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Commit 16fad69c authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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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 a21d4572 (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 22b4a4f2 (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: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarMukesh Agrawal <quiche@chromium.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b701f16d

include/linux/skbuff.h

+5 −2
Original line number Diff line number Diff line
@@ -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;

}



/**

net/ipv4/tcp.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

net/ipv4/tcp_output.c

+0 −1
Original line number Diff line number Diff line
@@ -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;