netdev - Re: [PATCH v3] skbuff: Fix a race between coalescing and releasing SKBs

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Message-ID: <CANn89iLeVKPz05daEPCH+Z5WkPGhJAafFu8z-dSsKW725LtEUA@mail.gmail.com>
Date:   Wed, 12 Apr 2023 16:04:59 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Liang Chen <liangchen.linux@...il.com>
Cc:     kuba@...nel.org, ilias.apalodimas@...aro.org, hawk@...nel.org,
        davem@...emloft.net, pabeni@...hat.com, netdev@...r.kernel.org,
        alexander.duyck@...il.com, linyunsheng@...wei.com
Subject: Re: [PATCH v3] skbuff: Fix a race between coalescing and releasing SKBs

On Tue, Apr 11, 2023 at 4:27 AM Liang Chen <liangchen.linux@...il.com> wrote:
>
> Commit 1effe8ca4e34 ("skbuff: fix coalescing for page_pool fragment
> recycling") allowed coalescing to proceed with non page pool page and page
> pool page when @from is cloned, i.e.
>
> to->pp_recycle    --> false
> from->pp_recycle  --> true
> skb_cloned(from)  --> true
>
> However, it actually requires skb_cloned(@from) to hold true until
> coalescing finishes in this situation. If the other cloned SKB is
> released while the merging is in process, from_shinfo->nr_frags will be
> set to 0 toward the end of the function, causing the increment of frag
> page _refcount to be unexpectedly skipped resulting in inconsistent
> reference counts. Later when SKB(@to) is released, it frees the page
> directly even though the page pool page is still in use, leading to
> use-after-free or double-free errors. So it should be prohibited.
>
> Signed-off-by: Liang Chen <liangchen.linux@...il.com>
> ---
> Changes from v2:
> - switch back to the way v1 works and fix some style issues.
>

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