tcp: fix crashes in do_tcp_sendpages()

Recent network changes allowed high order pages being used
for skb fragments.

This uncovered a bug in do_tcp_sendpages() which was assuming its caller
provided an array of order-0 page pointers.

We only have to deal with a single page in this function, and its order
is irrelevant.

Reported-by: Willy Tarreau <w@1wt.eu>
Tested-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 9 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 083092e3aed6..e457c7ab2e28 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -830,8 +830,8 @@ static int tcp_send_mss(struct sock *sk, int *size_goal, int flags)
         return mss_now;
 }
 
-static ssize_t do_tcp_sendpages(struct sock *sk, struct page **pages, int poffset,
-                         size_t psize, int flags)
+static ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
+                                size_t size, int flags)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         int mss_now, size_goal;
@@ -858,12 +858,9 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page **pages, int poffse
         if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
                 goto out_err;
 
-        while (psize > 0) {
+        while (size > 0) {
                 struct sk_buff *skb = tcp_write_queue_tail(sk);
-                struct page *page = pages[poffset / PAGE_SIZE];
                 int copy, i;
-                int offset = poffset % PAGE_SIZE;
-                int size = min_t(size_t, psize, PAGE_SIZE - offset);
                 bool can_coalesce;
 
                 if (!tcp_send_head(sk) || (copy = size_goal - skb->len) <= 0) {
@@ -912,8 +909,8 @@ new_segment:
                         TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
 
                 copied += copy;
-                poffset += copy;
-                if (!(psize -= copy))
+                offset += copy;
+                if (!(size -= copy))
                         goto out;
 
                 if (skb->len < size_goal || (flags & MSG_OOB))
@@ -960,7 +957,7 @@ int tcp_sendpage(struct sock *sk, struct page *page, int offset,
                                         flags);
 
         lock_sock(sk);
-        res = do_tcp_sendpages(sk, &page, offset, size, flags);
+        res = do_tcp_sendpages(sk, page, offset, size, flags);
         release_sock(sk);
         return res;
 }