linux-kernel - Re: [PATCH] ipc,msg: shorten critical region in msgsnd

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Date:	Thu, 12 Sep 2013 17:10:01 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	davidlohr.bueso@...com
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sedat Dilek <sedat.dilek@...il.com>
Subject: Re: [PATCH] ipc,msg: shorten critical region in msgsnd

Hi all,

On 09/12/2013 02:20 PM, Manfred Spraul wrote:
>
> And: What about the other users of obtain_object_check?
> exit_sem() is also quite long, but I didn't spot any obvious problems.
>
a) I think semtimed(), msgsnd() and msgrcv() must be fixed:
They either leak memory or tasks can sleep forever.
I haven't checked the shm code, I would expect that there are similar 
problems.

b) There are additional races at least with selinux:
security/selinux/hooks.c
- selinux_sem_semop() accesses sma->sem_perm.security->sid.
- selinux_sem_free_security() does kfree() q_perm.security.

Right now, both operations can happen in parallel -> use after free.

I think the security_xx_yy() calls within ipc/*.c must only be called:
     - after checking _perm.deleted
     - with ipc_perm.lock acquired (to prevent parallel RMID calls).

Davidlohr:
What would be your proposal?

--
     Manfred
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