Messages in this thread | | | Date | Sat, 15 Oct 2022 10:36:46 +0800 | Subject | Re: [PATCH v4,bpf-next] bpf: Don't redirect packets with invalid pkt_len | From | shaozhengchao <> |
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On 2022/10/15 0:55, sdf@google.com wrote: > On 10/14, Lorenz Bauer wrote: >> On Thu, 13 Oct 2022, at 11:44, shaozhengchao wrote: >> > Sorry, I haven't fully understood your intentions yet. >> > Can you explain it more detail? > >> I'll try! Roughly, we do the following: > >> 1. Create a BPF_PROG_TYPE_SOCKET_FILTER program that just returns 0 >> 2. Load the program into the kernel >> 3. Call BPF_PROG_RUN with data_size_in == 14 > >> After your bugfix, it seems like step 3 is rejected due to >> data_size_in == 14. We had to increase data_size_in to 15 to >> avoid this, see [0]. > >> This breaks user space, so it would be great if you could fix this in >> a way that doesn't refuse BPF_PROG_RUN with > > [..] > >> data_size_in == 14. Since I don't understand the original problem very >> well I can't tell you what the best fix is however. > > The problem was that we were able to generate skb with len=0 via > BPF_PROG_RUN. Prohibiting those cases breaks backwards compatibility, so > we either have to: > > a) (preferred?) accept inputs with <14, but maybe internally pad to 14 > bytes to make the core stack happy > b) revert the patch and instead have length checks at runtime; doesn't > seem to > be worth the penalty in the forwarding path because of some corner cases > like these ? > Hi sdf: a) looks better and I'll put up a patch as soon as possible to fix it.
Zhengchao Shao > >> 0: >> https://github.com/cilium/ebpf/commit/a38fb6b5a46ab3b5639ea4d421232a10013596c0 > >> Thanks >> Lorenz
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