linux-kernel - [ 20/47] NFS: avoid NULL dereference in nfs_destroy

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Date:	Wed,  9 Jan 2013 12:35:15 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, NeilBrown <neilb@...e.de>,
	Trond Myklebust <Trond.Myklebust@...app.com>
Subject: [ 20/47] NFS: avoid NULL dereference in nfs_destroy_server

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: NeilBrown <neilb@...e.de>

commit f259613a1e4b44a0cf85a5dafd931be96ee7c9e5 upstream.

In rare circumstances, nfs_clone_server() of a v2 or v3 server can get
an error between setting server->destory (to nfs_destroy_server), and
calling nfs_start_lockd (which will set server->nlm_host).

If this happens, nfs_clone_server will call nfs_free_server which
will call nfs_destroy_server and thence nlmclnt_done(NULL).  This
causes the NULL to be dereferenced.

So add a guard to only call nlmclnt_done() if ->nlm_host is not NULL.

The other guards there are irrelevant as nlm_host can only be non-NULL
if one of these flags are set - so remove those tests.  (Thanks to Trond
for this suggestion).

This is suitable for any stable kernel since 2.6.25.

Signed-off-by: NeilBrown <neilb@...e.de>
Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/nfs/client.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -673,8 +673,7 @@ static int nfs_create_rpc_client(struct
  */
 static void nfs_destroy_server(struct nfs_server *server)
 {
-	if (!(server->flags & NFS_MOUNT_LOCAL_FLOCK) ||
-			!(server->flags & NFS_MOUNT_LOCAL_FCNTL))
+	if (server->nlm_host)
 		nlmclnt_done(server->nlm_host);
 }

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