netdev - Re: [PATCH net] udp: fix segmentation crash for GRO packet without fraglist

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Date: Fri, 26 Apr 2024 23:08:11 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Lena Wang (王娜) <Lena.Wang@...iatek.com>,
 "maze@...gle.com" <maze@...gle.com>,
 "willemdebruijn.kernel@...il.com" <willemdebruijn.kernel@...il.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
 "steffen.klassert@...unet.com" <steffen.klassert@...unet.com>,
 "kuba@...nel.org" <kuba@...nel.org>,
 Shiming Cheng (成诗明)
 <Shiming.Cheng@...iatek.com>, "pabeni@...hat.com" <pabeni@...hat.com>,
 "edumazet@...gle.com" <edumazet@...gle.com>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
 "davem@...emloft.net" <davem@...emloft.net>,
 "yan@...udflare.com" <yan@...udflare.com>
Subject: Re: [PATCH net] udp: fix segmentation crash for GRO packet without
 fraglist

On 4/26/24 11:52 AM, Lena Wang (王娜) wrote:
[...]
>>>  From 301da5c9d65652bac6091d4cd64b751b3338f8bb Mon Sep 17 00:00:00
>> 2001
>>> From: Shiming Cheng <shiming.cheng@...iatek.com>
>>> Date: Wed, 24 Apr 2024 13:42:35 +0800
>>> Subject: [PATCH net] net: prevent BPF pulling SKB_GSO_FRAGLIST skb
>>>
>>> A SKB_GSO_FRAGLIST skb can't be pulled data
>>> from its fraglist as it may result an invalid
>>> segmentation or kernel exception.
>>>
>>> For such structured skb we limit the BPF pulling
>>> data length smaller than skb_headlen() and return
>>> error if exceeding.
>>>
>>> Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.")
>>> Signed-off-by: Shiming Cheng <shiming.cheng@...iatek.com>
>>> Signed-off-by: Lena Wang <lena.wang@...iatek.com>
>>> ---
>>>   net/core/filter.c | 5 +++++
>>>   1 file changed, 5 insertions(+)
>>>
>>> diff --git a/net/core/filter.c b/net/core/filter.c
>>> index 8adf95765cdd..8ed4d5d87167 100644
>>> --- a/net/core/filter.c
>>> +++ b/net/core/filter.c
>>> @@ -1662,6 +1662,11 @@ static DEFINE_PER_CPU(struct bpf_scratchpad,
>>> bpf_sp);
>>>   static inline int __bpf_try_make_writable(struct sk_buff *skb,
>>>     unsigned int write_len)
>>>   {
>>> +if (skb_is_gso(skb) &&
>>> +    (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST) &&
>>> +     write_len > skb_headlen(skb)) {
>>> +return -ENOMEM;
>>> +}
>>>   return skb_ensure_writable(skb, write_len);

Dumb question, but should this guard be more generically part of skb_ensure_writable()
internals, presumably that would be inside pskb_may_pull_reason(), or only if we ever
see more code instances similar to this?

Thanks,
Daniel