[PATCH v6 14/16] 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 <redacted>
---
 kernel/pid.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index 0f4ecb5..04821f4 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c

@@ -584,7 +584,7 @@ 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);
 

@@ -593,7 +593,7 @@ 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);
 }

-- 
1.9.1

On Sat, Mar 21, 2020 at 02:46:16AM +0000, Bernd Edlinger wrote:

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 <redacted>

Reviewed-by: Christian Brauner <redacted>