net: fix sk_forward_alloc corruption

On UDP sockets, we must call skb_free_datagram() with socket locked,
or risk sk_forward_alloc corruption. This requirement is not respected
in SUNRPC.

Add a convenient helper, skb_free_datagram_locked() and use it in SUNRPC

Reported-by: Francis Moreau <francis.moro@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 18 insertions, 12 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 6aebfceca3e..bcdd6606f46 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1757,6 +1757,8 @@ extern int	       skb_copy_datagram_const_iovec(const struct sk_buff *from,
                                                      int to_offset,
                                                      int size);
 extern void            skb_free_datagram(struct sock *sk, struct sk_buff *skb);
+extern void            skb_free_datagram_locked(struct sock *sk,
+                                                struct sk_buff *skb);
 extern int             skb_kill_datagram(struct sock *sk, struct sk_buff *skb,
                                          unsigned int flags);
 extern __wsum          skb_checksum(const struct sk_buff *skb, int offset,
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 1c6cf3a1a4f..4ade3011bb3 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -224,6 +224,15 @@ void skb_free_datagram(struct sock *sk, struct sk_buff *skb)
         consume_skb(skb);
         sk_mem_reclaim_partial(sk);
 }
+EXPORT_SYMBOL(skb_free_datagram);
+
+void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
+{
+        lock_sock(sk);
+        skb_free_datagram(sk, skb);
+        release_sock(sk);
+}
+EXPORT_SYMBOL(skb_free_datagram_locked);
 
 /**
  *      skb_kill_datagram - Free a datagram skbuff forcibly
@@ -752,5 +761,4 @@ unsigned int datagram_poll(struct file *file, struct socket *sock,
 EXPORT_SYMBOL(datagram_poll);
 EXPORT_SYMBOL(skb_copy_and_csum_datagram_iovec);
 EXPORT_SYMBOL(skb_copy_datagram_iovec);
-EXPORT_SYMBOL(skb_free_datagram);
 EXPORT_SYMBOL(skb_recv_datagram);
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index d0d436d6216..0fa9f70e4b1 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -999,9 +999,7 @@ try_again:
                 err = ulen;
 
 out_free:
-        lock_sock(sk);
-        skb_free_datagram(sk, skb);
-        release_sock(sk);
+        skb_free_datagram_locked(sk, skb);
 out:
         return err;
 
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 3a60f12b34e..cf538ed5ef6 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -288,9 +288,7 @@ try_again:
                 err = ulen;
 
 out_free:
-        lock_sock(sk);
-        skb_free_datagram(sk, skb);
-        release_sock(sk);
+        skb_free_datagram_locked(sk, skb);
 out:
         return err;
 
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index ccc5e83cae5..1c246a4f491 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -111,7 +111,7 @@ static void svc_release_skb(struct svc_rqst *rqstp)
                 rqstp->rq_xprt_ctxt = NULL;
 
                 dprintk("svc: service %p, releasing skb %p\n", rqstp, skb);
-                skb_free_datagram(svsk->sk_sk, skb);
+                skb_free_datagram_locked(svsk->sk_sk, skb);
         }
 }
 
@@ -578,7 +578,7 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
                                 "svc: received unknown control message %d/%d; "
                                 "dropping RPC reply datagram\n",
                                         cmh->cmsg_level, cmh->cmsg_type);
-                skb_free_datagram(svsk->sk_sk, skb);
+                skb_free_datagram_locked(svsk->sk_sk, skb);
                 return 0;
         }
 
@@ -588,18 +588,18 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
                 if (csum_partial_copy_to_xdr(&rqstp->rq_arg, skb)) {
                         local_bh_enable();
                         /* checksum error */
-                        skb_free_datagram(svsk->sk_sk, skb);
+                        skb_free_datagram_locked(svsk->sk_sk, skb);
                         return 0;
                 }
                 local_bh_enable();
-                skb_free_datagram(svsk->sk_sk, skb);
+                skb_free_datagram_locked(svsk->sk_sk, skb);
         } else {
                 /* we can use it in-place */
                 rqstp->rq_arg.head[0].iov_base = skb->data +
                         sizeof(struct udphdr);
                 rqstp->rq_arg.head[0].iov_len = len;
                 if (skb_checksum_complete(skb)) {
-                        skb_free_datagram(svsk->sk_sk, skb);
+                        skb_free_datagram_locked(svsk->sk_sk, skb);
                         return 0;
                 }
                 rqstp->rq_xprt_ctxt = skb;