tcp: fix skb_availroom()
Eric Dumazet [Thu, 14 Mar 2013 05:40:32 +0000 (05:40 +0000)]
[ Upstream commit 16fad69cfe4adbbfa813de516757b87bcae36d93 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/skbuff.h
net/ipv4/tcp.c
net/ipv4/tcp_output.c

index c1bae8d..4aea870 100644 (file)
@@ -479,7 +479,7 @@ struct sk_buff {
        union {
                __u32           mark;
                __u32           dropcount;
-               __u32           avail_size;
+               __u32           reserved_tailroom;
        };
 
        sk_buff_data_t          transport_header;
@@ -1373,7 +1373,10 @@ 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;
 }
 
 /**
index 01870bd..dcb19f5 100644 (file)
@@ -704,7 +704,7 @@ 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);
index 2d27e1a..952f7dd 100644 (file)
@@ -1096,7 +1096,6 @@ 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;