net/ipv6: null-ptr-deref in inet6_bind

[Andrey Konovalov]

Hi,

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

BUG: unable to handle kernel NULL pointer dereference at           (null)
IP: [<          (null)>]           (null)
PGD 66b6f067 [  102.549865] PUD 66c6e067
PMD 0 [  102.549865]
Oops: 0010 [#1] SMP KASAN
Modules linked in:
CPU: 0 PID: 4143 Comm: a.out Not tainted 4.9.0-rc3+ #336
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff880066b1c200 task.stack: ffff880065b58000
RIP: 0010:[<0000000000000000>]  [<          (null)>]           (null)
RSP: 0018:ffff880065b5fbc0  EFLAGS: 00010246
RAX: ffff880066b1c200 RBX: ffff88006873864a RCX: 0000000000000000
RDX: 0000000000000001 RSI: ffff880068738640 RDI: ffff880063bd3200
RBP: ffff880065b5fd20 R08: 1ffff1000c77a713 R09: dffffc0000000000
R10: ffffffff844fc800 R11: 1ffff1000d0e70c9 R12: ffffffff84e7e040
R13: ffff880068738640 R14: ffff880063bd3200 R15: ffffffff86836380
FS:  00007f40b7acf700(0000) GS:ffff88006cc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000006bb28000 CR4: 00000000000006f0
Stack:
 ffffffff83099988 ffffffff8479f7e8 ffffffff81208580 1ffff1000000000c
 0000000041b58ab3 ffffffff8479f7e8 ffffffff81208580 ffffffff812506ed
 0000000000000007 ffff880065b5fc18 ffffffff812506ed ffff880065b5fcd0
Call Trace:
 [<ffffffff832cf4fc>] inet6_bind+0x8ec/0x1020 net/ipv6/af_inet6.c:384
 [<ffffffff82b7033c>] SYSC_bind+0x1ec/0x250 net/socket.c:1367
 [<ffffffff82b72ae4>] SyS_bind+0x24/0x30 net/socket.c:1353
 [<ffffffff83fc0401>] entry_SYSCALL_64_fastpath+0x1f/0xc2
arch/x86/entry/entry_64.S:209
Code:  Bad RIP value.
RIP  [<          (null)>]           (null)
 RSP <ffff880065b5fbc0>
CR2: 0000000000000000
---[ end trace b5ec698ae4926a97 ]---
Kernel panic - not syncing: Fatal exception in interrupt
Kernel Offset: disabled
---[ end Kernel panic - not syncing: Fatal exception in interrupt

On commit 0c183d92b20b5c84ca655b45ef57b3318b83eb9e (Oct 31).

I'm able to reproduce it with the attached program by running it as:
$ gcc -lpthread inet6-bind-poc.c
$ while true; do ./a.out; done

Thanks!

Attachment: inet6-bind-poc.c
Description: Binary data