From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Subject: Re: [PATCH] cifs: cope with negative dentries in cifs_get_root
Date: Tue, 9 Aug 2011 07:38:00 +0100
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Cc: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, smfrench-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
	linux-cifs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
To: Pavel Shilovsky <piastryyy-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
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On Tue, Aug 09, 2011 at 09:41:33AM +0400, Pavel Shilovsky wrote:
> > ? ? ? ? ? ? ? ?mutex_unlock(&dir->i_mutex);
> > ? ? ? ? ? ? ? ?dput(dentry);
> > ? ? ? ? ? ? ? ?dentry = child;
> > + ? ? ? ? ? ? ? if (!dentry->d_inode) {
> 
> dentry can be NULL here (returned from lookup_one_len) and it can
> cause a null pointer dereference.

Not NULL, ERR_PTR(...).  IOW, we need to check IS_ERR(dentry) to protect
that check of dentry->d_inode.