On Tue, Nov 1, 2022 at 1:28 PM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote: > > On 10/27/22 3:55 PM, Stanislav Fomichev wrote: > > syzkaller managed to trigger another case where skb->len == 0 > > when we enter __dev_queue_xmit: > > > > WARNING: CPU: 0 PID: 2470 at include/linux/skbuff.h:2576 skb_assert_len include/linux/skbuff.h:2576 [inline] > > WARNING: CPU: 0 PID: 2470 at include/linux/skbuff.h:2576 __dev_queue_xmit+0x2069/0x35e0 net/core/dev.c:4295 > > > > Call Trace: > > dev_queue_xmit+0x17/0x20 net/core/dev.c:4406 > > __bpf_tx_skb net/core/filter.c:2115 [inline] > > __bpf_redirect_no_mac net/core/filter.c:2140 [inline] > > __bpf_redirect+0x5fb/0xda0 net/core/filter.c:2163 > > ____bpf_clone_redirect net/core/filter.c:2447 [inline] > > bpf_clone_redirect+0x247/0x390 net/core/filter.c:2419 > > bpf_prog_48159a89cb4a9a16+0x59/0x5e > > bpf_dispatcher_nop_func include/linux/bpf.h:897 [inline] > > __bpf_prog_run include/linux/filter.h:596 [inline] > > bpf_prog_run include/linux/filter.h:603 [inline] > > bpf_test_run+0x46c/0x890 net/bpf/test_run.c:402 > > bpf_prog_test_run_skb+0xbdc/0x14c0 net/bpf/test_run.c:1170 > > bpf_prog_test_run+0x345/0x3c0 kernel/bpf/syscall.c:3648 > > __sys_bpf+0x43a/0x6c0 kernel/bpf/syscall.c:5005 > > __do_sys_bpf kernel/bpf/syscall.c:5091 [inline] > > __se_sys_bpf kernel/bpf/syscall.c:5089 [inline] > > __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5089 > > do_syscall_64+0x54/0x70 arch/x86/entry/common.c:48 > > entry_SYSCALL_64_after_hwframe+0x61/0xc6 > > > > The reproducer doesn't really reproduce outside of syzkaller > > environment, so I'm taking a guess here. It looks like we > > do generate correct ETH_HLEN-sized packet, but we redirect > > the packet to the tunneling device. Before we do so, we > > __skb_pull l2 header and arrive again at skb->len == 0. > > Doesn't seem like we can do anything better than having > > an explicit check after __skb_pull? > hmm... I recall there was similar report but I didn't follow those earlier fixes > and discussion. Not sure if this has been considered: > If this skb can only happen in the bpf_prog_test_run (?), > how about ensure that the skb will at least have some header after l2 header in > bpf_prog_test_run_skb(). Adding some headers/bytes if the data_size_in does not > have it. This may break some external test cases that somehow has no l3/4? > test_progs should be mostly fine considering they are using the pkt_v[46] in > network_helpers.h. For the previous issue we've added "skb->len != 0" check which works for the cases that remove l2. For the ones that don't, I think you're right, and checking at the time of bpf_prog_test_run_skb can probably be enough, lemme try (require ETH_HLEN+1 vs ETH_HLEN). For some reason I was under the impression that Lorenz changed the size from 0 to 14 [0], but he went from 14 to 15, so we won't break at least cilium again.. CC'd him just in case. 0: https://github.com/cilium/ebpf/pull/788 > Adding some headers/bytes if the data_size_in does not have it. > This may break some external test cases that somehow has no l3/4? Yeah, idk, this seems like a last resort? I'd prefer to explicitly fail and communicate it back to the user than slap some extra byte and then fail in some other place unpredictably? > > Cc: Eric Dumazet <edumazet@xxxxxxxxxx> > > Reported-by: syzbot+f635e86ec3fa0a37e019@xxxxxxxxxxxxxxxxxxxxxxxxx > > Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx> > > --- > > net/core/filter.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index bb0136e7a8e4..cb3b635e35be 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -2126,6 +2126,10 @@ static int __bpf_redirect_no_mac(struct sk_buff *skb, struct net_device *dev, > > > > if (mlen) { > > __skb_pull(skb, mlen); > > + if (unlikely(!skb->len)) { > > + kfree_skb(skb); > > + return -ERANGE; > > + } > > > > /* At ingress, the mac header has already been pulled once. > > * At egress, skb_pospull_rcsum has to be done in case that >
