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From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 2 Feb 2021 18:59:40 +0100
Message-ID: <CANn89iJFvmLctLT99rYn=mCwD8QaJfEaWvawTiVNV4=5dD=Tnw@mail.gmail.com>
Subject: Re: [PATCH net-next] net: fix up truesize of cloned skb in skb_prepare_for_shift()
To:     Marco Elver <elver@google.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Jonathan Lemon <jonathan.lemon@gmail.com>,
        Willem de Bruijn <willemb@google.com>,
        linmiaohe <linmiaohe@huawei.com>,
        Guillaume Nault <gnault@redhat.com>,
        Dongseok Yi <dseok.yi@samsung.com>,
        Yadu Kishore <kyk.segfault@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        netdev <netdev@vger.kernel.org>,
        Alexander Potapenko <glider@google.com>,
        syzbot <syzbot+7b99aafdcc2eedea6178@syzkaller.appspotmail.com>
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On Mon, Feb 1, 2021 at 5:04 PM Marco Elver <elver@google.com> wrote:
>
> Avoid the assumption that ksize(kmalloc(S)) == ksize(kmalloc(S)): when
> cloning an skb, save and restore truesize after pskb_expand_head(). This
> can occur if the allocator decides to service an allocation of the same
> size differently (e.g. use a different size class, or pass the
> allocation on to KFENCE).
>
> Because truesize is used for bookkeeping (such as sk_wmem_queued), a
> modified truesize of a cloned skb may result in corrupt bookkeeping and
> relevant warnings (such as in sk_stream_kill_queues()).
>
> Link: https://lkml.kernel.org/r/X9JR/J6dMMOy1obu@elver.google.com
> Reported-by: syzbot+7b99aafdcc2eedea6178@syzkaller.appspotmail.com
> Suggested-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Marco Elver <elver@google.com>

Signed-off-by: Eric Dumazet <edumazet@google.com>