linux-kernel - [PATCH] exit: move exit_task_namespaces() after exit_task

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Date:   Thu, 14 Dec 2017 12:17:57 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        stable@...r.kernel.org
Subject: [PATCH] exit: move exit_task_namespaces() after exit_task_work()

syzbot reported we have a use-after-free when mqueue_evict_inode()
is called on __cleanup_mnt() path, where the ipc ns is already
freed by the previous exit_task_namespaces(). We can just move
it after after exit_task_work() to avoid this use-after-free.

Reported-by: syzbot <syzkaller@...glegroups.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: stable@...r.kernel.org
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 kernel/exit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 6b4298a41167..909e43c45158 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -861,8 +861,8 @@ void __noreturn do_exit(long code)
 	exit_fs(tsk);
 	if (group_dead)
 		disassociate_ctty(1);
-	exit_task_namespaces(tsk);
 	exit_task_work(tsk);
+	exit_task_namespaces(tsk);
 	exit_thread(tsk);
 
 	/*
-- 
2.13.0