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

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Message-ID: <20090330234539.GA3462@us.ibm.com>
Date:	Mon, 30 Mar 2009 18:45:39 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Al Viro <viro@...IV.linux.org.uk>
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)

Quoting Al Viro (viro@...IV.linux.org.uk):
> On Mon, Mar 30, 2009 at 03:40:40AM +0200, Oleg Nesterov wrote:
> 
> > > We can't proceed. If that another exec() fails, it will clear "under exec" at
> > > the end of do_execve(), before we kill other threads.
> > 
> > Or we need a counter to mark/unmark.
> 
> Nah, easier to have check_unsafe_exec() return -EAGAIN in cases we care
> about.
> 
> Anyway, completely untested patchset is in
> git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6.git/ execve-mess
> (the last 9 changesets of it).
> 
> WARNING: that's *NOT* for merge at the moment; this is not a pull request.
> 
> Review (and testing) would be welcome.

(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.

-serge
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