Re: [PATCH net-next] net: fix up truesize of cloned skb in skb_prepare_for_shift()

[Eric Dumazet]

On Mon, Feb 1, 2021 at 5:04 PM Marco Elver <elver@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxx
> Reported-by: syzbot+7b99aafdcc2eedea6178@xxxxxxxxxxxxxxxxxxxxxxxxx
> Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>

Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>