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Message-ID: <aa83bf32-789f-fec2-ea42-74b0ae05426e@linux.alibaba.com>
Date: Wed, 29 Nov 2023 22:42:23 +0800
From: "D. Wythe" <alibuda@...ux.alibaba.com>
To: Florian Westphal <fw@...len.de>
Cc: pablo@...filter.org, kadlec@...filter.org, bpf@...r.kernel.org,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
coreteam@...filter.org, netfilter-devel@...r.kernel.org,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com, ast@...nel.org
Subject: Re: [PATCH net] net/netfilter: bpf: avoid leakage of skb
On 11/29/23 9:18 PM, Florian Westphal wrote:
> D. Wythe <alibuda@...ux.alibaba.com> wrote:
>> From: "D. Wythe" <alibuda@...ux.alibaba.com>
>>
>> A malicious eBPF program can interrupt the subsequent processing of
>> a skb by returning an exceptional retval, and no one will be responsible
>> for releasing the very skb.
> How? The bpf verifier is supposed to reject nf bpf programs that
> return a value other than accept or drop.
>
> If this is a real bug, please also figure out why
> 006c0e44ed92 ("selftests/bpf: add missing netfilter return value and ctx access tests")
> failed to catch it.
Hi Florian,
You are right, i make a mistake.. , it's not a bug..
And my origin intention was to allow ebpf progs to return NF_STOLEN, we
are trying to modify some netfilter modules via ebpf,
and some scenarios require the use of NF_STOLEN, but from your
description, it seems that at least currently,
you do not want to return NF_STOLEN, until there is a helper for
sonsume_skb(), right ?
Again, very sorry to bother you.
Best wishes,
D. Wythe.
>> Moreover, normal programs can also have the demand to return NF_STOLEN,
> No, this should be disallowed already.
>
>> net/netfilter/nf_bpf_link.c | 19 ++++++++++++++++++-
>> 1 file changed, 18 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c
>> index e502ec0..03c47d6 100644
>> --- a/net/netfilter/nf_bpf_link.c
>> +++ b/net/netfilter/nf_bpf_link.c
>> @@ -12,12 +12,29 @@ static unsigned int nf_hook_run_bpf(void *bpf_prog, struct sk_buff *skb,
>> const struct nf_hook_state *s)
>> {
>> const struct bpf_prog *prog = bpf_prog;
>> + unsigned int verdict;
>> struct bpf_nf_ctx ctx = {
>> .state = s,
>> .skb = skb,
>> };
>>
>> - return bpf_prog_run(prog, &ctx);
>> + verdict = bpf_prog_run(prog, &ctx);
>> + switch (verdict) {
>> + case NF_STOLEN:
>> + consume_skb(skb);
>> + fallthrough;
> This can't be right. STOLEN really means STOLEN (free'd,
> redirected, etc, "skb" MUST be "leaked".
>
> Which is also why the bpf program is not allowed to return it.
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