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

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Message-ID: <20090331061953.GT28946@ZenIV.linux.org.uk>
Date:	Tue, 31 Mar 2009 07:19:53 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Hugh Dickins <hugh@...itas.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 Mon, Mar 30, 2009 at 06:45:39PM -0500, Serge E. Hallyn wrote:

> (note exactly *meaningful* review, but)
> 
> exit_fs() and daemonize_fs_struct() do:
> 
>                 if (--fs->users)
>                         fs = NULL;
>                 write_unlock(&fs->lock);
> 
> Moving the write_unlock up actually let's the kernel boot and
> start running ltp.

Correct fix is
		kill = !--fs->users;
		write_unlock(&fs->lock);
		...
		if (kill)
			free_fs_struct(fs);
and similar in other places with the same idiocy (one of which forgets to
unlock, on top of everything else).

Anyway, hopefully much saner (== looked through after getting some sleep,
as opposed to "what I've got in that branch at ~26 hours of uptime")
variant is in the same repository, same branch.
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