[TCP]: Fix sk_forward_alloc underflow in tcp_sendmsg

I've finally found a potential cause of the sk_forward_alloc underflows
that people have been reporting sporadically.

When tcp_sendmsg tacks on extra bits to an existing TCP_PAGE we don't
check sk_forward_alloc even though a large amount of time may have
elapsed since we allocated the page.  In the mean time someone could've
come along and liberated packets and reclaimed sk_forward_alloc memory.

This patch makes tcp_sendmsg check sk_forward_alloc every time as we
do in do_tcp_sendpages.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/sock.h b/include/net/sock.h
index e51e626e9af183354544b6aac0057ed071345029..cf628261da521cba025d7401abb3d52900cb35ee 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1232,9 +1232,8 @@ static inline struct page *sk_stream_alloc_page(struct sock *sk)
 {
        struct page *page = NULL;
 
-       if (sk_stream_wmem_schedule(sk, PAGE_SIZE))
-               page = alloc_pages(sk->sk_allocation, 0);
-       else {
+       page = alloc_pages(sk->sk_allocation, 0);
+       if (!page) {
                sk->sk_prot->enter_memory_pressure();
                sk_stream_moderate_sndbuf(sk);
        }

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 854f6d0c4bb3de698b3028c11327322172f85412..cbcc9fc4778365add8f53e6d63667d4ef6e74184 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -769,19 +769,23 @@ new_segment:
                                        if (off == PAGE_SIZE) {
                                                put_page(page);
                                                TCP_PAGE(sk) = page = NULL;
+                                               TCP_OFF(sk) = off = 0;
                                        }
-                               }
+                               } else
+                                       BUG_ON(off);
+
+                               if (copy > PAGE_SIZE - off)
+                                       copy = PAGE_SIZE - off;
+
+                               if (!sk_stream_wmem_schedule(sk, copy))
+                                       goto wait_for_memory;
 
                                if (!page) {
                                        /* Allocate new cache page. */
                                        if (!(page = sk_stream_alloc_page(sk)))
                                                goto wait_for_memory;
-                                       off = 0;
                                }
 
-                               if (copy > PAGE_SIZE - off)
-                                       copy = PAGE_SIZE - off;
-
                                /* Time to copy data. We are close to
                                 * the end! */
                                err = skb_copy_to_page(sk, from, skb, page,