From: Bernd Edlinger <bernd.edlinger@hotmail.de>
Date: Sat, 21 Mar 2020 02:46:16 +0000 (+0000)
Subject: pidfd: Use new infrastructure to fix deadlocks in execve
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=501f9328bf5c6b5e4863da4b50e0e86792de3aa9;p=linux.git

pidfd: Use new infrastructure to fix deadlocks in execve

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

This should be safe, as the credentials do not change
before exec_update_mutex is locked.  Therefore whatever
file access is possible with holding the cred_guard_mutex
here is also possbile with the exec_update_mutex.

Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---

diff --git a/kernel/pid.c b/kernel/pid.c
index 60820e72634c8..efd34874b3d12 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -577,7 +577,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd)
 	struct file *file;
 	int ret;
 
-	ret = mutex_lock_killable(&task->signal->cred_guard_mutex);
+	ret = mutex_lock_killable(&task->signal->exec_update_mutex);
 	if (ret)
 		return ERR_PTR(ret);
 
@@ -586,7 +586,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd)
 	else
 		file = ERR_PTR(-EPERM);
 
-	mutex_unlock(&task->signal->cred_guard_mutex);
+	mutex_unlock(&task->signal->exec_update_mutex);
 
 	return file ?: ERR_PTR(-EBADF);
 }