Re: [PATCH] nfs: check a crash in nfs_lookup_revalidate

[Tyler Hicks <tyhicks@linux.vnet.ibm.com>]

On Wed May 11, 2011 at 05:08:45PM -0400, 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.

But you _did_ support it up until
34286d66 "fs: rcu-walk aware d_revalidate method"

I see why you wouldn't want NULL nameidata in the NFSv4 specific
functions, but don't quite understand the opposition against it in NFSv3
(nfs_lookup_revalidate). The one-liner above would allow users to begin
using eCryptfs on top of NFSv3 clients immediately, with no side effects
to NFS.

Tyler

> 
> IOW: Feel free to change the above to.
> 
> if (nd == NULL)
>      return -EIO;
> 
> 
> 
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer
> 
> NetApp
> Trond.Myklebust@netapp.com
> www.netapp.com
> 
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