Bug#782515: [PATCH stable 3.10-3.16] tcp: Fix crash in TCP Fast Open
On Wed, Apr 15, 2015 at 07:00:32PM +0100, Ben Hutchings wrote:
> Commit 355a901e6cf1 ("tcp: make connect() mem charging friendly")
> changed tcp_send_syn_data() to perform an open-coded copy of the 'syn'
> skb rather than using skb_copy_expand().
>
> The open-coded copy does not cover the skb_shared_info::gso_segs
> field, so in the new skb it is left set to 0. When this commit was
> backported into stable branches between 3.10.y and 3.16.7-ckty
> inclusive, it triggered the BUG() in tcp_transmit_skb().
>
> Since Linux 3.18 the GSO segment count is kept in the
> tcp_skb_cb::tcp_gso_segs field and tcp_send_syn_data() does copy the
> tcp_skb_cb structure to the new skb, so mainline and newer stable
> branches are not affected.
>
> Set skb_shared_info::gso_segs to the correct value of 1.
>
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Thanks a lot, Ben. I'll queue this for the next 3.16 kernel release.
Cheers,
--
Luís
> ---
> net/ipv4/tcp_output.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index d5457e4..1ea0a07 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2992,6 +2992,7 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
> goto fallback;
> syn_data->ip_summed = CHECKSUM_PARTIAL;
> memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
> + skb_shinfo(syn_data)->gso_segs = 1;
> if (unlikely(memcpy_fromiovecend(skb_put(syn_data, space),
> fo->data->msg_iov, 0, space))) {
> kfree_skb(syn_data);
>
> --
> Ben Hutchings
> Editing code like this is akin to sticking plasters on the bleeding stump
> of a severed limb. - me, 29 June 1999
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