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From: Andrew Morton <akpm@linux-foundation.org>
To: Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
Cc: linux-kernel@vger.kernel.org, Milton Miller <miltonm@bga.com>,
	Jack Miller <millerjo@us.ibm.com>,
	Pavel Tikhomirov <ptikhomirov@virtuozzo.com>,
	Alexander Mikhalitsyn <alexander@mihalicyn.com>,
	Manfred Spraul <manfred@colorfullife.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@suse.com>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH 0/2] shm: omit forced shm destroy if task IPC namespace was changed
Date: Fri, 9 Jul 2021 18:12:41 -0700	[thread overview]
Message-ID: <20210709181241.cca57cf83c52964b2cd0dcf0@linux-foundation.org> (raw)
In-Reply-To: <20210706132259.71740-1-alexander.mikhalitsyn@virtuozzo.com>

On Tue,  6 Jul 2021 16:22:57 +0300 Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com> wrote:

> Hello,
> 
> Task IPC namespace shm's has shm_rmid_forced feature which is per IPC namespace
> and controlled by kernel.shm_rmid_forced sysctl. When feature is turned on,
> then during task exit (and unshare(CLONE_NEWIPC)) all sysvshm's will be destroyed
> by exit_shm(struct task_struct *task) function. But there is a problem if task
> was changed IPC namespace since shmget() call. In such situation exit_shm() function
> will try to call
> shm_destroy(<new_ipc_namespace_ptr>, <sysvshmem_from_old_ipc_namespace>)
> which leads to the situation when sysvshm object still attached to old
> IPC namespace but freed; later during old IPC namespace cleanup we will try to
> free such sysvshm object for the second time and will get the problem :)
> 
> First patch solves this problem by postponing shm_destroy to the moment when
> IPC namespace cleanup will be called.
> Second patch is useful to prevent (or easy catch) such bugs in the future by
> adding corresponding WARNings.
> 

(cc's added)

I assume that a

Fixes: b34a6b1da371ed8af ("ipc: introduce shm_rmid_forced sysctl") is
appropriate here?

A double-free is serious.  Should this fix be backported into earlier
kernels?

  parent reply	other threads:[~2021-07-10  1:12 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-06 13:22 Alexander Mikhalitsyn
2021-07-06 13:22 ` [PATCH 1/2] shm: skip shm_destroy " Alexander Mikhalitsyn
2021-07-06 13:22 ` [PATCH 2/2] ipc: WARN if trying to remove ipc object which is absent Alexander Mikhalitsyn
2021-07-10  1:12 ` Andrew Morton [this message]
2021-07-10 10:55   ` [PATCH 0/2] shm: omit forced shm destroy if task IPC namespace was changed Alexander Mihalicyn
     [not found]     ` <CALgW_8VUk0us_umLncUv2DUMkOi3qixmT+YkHV4Dhpt_nNMZHw@mail.gmail.com>
2021-07-11 10:33       ` Alexander Mihalicyn
2021-07-11 11:46         ` Manfred Spraul
2021-07-12  9:54           ` Alexander Mihalicyn
2021-07-12 19:18             ` Eric W. Biederman
2021-07-12 19:27               ` Alexander Mihalicyn
2021-07-14 17:30                 ` [RFC PATCH] shm: extend forced shm destroy to support objects from several IPC nses Alexander Mikhalitsyn
2021-07-21  6:32                   ` Manfred Spraul
2021-07-22 18:46                   ` Manfred Spraul
2021-07-30 14:52                     ` Alexander Mihalicyn
2021-07-14 17:42                 ` [PATCH 0/2] shm: omit forced shm destroy if task IPC namespace was changed Alexander Mihalicyn
2021-09-23 16:36               ` Manfred Spraul
2021-09-24 16:45                 ` Eric W. Biederman

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