[ 3.5.y.z extended stable ] Patch "NFS: fix bug in legacy DNS resolver." has been added to staging queue

Herton Ronaldo Krzesinski herton.krzesinski at canonical.com
Wed Dec 5 22:31:40 UTC 2012

This is a note to let you know that I have just added a patch titled

    NFS: fix bug in legacy DNS resolver.

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From ab7c3e03e68f8092dd304f954ef39b125c69180b Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb at suse.de>
Date: Wed, 31 Oct 2012 12:16:01 +1100
Subject: [PATCH] NFS: fix bug in legacy DNS resolver.
X-Extended-Stable: 3.5

commit 8d96b10639fb402357b75b055b1e82a65ff95050 upstream.

The DNS resolver's use of the sunrpc cache involves a 'ttl' number
(relative) rather that a timeout (absolute).  This confused me when
I wrote
  commit c5b29f885afe890f953f7f23424045cdad31d3e4
     "sunrpc: use seconds since boot in expiry cache"

and I managed to break it.  The effect is that any TTL is interpreted
as 0, and nothing useful gets into the cache.

This patch removes the use of get_expiry() - which really expects an
expiry time - and uses get_uint() instead, treating the int correctly
as a ttl.

This fixes a regression that has been present since 2.6.37, causing
certain NFS accesses in certain environments to incorrectly fail.

Reported-by: Chuck Lever <chuck.lever at oracle.com>
Tested-by: Chuck Lever <chuck.lever at oracle.com>
Signed-off-by: NeilBrown <neilb at suse.de>
Signed-off-by: Trond Myklebust <Trond.Myklebust at netapp.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
 fs/nfs/dns_resolve.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/dns_resolve.c b/fs/nfs/dns_resolve.c
index b3924b8..786cd65 100644
--- a/fs/nfs/dns_resolve.c
+++ b/fs/nfs/dns_resolve.c
@@ -214,7 +214,7 @@ static int nfs_dns_parse(struct cache_detail *cd, char *buf, int buflen)
 	struct nfs_dns_ent key, *item;
-	unsigned long ttl;
+	unsigned int ttl;
 	ssize_t len;
 	int ret = -EINVAL;

@@ -237,7 +237,8 @@ static int nfs_dns_parse(struct cache_detail *cd, char *buf, int buflen)
 	key.namelen = len;
 	memset(&key.h, 0, sizeof(key.h));

-	ttl = get_expiry(&buf);
+	if (get_uint(&buf, &ttl) < 0)
+		goto out;
 	if (ttl == 0)
 		goto out;
 	key.h.expiry_time = ttl + seconds_since_boot();

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