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SubjectRe: [PATCH v3] ip: fix truesize mismatch in ip fragmentation
On Tue, Sep 21, 2010 at 05:58:25PM +0200, Eric Dumazet wrote:
> Hmm, while looking at git history, I found commit from Patrick
> b2722b1c3a893e (ip_fragment: also adjust skb->truesize for packets not
> owned by a socket)
> As my patch reverts it, we probably want a more polished patch.
>
> (Also port Patrick work to ipv6)
>
> So here is a V3
>
> [PATCH v3] ip: fix truesize mismatch in ip fragmentation
>
> Special care should be taken when slow path is hit in ip_fragment() :
>
> When walking through frags, we transfert truesize ownership from skb to
> frags. Then if we hit a slow_path condition, we must undo this or risk
> uncharging frags->truesize twice, and in the end, having negative socket
> sk_wmem_alloc counter, or even freeing socket sooner than expected.
>
> Many thanks to Nick Bowler, who provided a very clean bug report and
> test program.
>
> Thanks to Jarek for reviewing my first patch and providing a V2
>
> While Nick bisection pointed to commit 2b85a34e911 (net: No more
> expensive sock_hold()/sock_put() on each tx), underlying bug is older
> (2.6.12-rc5)
>
> A side effect is to extend work done in commit b2722b1c3a893e
> (ip_fragment: also adjust skb->truesize for packets not owned by a
> socket) to ipv6 as well.
>
> Reported-and-bisected-by: Nick Bowler <nbowler@elliptictech.com>
> Tested-by: Nick Bowler <nbowler@elliptictech.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> CC: Jarek Poplawski <jarkao2@gmail.com>
> CC: Patrick McHardy <kaber@trash.net>
> ---
> net/ipv4/ip_output.c | 19 +++++++++++++------
> net/ipv6/ip6_output.c | 18 +++++++++++++-----
> 2 files changed, 26 insertions(+), 11 deletions(-)
>
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index 04b6989..a643f7a 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -488,9 +488,8 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
> * we can switch to copy when see the first bad fragment.
> */
> if (skb_has_frags(skb)) {
> - struct sk_buff *frag;
> + struct sk_buff *frag, *frag2;
> int first_len = skb_pagelen(skb);
> - int truesizes = 0;
>
> if (first_len - hlen > mtu ||
> ((first_len - hlen) & 7) ||
> @@ -503,18 +502,18 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
> if (frag->len > mtu ||
> ((frag->len & 7) && frag->next) ||
> skb_headroom(frag) < hlen)
> - goto slow_path;
> + goto slow_path_undo;

Looks better and better to me, except, checkpatch complains about the
(existing) indentation fault here (and later), but I guess you've seen
that?

Jarek P.


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