Messages in this thread | | | Date | Fri, 11 Aug 2023 20:35:35 -0700 | Subject | Re: [PATCH bpf-next] net: Fix slab-out-of-bounds in inet[6]_steal_sock | From | Martin KaFai Lau <> |
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On 8/9/23 10:12 AM, Martin KaFai Lau wrote: > On 8/9/23 8:55 AM, Kuniyuki Iwashima wrote: >> From: Lorenz Bauer <lmb@isovalent.com> >> Date: Wed, 9 Aug 2023 16:08:31 +0100 >>> On Wed, Aug 9, 2023 at 3:39 PM Martin KaFai Lau <martin.lau@linux.dev> wrote: >>>> >>>> On 8/9/23 1:33 AM, Lorenz Bauer wrote: >>>>> Kumar reported a KASAN splat in tcp_v6_rcv: >>>>> >>>>> bash-5.2# ./test_progs -t btf_skc_cls_ingress >>>>> ... >>>>> [ 51.810085] BUG: KASAN: slab-out-of-bounds in tcp_v6_rcv+0x2d7d/0x3440 >>>>> [ 51.810458] Read of size 2 at addr ffff8881053f038c by task >>>>> test_progs/226 >>>>> >>>>> The problem is that inet[6]_steal_sock accesses sk->sk_protocol without >>>>> accounting for request sockets. I added the check to ensure that we only >>>>> every try to perform a reuseport lookup on a supported socket. >>>>> >>>>> It turns out that this isn't necessary at all. struct sock_common contains >>>>> a skc_reuseport flag which indicates whether a socket is part of a >>>> >>>> Does it go back to the earlier discussion >>>> (https://lore.kernel.org/bpf/7188429a-c380-14c8-57bb-9d05d3ba4e5e@linux.dev/) >>>> that the sk->sk_reuseport is 1 from sk_clone for TCP_ESTABLISHED? It works >>>> because there is sk->sk_reuseport"_cb" check going deeper into >>>> reuseport_select_sock() but there is an extra inet6_ehashfn for all >>>> TCP_ESTABLISHED. >>> >>> Sigh, I'd forgotten about this... >>> >>> For the TPROXY TCP replacement use case we sk_assign the SYN to the >>> listener, which creates the reqsk. We can let follow up packets pass >>> without sk_assign since they will match the reqsk and convert to a >>> fullsock via the usual route. At least that is what the test does. I'm >>> not even sure what it means to redirect a random packet into an >>> established TCP socket TBH. It'd probably be dropped? > > It could act like an earlier early-demux for established sk? If the bpf prog has > already looked up an established sk for other needs (eg. reading the sk local > storage), it may as well bpf_sk_assign it to the skb. I don't have a use case > for that but I also don't see why it won't work also. > >>> >>> For UDP, I'm not sure whether we even get into this situation? Doesn't >>> seem like UDP sockets are cloned from each other, so we also shouldn't >>> end up with a reuseport flag set erroneously. >>> >>> Things we could do if necessary: >>> 1. Reset the flag in inet_csk_clone_lock like we do for SOCK_RCU_FREE >> >> I think we can't do this as sk_reuseport is inherited to twsk and used >> in inet_bind_conflict(). >> >> >>> 2. Duplicate the cb check into inet[6]_steal_sock >> >> or 3. Add sk_fullsock() test ? > > yeah, probably adding sk_fullsock() is needed, may be something like(?): > > if (!prefetched || !sk_fullsock(sk)) > return sk;
Friendly ping. Thanks.
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