linux-kernel - [PATCH] fix sighand use after free

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Date:	Wed, 13 Aug 2014 11:50:00 -0400
From:	Rik van Riel <riel@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, peterz@...radead.org, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com
Subject: [PATCH] fix sighand use after free

Subject: fix sighand use after free

__lock_task_sighand carefully takes the rcu_read_lock, gets
tsk->sighand with rcu_dereference, and verifies that the task
is still using the sighand_struct after taking the spinlock.

This works much better if the sighand struct is actually rcu
freed.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 kernel/fork.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 1380d8a..754a7c6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1017,7 +1017,7 @@ void __cleanup_sighand(struct sighand_struct *sighand)
 {
 	if (atomic_dec_and_test(&sighand->count)) {
 		signalfd_cleanup(sighand);
-		kmem_cache_free(sighand_cachep, sighand);
+		rcu_free(sighand_cachep, sighand);
 	}
 }
 

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