[PATCH AUTOSEL 5.4 201/330] kernel/kcmp.c: Use new infrastructure to fix deadlocks in execve

[Sasha Levin]

From: Bernd Edlinger <bernd.edlin...@hotmail.de>

[ Upstream commit 454e3126cb842388e22df6b3ac3da44062c00765 ]

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

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

Signed-off-by: Bernd Edlinger <bernd.edlin...@hotmail.de>
Signed-off-by: Eric W. Biederman <ebied...@xmission.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 kernel/kcmp.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/kcmp.c b/kernel/kcmp.c
index a0e3d7a0e8b81..b3ff9288c6cc9 100644
--- a/kernel/kcmp.c
+++ b/kernel/kcmp.c
@@ -173,8 +173,8 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
        /*
         * One should have enough rights to inspect task details.
         */
-       ret = kcmp_lock(&task1->signal->cred_guard_mutex,
-                       &task2->signal->cred_guard_mutex);
+       ret = kcmp_lock(&task1->signal->exec_update_mutex,
+                       &task2->signal->exec_update_mutex);
        if (ret)
                goto err;
        if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
@@ -229,8 +229,8 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
        }
 
 err_unlock:
-       kcmp_unlock(&task1->signal->cred_guard_mutex,
-                   &task2->signal->cred_guard_mutex);
+       kcmp_unlock(&task1->signal->exec_update_mutex,
+                   &task2->signal->exec_update_mutex);
 err:
        put_task_struct(task1);
        put_task_struct(task2);
-- 
2.25.1