net/tcp: null-ptr-deref in __inet_lookup_listener/inet_exact_dif_match

[Andrey Konovalov]

Hi,

I've got the following error report while running the syzkaller fuzzer:

general protection fault: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 648 Comm: syz-executor Not tainted 4.9.0-rc3+ #333
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff8800398c4480 task.stack: ffff88003b468000
RIP: 0010:[<ffffffff83091106>] [< inline >]
inet_exact_dif_match include/net/tcp.h:808
RIP: 0010:[<ffffffff83091106>] [<ffffffff83091106>]
__inet_lookup_listener+0xb6/0x500 net/ipv4/inet_hashtables.c:219
RSP: 0018:ffff88003b46f270 EFLAGS: 00010202
RAX: 0000000000000004 RBX: 0000000000004242 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffc90000e3c000 RDI: 0000000000000054
RBP: ffff88003b46f2d8 R08: 0000000000004000 R09: ffffffff830910e7
R10: 0000000000000000 R11: 000000000000000a R12: ffffffff867fa0c0
R13: 0000000000004242 R14: 0000000000000003 R15: dffffc0000000000
FS: 00007fb135881700(0000) GS:ffff88003ec00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020cc3000 CR3: 000000006d56a000 CR4: 00000000000006f0
Stack:
0000000000000000 000000000601a8c0 0000000000000000 ffffffff00004242
424200003b9083c2 ffff88003def4041 ffffffff84e7e040 0000000000000246
ffff88003a0911c0 0000000000000000 ffff88003a091298 ffff88003b9083ae
Call Trace:
[<ffffffff831100f4>] tcp_v4_send_reset+0x584/0x1700 net/ipv4/tcp_ipv4.c:643
[<ffffffff83115b1b>] tcp_v4_rcv+0x198b/0x2e50 net/ipv4/tcp_ipv4.c:1718
[<ffffffff83069d22>] ip_local_deliver_finish+0x332/0xad0
net/ipv4/ip_input.c:216
[< inline >] NF_HOOK_THRESH include/linux/netfilter.h:232
[< inline >] NF_HOOK include/linux/netfilter.h:255
[<ffffffff8306abd2>] ip_local_deliver+0x1c2/0x4b0 net/ipv4/ip_input.c:257
[< inline >] dst_input include/net/dst.h:507
[<ffffffff83068500>] ip_rcv_finish+0x750/0x1c40 net/ipv4/ip_input.c:396
[< inline >] NF_HOOK_THRESH include/linux/netfilter.h:232
[< inline >] NF_HOOK include/linux/netfilter.h:255
[<ffffffff8306b82f>] ip_rcv+0x96f/0x12f0 net/ipv4/ip_input.c:487
[<ffffffff82bd9fb7>] __netif_receive_skb_core+0x1897/0x2a50 net/core/dev.c:4213
[<ffffffff82bdb19a>] __netif_receive_skb+0x2a/0x170 net/core/dev.c:4251
[<ffffffff82bdb493>] netif_receive_skb_internal+0x1b3/0x390 net/core/dev.c:4279
[<ffffffff82bdb6b8>] netif_receive_skb+0x48/0x250 net/core/dev.c:4303
[<ffffffff8241fc75>] tun_get_user+0xbd5/0x28a0 drivers/net/tun.c:1308
[<ffffffff82421b5a>] tun_chr_write_iter+0xda/0x190 drivers/net/tun.c:1332
[< inline >] new_sync_write fs/read_write.c:499
[<ffffffff8151bd44>] __vfs_write+0x334/0x570 fs/read_write.c:512
[<ffffffff8151f85b>] vfs_write+0x17b/0x500 fs/read_write.c:560
[< inline >] SYSC_write fs/read_write.c:607
[<ffffffff81523184>] SyS_write+0xd4/0x1a0 fs/read_write.c:599
[<ffffffff83fc02c1>] entry_SYSCALL_64_fastpath+0x1f/0xc2
Code: 00 00 45 85 c9 75 46 e8 e9 65 29 fe 4c 8b 55 a8 49 bf 00 00 00
00 00 fc ff df 49 8d 7a 54 49 89 fb 48 89 f8 49 c1 eb 03 83 e0 07 <43>
0f b6 1c 3b 83 c0 01 38 d8 7c 08 84 db 0f 85 a9 03 00 00 48
RIP [< inline >] inet_exact_dif_match include/net/tcp.h:808
RIP [<ffffffff83091106>] __inet_lookup_listener+0xb6/0x500
net/ipv4/inet_hashtables.c:219
RSP <ffff88003b46f270>
---[ end trace 351d030d30a11e1a ]---
Kernel panic - not syncing: Fatal exception in interrupt
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled

On commit 0c183d92b20b5c84ca655b45ef57b3318b83eb9e (Oct 31).

Thanks!

[Eric Dumazet]

Thanks for your report.

David, please take a look.

TCP MD5 can call __inet_lookup_listener() with a NULL skb.

Bug added in commit a04a480d4392ea6efd117be2de564117b2a009c0

[David Ahern]

On 11/2/16 11:21 AM, Eric Dumazet wrote:
> Thanks for your report.
>
> David, please take a look.
>
> TCP MD5 can call __inet_lookup_listener() with a NULL skb.

interesting. I did not test md5 before sending, but doing so now I am not able to trigger the panic with any combination of passwords - correct, wrong, none, no listener, etc. perhaps I am missing a sysctl setting.

Will send a fix. I see the call to __inet_lookup_listener with null skb.

[Andrey Konovalov]

Hi David,

I'm able to reproduce it, so I'd be happy to test your fix.

Thanks!