From: Christoph Paasch <christoph.paasch@gmail.com>
To: Marco Elver <elver@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
kasan-dev@googlegroups.com, David Miller <davem@davemloft.net>,
kuba@kernel.org, Jonathan Lemon <jonathan.lemon@gmail.com>,
Willem de Bruijn <willemb@google.com>,
linmiaohe@huawei.com, gnault@redhat.com, dseok.yi@samsung.com,
kyk.segfault@gmail.com, Al Viro <viro@zeniv.linux.org.uk>,
netdev <netdev@vger.kernel.org>,
glider@google.com,
syzbot+7b99aafdcc2eedea6178@syzkaller.appspotmail.com,
Eric Dumazet <edumazet@google.com>
Subject: Re: [PATCH net-next] net: fix up truesize of cloned skb in skb_prepare_for_shift()
Date: Mon, 1 Feb 2021 08:50:16 -0800 [thread overview]
Message-ID: <CALMXkpYaEEv6u1oY3cFSznWsGCeiFRxRJRDS0j+gZxAc8VESZg@mail.gmail.com> (raw)
In-Reply-To: <20210201160420.2826895-1-elver@google.com>
On Mon, Feb 1, 2021 at 8:09 AM 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>
> ---
> net/core/skbuff.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 2af12f7e170c..3787093239f5 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3289,7 +3289,19 @@ EXPORT_SYMBOL(skb_split);
> */
> static int skb_prepare_for_shift(struct sk_buff *skb)
> {
> - return skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
> + int ret = 0;
> +
> + if (skb_cloned(skb)) {
> + /* Save and restore truesize: pskb_expand_head() may reallocate
> + * memory where ksize(kmalloc(S)) != ksize(kmalloc(S)), but we
> + * cannot change truesize at this point.
> + */
> + unsigned int save_truesize = skb->truesize;
> +
> + ret = pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
> + skb->truesize = save_truesize;
> + }
> + return ret;
just a few days ago we found out that this also fixes a syzkaller
issue on MPTCP (https://github.com/multipath-tcp/mptcp_net-next/issues/136).
I confirmed that this patch fixes the issue for us as well:
Tested-by: Christoph Paasch <christoph.paasch@gmail.com>
> }
>
> /**
>
> base-commit: 14e8e0f6008865d823a8184a276702a6c3cbef3d
> --
> 2.30.0.365.g02bc693789-goog
>
next prev parent reply other threads:[~2021-02-01 16:51 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-01 16:04 [PATCH net-next] net: fix up truesize of cloned skb in skb_prepare_for_shift() Marco Elver
2021-02-01 16:50 ` Christoph Paasch [this message]
2021-02-01 17:33 ` Marco Elver
2021-02-01 17:58 ` Eric Dumazet
2021-02-02 16:58 ` Christoph Paasch
2021-02-02 17:59 ` Eric Dumazet
2021-02-02 18:34 ` Marco Elver
2021-02-03 2:00 ` patchwork-bot+netdevbpf
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