Re: [PATCH net] net: lapb: increase LAPB_HEADER_LEN

[Simon Horman <horms@kernel.org>]

On Wed, Dec 04, 2024 at 02:10:31PM +0000, Eric Dumazet wrote:
> It is unclear if net/lapb code is supposed to be ready for 8021q.
> 
> We can at least avoid crashes like the following :
> 
> skbuff: skb_under_panic: text:ffffffff8aabe1f6 len:24 put:20 head:ffff88802824a400 data:ffff88802824a3fe tail:0x16 end:0x140 dev:nr0.2
> ------------[ cut here ]------------
>  kernel BUG at net/core/skbuff.c:206 !
> Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
> CPU: 1 UID: 0 PID: 5508 Comm: dhcpcd Not tainted 6.12.0-rc7-syzkaller-00144-g66418447d27b #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
>  RIP: 0010:skb_panic net/core/skbuff.c:206 [inline]
>  RIP: 0010:skb_under_panic+0x14b/0x150 net/core/skbuff.c:216
> Code: 0d 8d 48 c7 c6 2e 9e 29 8e 48 8b 54 24 08 8b 0c 24 44 8b 44 24 04 4d 89 e9 50 41 54 41 57 41 56 e8 1a 6f 37 02 48 83 c4 20 90 <0f> 0b 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3
> RSP: 0018:ffffc90002ddf638 EFLAGS: 00010282
> RAX: 0000000000000086 RBX: dffffc0000000000 RCX: 7a24750e538ff600
> RDX: 0000000000000000 RSI: 0000000000000201 RDI: 0000000000000000
> RBP: ffff888034a86650 R08: ffffffff8174b13c R09: 1ffff920005bbe60
> R10: dffffc0000000000 R11: fffff520005bbe61 R12: 0000000000000140
> R13: ffff88802824a400 R14: ffff88802824a3fe R15: 0000000000000016
> FS:  00007f2a5990d740(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000110c2631fd CR3: 0000000029504000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>   skb_push+0xe5/0x100 net/core/skbuff.c:2636
>   nr_header+0x36/0x320 net/netrom/nr_dev.c:69
>   dev_hard_header include/linux/netdevice.h:3148 [inline]
>   vlan_dev_hard_header+0x359/0x480 net/8021q/vlan_dev.c:83
>   dev_hard_header include/linux/netdevice.h:3148 [inline]
>   lapbeth_data_transmit+0x1f6/0x2a0 drivers/net/wan/lapbether.c:257
>   lapb_data_transmit+0x91/0xb0 net/lapb/lapb_iface.c:447
>   lapb_transmit_buffer+0x168/0x1f0 net/lapb/lapb_out.c:149
>  lapb_establish_data_link+0x84/0xd0
>  lapb_device_event+0x4e0/0x670
>   notifier_call_chain+0x19f/0x3e0 kernel/notifier.c:93
>  __dev_notify_flags+0x207/0x400
>   dev_change_flags+0xf0/0x1a0 net/core/dev.c:8922
>   devinet_ioctl+0xa4e/0x1aa0 net/ipv4/devinet.c:1188
>   inet_ioctl+0x3d7/0x4f0 net/ipv4/af_inet.c:1003
>   sock_do_ioctl+0x158/0x460 net/socket.c:1227
>   sock_ioctl+0x626/0x8e0 net/socket.c:1346
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   __do_sys_ioctl fs/ioctl.c:907 [inline]
>   __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: syzbot+fb99d1b0c0f81d94a5e2@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/67506220.050a0220.17bd51.006c.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Simon Horman <horms@kernel.org>