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

NeilBrown
2011-07-20T00:47:38Z

On Wed, 20 Jul 2011 00:55:15 +0100 Al Viro <viro@ZenIV.linux.org.uk> wrote:

> 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.

Thanks.. but that patch seems to introduce an unused variable "seq".

NeilBrown

>
> 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(-)