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Subject: Re: [PATCH] nfs: check a crash in nfs_lookup_revalidate
From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: Peng Huang <shawn.p.huang@gmail.com>
Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org
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Date: Wed, 11 May 2011 18:08:43 -0400
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On Wed, 2011-05-11 at 17:35 -0400, Peng Huang wrote:
> On Wed, May 11, 2011 at 5:08 PM, Trond Myklebust
> <Trond.Myklebust@netapp.com> wrote:
> > On Wed, 2011-05-11 at 17:03 -0400, Peng Huang wrote:
> >> lookup_one_len() may call nfs_loopup_revalidate() with nd == NULL
> >> indirectly, that causes the kernel crash.
> >>
> >> RIP: 0010:[<ffffffffa0ba3b41>]  [<ffffffffa0ba3b41>]
> >> nfs_lookup_revalidate+0x21/0x4a0 [nfs]
> >> RSP: 0018:ffff88018f00fae8  EFLAGS: 00010286
> >>
> >> Call Trace:
> >>  [<ffffffff81164a17>] do_revalidate+0x17/0x60
> >>  [<ffffffff81164e9b>] __lookup_hash+0xcb/0x140
> >>  [<ffffffff811653c4>] lookup_one_len+0x94/0xe0
> >>  [<ffffffff81241ef1>] ecryptfs_lookup+0x91/0x1d0
> >>  [<ffffffff81164d85>] d_alloc_and_lookup+0x45/0x90
> >>  [<ffffffff8116f7b5>] ? d_lookup+0x35/0x60
> >>  [<ffffffff811669b2>] do_lookup+0x192/0x2d0
> >>  [<ffffffff811763be>] ? vfsmount_lock_local_unlock+0x1e/0x30
> >>  [<ffffffff8126d09c>] ? security_inode_permission+0x1c/0x30
> >>  [<ffffffff81167d67>] link_path_walk+0x597/0xae0
> >>  [<ffffffff8117638e>] ? vfsmount_lock_local_lock+0x1e/0x30
> >>  [<ffffffff81165905>] ? path_init_rcu+0xa5/0x210
> >>  [<ffffffff8116858b>] do_path_lookup+0x5b/0x140
> >>  [<ffffffff811692f7>] user_path_at+0x57/0xa0
> >>  [<ffffffff8159fd08>] ? do_page_fault+0x1e8/0x4e0
> >>  [<ffffffff8115eb86>] vfs_fstatat+0x46/0x80
> >>  [<ffffffff8116b990>] ? filldir+0x0/0xe0
> >>  [<ffffffff8115ec2e>] vfs_lstat+0x1e/0x20
> >>  [<ffffffff8115ec54>] sys_newlstat+0x24/0x50
> >>  [<ffffffff8159c995>] ? page_fault+0x25/0x30
> >>  [<ffffffff8100bfc2>] system_call_fastpath+0x16/0x1b
> >>
> >> Signed-off-by: Peng Huang <shawn.p.huang@gmail.com>
> >> ---
> >>  fs/nfs/dir.c |    2 +-
> >>  1 files changed, 1 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> >> index 2c3eb33..9452aa5 100644
> >> --- a/fs/nfs/dir.c
> >> +++ b/fs/nfs/dir.c
> >> @@ -1028,7 +1028,7 @@ static int nfs_lookup_revalidate(struct dentry *dentry, struct nameidata *nd)
> >>       struct nfs_fattr *fattr = NULL;
> >>       int error;
> >>
> >> -     if (nd->flags & LOOKUP_RCU)
> >> +     if (nd != NULL && nd->flags & LOOKUP_RCU)
> >>               return -ECHILD;
> >>
> >>       parent = dget_parent(dentry);
> >
> > That's exactly what Tyler Hicks proposed last week and which was NACKed.
> > We simply won't support layered filesystems that don't do intents.
> >
> > IOW: Feel free to change the above to.
> >
> > if (nd == NULL)
> >     return -EIO;
> >
> 
> I tested returning -EIO when nd is NULL. Kernel does not crash, but
> ecryptfs can not work on nfs anymore.

It isn't going to work until ecryptfs gets fixed. Only blind luck made
it 'work' previously.

The above will at least ensure that if someone tries to use it over NFS,
then we won't Oops, and they will get a valid error message.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com