CVE-2022-50253

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> bpf: make sure skb-&gt;len != 0 when redirecting to a tunneling device<br /> <br /> syzkaller managed to trigger another case where skb-&gt;len == 0<br /> when we enter __dev_queue_xmit:<br /> <br /> WARNING: CPU: 0 PID: 2470 at include/linux/skbuff.h:2576 skb_assert_len include/linux/skbuff.h:2576 [inline]<br /> WARNING: CPU: 0 PID: 2470 at include/linux/skbuff.h:2576 __dev_queue_xmit+0x2069/0x35e0 net/core/dev.c:4295<br /> <br /> Call Trace:<br /> dev_queue_xmit+0x17/0x20 net/core/dev.c:4406<br /> __bpf_tx_skb net/core/filter.c:2115 [inline]<br /> __bpf_redirect_no_mac net/core/filter.c:2140 [inline]<br /> __bpf_redirect+0x5fb/0xda0 net/core/filter.c:2163<br /> ____bpf_clone_redirect net/core/filter.c:2447 [inline]<br /> bpf_clone_redirect+0x247/0x390 net/core/filter.c:2419<br /> bpf_prog_48159a89cb4a9a16+0x59/0x5e<br /> bpf_dispatcher_nop_func include/linux/bpf.h:897 [inline]<br /> __bpf_prog_run include/linux/filter.h:596 [inline]<br /> bpf_prog_run include/linux/filter.h:603 [inline]<br /> bpf_test_run+0x46c/0x890 net/bpf/test_run.c:402<br /> bpf_prog_test_run_skb+0xbdc/0x14c0 net/bpf/test_run.c:1170<br /> bpf_prog_test_run+0x345/0x3c0 kernel/bpf/syscall.c:3648<br /> __sys_bpf+0x43a/0x6c0 kernel/bpf/syscall.c:5005<br /> __do_sys_bpf kernel/bpf/syscall.c:5091 [inline]<br /> __se_sys_bpf kernel/bpf/syscall.c:5089 [inline]<br /> __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5089<br /> do_syscall_64+0x54/0x70 arch/x86/entry/common.c:48<br /> entry_SYSCALL_64_after_hwframe+0x61/0xc6<br /> <br /> The reproducer doesn&amp;#39;t really reproduce outside of syzkaller<br /> environment, so I&amp;#39;m taking a guess here. It looks like we<br /> do generate correct ETH_HLEN-sized packet, but we redirect<br /> the packet to the tunneling device. Before we do so, we<br /> __skb_pull l2 header and arrive again at skb-&gt;len == 0.<br /> Doesn&amp;#39;t seem like we can do anything better than having<br /> an explicit check after __skb_pull?