linux-kernel - Re: [bug] crash when reading /proc/mounts (was: Re: Linux 2.6.23-rc9 and a heads-up for the 2.6.24 series..)

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Message-ID: <20071003140842.GA8837@elte.hu>
Date:	Wed, 3 Oct 2007 16:08:42 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Al Viro <viro@....linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [bug] crash when reading /proc/mounts (was: Re: Linux
	2.6.23-rc9 and a heads-up for the 2.6.24 series..)

* Al Viro <viro@....linux.org.uk> wrote:

> On Wed, Oct 03, 2007 at 10:46:07AM +0200, Ingo Molnar wrote:
> > 
> > hm, i just triggered the procfs crash below with -rc9 on a testbox. 
> > Config attached. It's easy to reproduce it via 'service sshd restart'. 
> > The crash site is:
> > 
> >  (gdb) list *0xc017599d
> >  0xc017599d is in seq_path (fs/seq_file.c:354).
> >  349             if (m->count < m->size) {
> >  350                     char *s = m->buf + m->count;
> >  351                     char *p = d_path(dentry, mnt, s, m->size - m->count);
> >  352                     if (!IS_ERR(p)) {
> >  353                             while (s <= p) {
> >  354                                     char c = *p++;
> >  355                                     if (!c) {
> >  356                                             p = m->buf + m->count;
> >  357                                             m->count = s - m->buf;
> >  358                                             return s - p;
> >  (gdb)
> > 
> > any ideas? Fortunately i was able to do an strace of the incident:
> 
> Charming...  So we get d_path() either returning junk or we get 
> something that isn't NUL-terminated.  Which one it is?  I.e. what does 
> p look like and what's in s?

could be use-after-free as well, as CONFIG_PAGEALLOC was enabled.

	Ingo
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