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Date: Thu, 23 Aug 2012 08:12:30 -0400
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Al Viro <viro@zeniv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Pavel Emelyanov <xemul@parallels.com>,
        James Bottomley <jbottomley@parallels.com>,
        Matthew Helsley <matt.helsley@gmail.com>,
        aneesh.kumar@linux.vnet.ibm.com
Subject: Re: [patch 4/9] fs, exportfs: Fix nil dereference if no
 s_export_op present
Message-ID: <20120823121230.GC29943@fieldses.org>
References: <20120823104323.040550004@openvz.org>
 <20120823104725.830795272@openvz.org>
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On Thu, Aug 23, 2012 at 02:43:27PM +0400, Cyrill Gorcunov wrote:
> If there is no s_export_op present in a target superblock
> we might have nil dereference.

Is that NULL dereference possible with current code, or is it a check
you're adding to account for a new caller that you're about to add?

I believe it's the latter, but this would be a good thing to make clear
in the changelog.

--b.

> Fix it with eplicit test
> if s_export_op is provided.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
> CC: Pavel Emelyanov <xemul@parallels.com>
> CC: Al Viro <viro@ZenIV.linux.org.uk>
> CC: Alexey Dobriyan <adobriyan@gmail.com>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: James Bottomley <jbottomley@parallels.com>
> CC: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> CC: Alexey Dobriyan <adobriyan@gmail.com>
> CC: Matthew Helsley <matt.helsley@gmail.com>
> CC: "J. Bruce Fields" <bfields@fieldses.org>
> CC: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> ---
>  fs/exportfs/expfs.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6.git/fs/exportfs/expfs.c
> ===================================================================
> --- linux-2.6.git.orig/fs/exportfs/expfs.c
> +++ linux-2.6.git/fs/exportfs/expfs.c
> @@ -357,7 +357,7 @@ int exportfs_encode_fh(struct dentry *de
>  		 */
>  		parent = p->d_inode;
>  	}
> -	if (nop->encode_fh)
> +	if (nop && nop->encode_fh)
>  		error = nop->encode_fh(inode, fid->raw, max_len, parent);
>  	else
>  		error = export_encode_fh(inode, fid, max_len, parent);
>