knfsd: use a spinlock to protect sk_info_authunix

sk_info_authunix is not being protected properly so the object that it
points to can be cache_put twice, leading to corruption.

We borrow svsk->sk_defer_lock to provide the protection.  We should
probably rename that lock to have a more generic name - later.

Thanks to Gabriel for reporting this.

Cc: Greg Banks <gnb@melbourne.sgi.com>
Cc: Gabriel Barazer <gabriel@oxeva.fr>
Signed-off-by: Neil Brown <neilb@suse.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 5 deletions

diff --git a/net/sunrpc/svcauth_unix.c b/net/sunrpc/svcauth_unix.c
index 9bae4090254c..2bd23ea2aa8b 100644
--- a/net/sunrpc/svcauth_unix.c
+++ b/net/sunrpc/svcauth_unix.c
@@ -383,7 +383,10 @@ void svcauth_unix_purge(void)
 static inline struct ip_map *
 ip_map_cached_get(struct svc_rqst *rqstp)
 {
-        struct ip_map *ipm = rqstp->rq_sock->sk_info_authunix;
+        struct ip_map *ipm;
+        struct svc_sock *svsk = rqstp->rq_sock;
+        spin_lock_bh(&svsk->sk_defer_lock);
+        ipm = svsk->sk_info_authunix;
         if (ipm != NULL) {
                 if (!cache_valid(&ipm->h)) {
                         /*
@@ -391,12 +394,14 @@ ip_map_cached_get(struct svc_rqst *rqstp)
                          * remembered, e.g. by a second mount from the
                          * same IP address.
                          */
-                        rqstp->rq_sock->sk_info_authunix = NULL;
+                        svsk->sk_info_authunix = NULL;
+                        spin_unlock_bh(&svsk->sk_defer_lock);
                         cache_put(&ipm->h, &ip_map_cache);
                         return NULL;
                 }
                 cache_get(&ipm->h);
         }
+        spin_unlock_bh(&svsk->sk_defer_lock);
         return ipm;
 }
 
@@ -405,9 +410,15 @@ ip_map_cached_put(struct svc_rqst *rqstp, struct ip_map *ipm)
 {
         struct svc_sock *svsk = rqstp->rq_sock;
 
-        if (svsk->sk_sock->type == SOCK_STREAM && svsk->sk_info_authunix == NULL)
-                svsk->sk_info_authunix = ipm;   /* newly cached, keep the reference */
-        else
+        spin_lock_bh(&svsk->sk_defer_lock);
+        if (svsk->sk_sock->type == SOCK_STREAM &&
+            svsk->sk_info_authunix == NULL) {
+                /* newly cached, keep the reference */
+                svsk->sk_info_authunix = ipm;
+                ipm = NULL;
+        }
+        spin_unlock_bh(&svsk->sk_defer_lock);
+        if (ipm)
                 cache_put(&ipm->h, &ip_map_cache);
 }