linux-kernel - Re: [PATCH] vfs: fix race in rcu lookup of pruned dentry

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 18 Jul 2011 19:20:30 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...nel.dk>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] vfs: fix race in rcu lookup of pruned dentry

On Mon, Jul 18, 2011 at 11:11:40AM -0700, Linus Torvalds wrote:

> Also, looking at that whole mount-point traversal sequence, it looks
> like __follow_mount_rcu() will happily totally ignore the old sequence
> number when it replaces it with the mount-point sequence number. So it
> looks to me that we have a case where we miss the sequence number
> check that can happen with a positive dentry too!
> 
> No?
> 
> So I think that whenever we change "nd->seq", we should always heck
> the previous sequence number first (the way do_lookup() itself does
> for the *normal* traversal case). Otherwise we will have traversed the
> mount-point without ever having checked the previous sequence number.
> 
> Something like the (untested) attached patch.
> 
> Comments? This mount-point case is independent of the negative dentry
> issue, and probably never really an issue in practice, but...

->mnt_mountpoint and ->mnt_root are both pinned (and protected by
vfsmount_lock, while we are at it).  If it manages to get stale,
we have worse problems...
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/