Messages in this thread | | | Date | Wed, 29 Nov 2023 14:18:46 +0100 | From | Florian Westphal <> | Subject | Re: [PATCH net] net/netfilter: bpf: avoid leakage of skb |
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D. Wythe <alibuda@linux.alibaba.com> wrote: > From: "D. Wythe" <alibuda@linux.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.
> 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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