linux-kernel - Re: [PATCH net v10] skb_expand_head() adjust skb->truesize incorrectly

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Message-ID: <a55b298d-703f-d204-d425-a1d0704b2bb8@gmail.com>
Date:   Fri, 22 Oct 2021 12:32:35 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Vasily Averin <vvs@...tuozzo.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Julian Wiedmann <jwi@...ux.ibm.com>,
        Christoph Paasch <christoph.paasch@...il.com>,
        linux-kernel@...r.kernel.org, kernel@...nvz.org
Subject: Re: [PATCH net v10] skb_expand_head() adjust skb->truesize
 incorrectly



On 10/22/21 3:28 AM, Vasily Averin wrote:
> Christoph Paasch reports [1] about incorrect skb->truesize
> after skb_expand_head() call in ip6_xmit.
> This may happen because of two reasons:
> - skb_set_owner_w() for newly cloned skb is called too early,
> before pskb_expand_head() where truesize is adjusted for (!skb-sk) case.
> - pskb_expand_head() does not adjust truesize in (skb->sk) case.
> In this case sk->sk_wmem_alloc should be adjusted too.
> 
> [1] https://lkml.org/lkml/2021/8/20/1082
> 
> Fixes: f1260ff15a71 ("skbuff: introduce skb_expand_head()")
> Fixes: 2d85a1b31dde ("ipv6: ip6_finish_output2: set sk into newly allocated nskb")
> Reported-by: Christoph Paasch <christoph.paasch@...il.com>
> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
> ---
> v10: is_skb_wmem() was moved into separate header (it depends on net/tcp.h)
>      use it after pskb_expand_head() insted of strange sock_edemux check

SGTM, thanks !

Reviewed-by: Eric Dumazet <edumazet@...gle.com>