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

[Daniel Borkmann <daniel@iogearbox.net>]

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@mediatek.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@mediatek.com>
>>> Signed-off-by: Lena Wang <lena.wang@mediatek.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