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From: Qian Cai <>
To: "Eric W. Biederman" <>
Cc: Alexey Gladkov <>, Yu Zhao <>,
Subject: Re: BUG: KASAN: use-after-free in dec_rlimit_ucounts
Date: Thu, 18 Nov 2021 15:32:33 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Thu, Nov 18, 2021 at 01:46:05PM -0600, Eric W. Biederman wrote:
> Is it possible?  Yes it is possible.  That is one place where
> a use-after-free has shown up and I expect would show up in the
> future.
> That said it is hard to believe there is still a user-after-free in the
> code.  We spent the last kernel development cycle pouring through and
> correcting everything we saw until we ultimately found one very subtle
> use-after-free.
> If you have a reliable reproducer that you can share, we can look into
> this and see if we can track down where the reference count is going
> bad.
> It tends to take instrumenting the entire life cycle every increment and
> every decrement and then pouring through the logs to track down a
> use-after-free.  Which is not something we can really do without a
> reproducer.

The reproducer is just to run trinity by an unprivileged user on defconfig
with KASAN enabled (On linux-next, you can do "make defconfig debug.conf"
[1], but dont think other debugging options are relevent here.)

$ trinity -C 31 -N 10000000

It is always reproduced on an arm64 server here within 5-minute so far.
Some debugging progress so far. BTW, this could happen on user_shm_unlock()
path as well.

 Call trace:
  (inlined by) user_shm_unlock at mm/mlock.c:854

I noticed in dec_rlimit_ucounts(), dec == 0 and type ==


  reply	other threads:[~2021-11-18 20:32 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-17 22:00 Qian Cai
2021-11-18 19:46 ` Eric W. Biederman
2021-11-18 20:32   ` Qian Cai [this message]
2021-11-18 20:57     ` Eric W. Biederman
2021-11-19 13:32       ` Qian Cai
2021-11-24 21:49       ` Qian Cai
2021-11-26  5:34         ` Qian Cai
2021-12-20  5:58           ` Eric W. Biederman
2021-12-21 13:09             ` Alexey Gladkov
2021-12-27 15:22               ` Eric W. Biederman

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