Re: [PATCH v3] ip: fix truesize mismatch in ip fragmentation

[Jarek Poplawski <jarkao2@gmail.com>]

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.