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

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Message-ID: <20110719235515.GT11013@ZenIV.linux.org.uk>
Date:	Wed, 20 Jul 2011 00:55:15 +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, neilb@...e.de
Subject: Re: [PATCH] vfs: fix race in rcu lookup of pruned dentry

On Wed, Jul 20, 2011 at 12:52:16AM +0100, Al Viro wrote:
> On Wed, Jul 20, 2011 at 12:45:51AM +0100, Al Viro wrote:
> 
> > You know what...  I doubt that you want to mess with ->d_seq checks here.
> > It's definitely not Hugh's bug (unless he has bindings somewhere odd) and
> > both ->mnt_mountpoint and ->mnt_root are pinned (and we are holding
> > vfsmount_lock anyway).  *inode assignment too early is a real bug, indeed,
> > and we want to assign nd->seq if we cross mountpoint as both versions do,
> > but check just before that is, in the best case, BUG_ON() fodder.  We'd
> > just found a vfsmount with ->mnt_mountpoint equal to path->dentry; it *can't*
> > be stale, or we have a really nasty problem anyway.
> 
> Kudos to neilb for spotting the pointless check, BTW; and no, his theory
> that it might be needed since we could race with umount() is wrong - due to
> vfsmount_lock being held.

Updated, pushed.  Please, pull from the usual place (
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6.git/ for-linus
).

Shortlog:
Al Viro (1):
      Fix cifs_get_root()

Linus Torvalds (1):
      vfs: fix race in rcu lookup of pruned dentry

Diffstat:
 fs/cifs/cifsfs.c |  100 +++++++++++++++--------------------------------------
 fs/namei.c       |   10 +++++-
 2 files changed, 38 insertions(+), 72 deletions(-)
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