linux-kernel - Re: vfs: lockdep splat with prepare_bprm

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Message-ID: <20130315042628.GV21522@ZenIV.linux.org.uk>
Date:	Fri, 15 Mar 2013 04:26:28 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Dave Jones <davej@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: vfs: lockdep splat with prepare_bprm_creds

On Fri, Mar 15, 2013 at 12:07:14AM -0400, Sasha Levin wrote:
> Hi all,
> 
> While fuzzing with trinity inside a KVM tools guest running latest -next kernel
> I've stumbled on the following.
> 
> Dave Jones reported something similar, but that seemed to involve cgroup's mutex
> and didn't seem like it was the same issue as this one.

Lovely...  It's an execve() attempt on a "binary" that is, in fact, a procfs
file (/proc/<pid>/stack), with its ->read() trying to grab ->cred_guard_mutex.
The fact that it's seq_file-based is irrelevant here - all that matters is
that we have ->read() for some file trying to grab ->cred_guard_mutex.

It's not *quite* a deadlock, though - all these guys are using
mutex_lock_killable()...
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