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>

diff --git a/net/sunrpc/svcauth_unix.c b/net/sunrpc/svcauth_unix.c
index 9bae4090254c89f7fb0de7ab25529eac5ea2c90b..2bd23ea2aa8b9cfefc3c771e8444d4dd4d33b8c5 100644 (file)
--- 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);
 }