In the Linux kernel, the following vulnerability has been resolved:

net: hsr: avoid potential out-of-bound access in fill_frame_info()

syzbot is able to feed a packet with 14 bytes, pretending
it is a vlan one.

Since fill_frame_info() is relying on skb->mac_len already,
extend the check to cover this case.

BUG: KMSAN: uninit-value in fill_frame_info net/hsr/hsr_forward.c:709 [inline]
 BUG: KMSAN: uninit-value in hsr_forward_skb+0x9ee/0x3b10 net/hsr/hsr_forward.c:724
  fill_frame_info net/hsr/hsr_forward.c:709 [inline]
  hsr_forward_skb+0x9ee/0x3b10 net/hsr/hsr_forward.c:724
  hsr_dev_xmit+0x2f0/0x350 net/hsr/hsr_device.c:235
  __netdev_start_xmit include/linux/netdevice.h:5002 [inline]
  netdev_start_xmit include/linux/netdevice.h:5011 [inline]
  xmit_one net/core/dev.c:3590 [inline]
  dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3606
  __dev_queue_xmit+0x366a/0x57d0 net/core/dev.c:4434
  dev_queue_xmit include/linux/netdevice.h:3168 [inline]
  packet_xmit+0x9c/0x6c0 net/packet/af_packet.c:276
  packet_snd net/packet/af_packet.c:3146 [inline]
  packet_sendmsg+0x91ae/0xa6f0 net/packet/af_packet.c:3178
  sock_sendmsg_nosec net/socket.c:711 [inline]
  __sock_sendmsg+0x30f/0x380 net/socket.c:726
  __sys_sendto+0x594/0x750 net/socket.c:2197
  __do_sys_sendto net/socket.c:2204 [inline]
  __se_sys_sendto net/socket.c:2200 [inline]
  __x64_sys_sendto+0x125/0x1d0 net/socket.c:2200
  x64_sys_call+0x346a/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:45
  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
  do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
  slab_post_alloc_hook mm/slub.c:4091 [inline]
  slab_alloc_node mm/slub.c:4134 [inline]
  kmem_cache_alloc_node_noprof+0x6bf/0xb80 mm/slub.c:4186
  kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:587
  __alloc_skb+0x363/0x7b0 net/core/skbuff.c:678
  alloc_skb include/linux/skbuff.h:1323 [inline]
  alloc_skb_with_frags+0xc8/0xd00 net/core/skbuff.c:6612
  sock_alloc_send_pskb+0xa81/0xbf0 net/core/sock.c:2881
  packet_alloc_skb net/packet/af_packet.c:2995 [inline]
  packet_snd net/packet/af_packet.c:3089 [inline]
  packet_sendmsg+0x74c6/0xa6f0 net/packet/af_packet.c:3178
  sock_sendmsg_nosec net/socket.c:711 [inline]
  __sock_sendmsg+0x30f/0x380 net/socket.c:726
  __sys_sendto+0x594/0x750 net/socket.c:2197
  __do_sys_sendto net/socket.c:2204 [inline]
  __se_sys_sendto net/socket.c:2200 [inline]
  __x64_sys_sendto+0x125/0x1d0 net/socket.c:2200
  x64_sys_call+0x346a/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:45
  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
  do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f