linux-kernel - Re: Q: check_unsafe_exec() races (Was: [PATCH 2/4] fix setuid sometimes doesn't)

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Date:	Wed, 1 Apr 2009 04:03:39 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joe Malicki <jmalicki@...acarta.com>,
	Michael Itz <mitz@...acarta.com>,
	Kenneth Baker <bakerk@...acarta.com>,
	Chris Wright <chrisw@...s-sol.org>,
	David Howells <dhowells@...hat.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Q: check_unsafe_exec() races (Was: [PATCH 2/4] fix setuid
	sometimes doesn't)

On Wed, Apr 01, 2009 at 03:38:49AM +0100, Al Viro wrote:
> On Wed, Apr 01, 2009 at 01:28:01AM +0100, Hugh Dickins wrote:
> > Minor bisectability issue: the third patch, which introduces
> > int unshare_fs_struct(void), needs to return 0 when it succeeds:
> > that gets corrected in the fourth patch.
> 
> ACK.
> 
> > Lockdep objects to how check_unsafe_exec nests write_lock(&p->fs_lock)
> > inside lock_task_sighand(p, &flags).  It's right: we sometimes take
> > sighand->siglock in interrupt, so if such an interrupt occurred just
> > after you take fs_lock elsewhere, that could deadlock with this.  It
> > seems happy with taking fs_lock just outside the lock_task_sighand.
> 
> Right you are, check_unsafe_exec() reordered.  Will push in a few.

Rebased and pushed (same tree, same branch; included into for-next, along
with related cleanups).
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