From: Stanislav Fomichev <sdf@xxxxxxxxxx> [ Upstream commit 07ec7b502800ba9f7b8b15cb01dd6556bb41aaca ] 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? Cc: Eric Dumazet <edumazet@xxxxxxxxxx> Reported-by: syzbot+f635e86ec3fa0a37e019@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx> Link: https://lore.kernel.org/r/20221027225537.353077-1-sdf@xxxxxxxxxx Signed-off-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@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 -- 2.35.1
