting: Use new infrastructure to fix deadlocks in execve

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Date:   Tue, 29 Sep 2020 12:58:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bernd Edlinger <bernd.edlinger@...mail.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 197/388] proc: io_accounting: Use new infrastructure to fix deadlocks in execve

From: Bernd Edlinger <bernd.edlinger@...mail.de>

[ Upstream commit 76518d3798855242817e8a8ed76b2d72f4415624 ]

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

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

This should be safe, as the credentials are only used for reading.

Signed-off-by: Bernd Edlinger <bernd.edlinger@...mail.de>
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/proc/base.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4fdfe4faa74ee..529d0c6ec6f9c 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2770,7 +2770,7 @@ 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->cred_guard_mutex);
+	result = mutex_lock_killable(&task->signal->exec_update_mutex);
 	if (result)
 		return result;
 
@@ -2806,7 +2806,7 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh
 	result = 0;
 
 out_unlock:
-	mutex_unlock(&task->signal->cred_guard_mutex);
+	mutex_unlock(&task->signal->exec_update_mutex);
 	return result;
 }
 
-- 
2.25.1