linux-kernel - [ 46/82] NFS: fix bug in legacy DNS resolver.

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Message-Id: <20121114053940.232994658@decadent.org.uk>
Date:	Wed, 14 Nov 2012 05:40:19 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	NeilBrown <neilb@...e.de>, Chuck Lever <chuck.lever@...cle.com>,
	Trond Myklebust <Trond.Myklebust@...app.com>
Subject: [ 46/82] NFS: fix bug in legacy DNS resolver.

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

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

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

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@...cle.com>
Tested-by: Chuck Lever <chuck.lever@...cle.com>
Signed-off-by: NeilBrown <neilb@...e.de>
Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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 31c26c4..ca4b11e 100644
--- a/fs/nfs/dns_resolve.c
+++ b/fs/nfs/dns_resolve.c
@@ -217,7 +217,7 @@ static int nfs_dns_parse(struct cache_detail *cd, char *buf, int buflen)
 {
 	char buf1[NFS_DNS_HOSTNAME_MAXLEN+1];
 	struct nfs_dns_ent key, *item;
-	unsigned long ttl;
+	unsigned int ttl;
 	ssize_t len;
 	int ret = -EINVAL;
 
@@ -240,7 +240,8 @@ 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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