In some situation vlan packets do not have ethernet headers. One example is packets from tun devices. Users can specify vlan protocol in tun_pi field instead of IP protocol, and skb_vlan_untag() attempts to untag such packets. skb_vlan_untag() (more precisely, skb_reorder_vlan_header() called by it) however did not expect packets without ethernet headers, so in such a case size argument for memmove() underflowed and triggered crash. ==== BUG: unable to handle kernel paging request at ffff8801cccb8000 IP: __memmove+0x24/0x1a0 arch/x86/lib/memmove_64.S:43 PGD 9cee067 P4D 9cee067 PUD 1d9401063 PMD 1cccb7063 PTE 2810100028101 Oops: 000b [#1] SMP KASAN Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: CPU: 1 PID: 17663 Comm: syz-executor2 Not tainted 4.16.0-rc7+ #368 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:__memmove+0x24/0x1a0 arch/x86/lib/memmove_64.S:43 RSP: 0018:ffff8801cc046e28 EFLAGS: 00010287 RAX: ffff8801ccc244c4 RBX: fffffffffffffffe RCX: fffffffffff6c4c2 RDX: fffffffffffffffe RSI: ffff8801cccb7ffc RDI: ffff8801cccb8000 RBP: ffff8801cc046e48 R08: ffff8801ccc244be R09: ffffed0039984899 R10: 0000000000000001 R11: ffffed0039984898 R12: ffff8801ccc244c4 R13: ffff8801ccc244c0 R14: ffff8801d96b7c06 R15: ffff8801d96b7b40 FS: 00007febd562d700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff8801cccb8000 CR3: 00000001ccb2f006 CR4: 00000000001606e0 DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600 Call Trace: memmove include/linux/string.h:360 [inline] skb_reorder_vlan_header net/core/skbuff.c:5031 [inline] skb_vlan_untag+0x470/0xc40 net/core/skbuff.c:5061 __netif_receive_skb_core+0x119c/0x3460 net/core/dev.c:4460 __netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4627 netif_receive_skb_internal+0x10b/0x670 net/core/dev.c:4701 netif_receive_skb+0xae/0x390 net/core/dev.c:4725 tun_rx_batched.isra.50+0x5ee/0x870 drivers/net/tun.c:1555 tun_get_user+0x299e/0x3c20 drivers/net/tun.c:1962 tun_chr_write_iter+0xb9/0x160 drivers/net/tun.c:1990 call_write_iter include/linux/fs.h:1782 [inline] new_sync_write fs/read_write.c:469 [inline] __vfs_write+0x684/0x970 fs/read_write.c:482 vfs_write+0x189/0x510 fs/read_write.c:544 SYSC_write fs/read_write.c:589 [inline] SyS_write+0xef/0x220 fs/read_write.c:581 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7 RIP: 0033:0x454879 RSP: 002b:00007febd562cc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007febd562d6d4 RCX: 0000000000454879 RDX: 0000000000000157 RSI: 0000000020000180 RDI: 0000000000000014 RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 00000000000006b0 R14: 00000000006fc120 R15: 0000000000000000 Code: 90 90 90 90 90 90 90 48 89 f8 48 83 fa 20 0f 82 03 01 00 00 48 39 fe 7d 0f 49 89 f0 49 01 d0 49 39 f8 0f 8f 9f 00 00 00 48 89 d1 <f3> a4 c3 48 81 fa a8 02 00 00 72 05 40 38 fe 74 3b 48 83 ea 20 RIP: __memmove+0x24/0x1a0 arch/x86/lib/memmove_64.S:43 RSP: ffff8801cc046e28 CR2: ffff8801cccb8000 ==== We don't need to copy headers for packets which do not have preceding headers of vlan headers, so skip memmove() in that case.
Unified · Split
| @@ -5028,8 +5028,10 @@ static struct sk_buff *skb_reorder_vlan_header(struct sk_buff *skb) · 5027 unmodified lines | |||
| 5028 | } | 5028 | } |
| 5029 | 5029 | ||
| 5030 | mac_len = skb->data - skb_mac_header(skb); | 5030 | mac_len = skb->data - skb_mac_header(skb); |
| 5031 | memmove(skb_mac_header(skb) + VLAN_HLEN, skb_mac_header(skb), | 5031 | if (likely(mac_len > VLAN_HLEN + ETH_TLEN)) { |
| 5032 | mac_len - VLAN_HLEN - ETH_TLEN); | 5032 | memmove(skb_mac_header(skb) + VLAN_HLEN, skb_mac_header(skb), |
| 5033 | mac_len - VLAN_HLEN - ETH_TLEN); | ||
| 5034 | } | ||
| 5033 | skb->mac_header += VLAN_HLEN; | 5035 | skb->mac_header += VLAN_HLEN; |
| 5034 | return skb; | 5036 | return skb; |
| 5035 | } | 5037 | } |