tcp: fix skb_availroom()

Chrome OS team reported a crash on a Pixel ChromeBook in TCP stack :

https://code.google.com/p/chromium/issues/detail?id=182056

commit a21d45726acac (tcp: avoid order-1 allocations on wifi and tx
path) did a poor choice adding an 'avail_size' field to skb, while
what we really needed was a 'reserved_tailroom' one.

It would have avoided commit 22b4a4f22da (tcp: fix retransmit of
partially acked frames) and this commit.

Crash occurs because skb_split() is not aware of the 'avail_size'
management (and should not be aware)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Mukesh Agrawal <quiche@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 821c7f45d2a7357085c757c2309177e443b34990..6f2bb860e0512f2ca078475026a426875bc87c9c 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -500,7 +500,7 @@ struct sk_buff {
        union {
                __u32           mark;
                __u32           dropcount;
-               __u32           avail_size;
+               __u32           reserved_tailroom;
        };
 
        sk_buff_data_t          inner_transport_header;
@@ -1447,7 +1447,10 @@ static inline int skb_tailroom(const struct sk_buff *skb)
  */
 static inline int skb_availroom(const struct sk_buff *skb)
 {
-       return skb_is_nonlinear(skb) ? 0 : skb->avail_size - skb->len;
+       if (skb_is_nonlinear(skb))
+               return 0;
+
+       return skb->end - skb->tail - skb->reserved_tailroom;
 }
 
 /**

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 47e854fcae24dd8c108e93a2b5a22801a68d7232..e22020790709dbde58759c771f47a69e883892e4 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -775,7 +775,7 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp)
                         * Make sure that we have exactly size bytes
                         * available to the caller, no more, no less.
                         */
-                       skb->avail_size = size;
+                       skb->reserved_tailroom = skb->end - skb->tail - size;
                        return skb;
                }
                __kfree_skb(skb);

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index e2b4461074dab715af9c328fd1767f4a5caf8c97..817fbb396bc80077e23b03358355aca6ece6deba 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1298,7 +1298,6 @@ static void __pskb_trim_head(struct sk_buff *skb, int len)
        eat = min_t(int, len, skb_headlen(skb));
        if (eat) {
                __skb_pull(skb, eat);
-               skb->avail_size -= eat;
                len -= eat;
                if (!len)
                        return;