net: llc: NULL ptr deref in llc_ui_sendmsg

Sasha Levin
2014-06-06T15:08:45Z

Hi all,

While fuzzing with trinity inside a KVM tools guest running the latest -next
kernel I've stumbled on the following spew:

[ 269.531162] BUG: unable to handle kernel NULL pointer dereference at 000000000000021e
[ 269.531217] IP: llc_ui_sendmsg (net/llc/af_llc.c:912)
[ 269.531232] PGD b6584067 PUD b6585067 PMD 0
[ 269.531246] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 269.531287] Dumping ftrace buffer:
[ 269.531451] (ftrace buffer empty)
[ 269.531472] Modules linked in:
[ 269.531483] CPU: 10 PID: 9450 Comm: trinity-c77 Not tainted 3.15.0-rc8-next-20140605-sasha-00021-ga95d8d2 #593
[ 269.531487] task: ffff8800b6563000 ti: ffff8800b659c000 task.ti: ffff8800b659c000
[ 269.531498] RIP: llc_ui_sendmsg (net/llc/af_llc.c:912)
[ 269.531501] RSP: 0018:ffff8800b659fcb8 EFLAGS: 00010286
[ 269.531505] RAX: 0000000000000000 RBX: ffff88006b5b8000 RCX: 0000000000000006
[ 269.531510] RDX: 0000000000007110 RSI: ffffffff9584f0f3 RDI: ffffffff957e75bd
[ 269.531515] RBP: ffff8800b659fd38 R08: 0000000000000000 R09: 0000000000000000
[ 269.531519] R10: 0000000000000001 R11: 0000000000000000 R12: ffff88006e177900
[ 269.531521] R13: ffff8800b659feb0 R14: 00000000007ffff7 R15: ffff8800b659fe78
[ 269.531524] FS: 00007f2b119bb700(0000) GS:ffff880292e00000(0000) knlGS:0000000000000000
[ 269.531528] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 269.531530] CR2: 000000000000021e CR3: 00000000b6583000 CR4: 00000000000006a0
[ 269.531610] DR0: 00000000006d6000 DR1: 0000000000000000 DR2: 0000000000000000
[ 269.531612] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000070602
[ 269.531616] Stack:
[ 269.531686] ffff8800b659fcc8 ffffffff911c488e ffff8800b659fce8 ffffffff00004002
[ 269.531695] 00000000b648d118 ffffffff912b923a ffff8800b659fd88 ffffffff911cb5be
[ 269.531709] ffff880000000000 ffffffff911a6ba8 000000000049c24f ffff8800b659fd48
[ 269.531712] Call Trace:
[ 269.531730] ? put_lock_stats.isra.12 (./arch/x86/include/asm/preempt.h:98 kernel/locking/lockdep.c:254)
[ 269.531746] ? might_fault (mm/memory.c:3735)
[ 269.531755] ? lock_release_non_nested (kernel/locking/lockdep.c:3397)
[ 269.531771] ? sched_clock_cpu (kernel/sched/clock.c:311)
[ 269.531779] sock_sendmsg (net/socket.c:654)
[ 269.531787] ? might_fault (mm/memory.c:3736)
[ 269.531793] ? might_fault (mm/memory.c:3735)
[ 269.531800] ? move_addr_to_kernel (./arch/x86/include/asm/uaccess.h:713 net/socket.c:197)
[ 269.531805] SYSC_sendto (net/socket.c:1812)
[ 269.531819] ? syscall_trace_enter (include/trace/events/syscalls.h:16 arch/x86/kernel/ptrace.c:1488)
[ 269.531827] SyS_sendto (net/socket.c:1779)
[ 269.531837] tracesys (arch/x86/kernel/entry_64.S:542)
[ 269.532403] Code: c6 c0 37 b2 98 4c 89 ef e8 95 a5 b6 fd 85 c0 74 d5 90 48 8b 83 f8 01 00 00 f6 c4 01 75 1c 48 8b 83 28 05 00 00 66 41 83 7d 04 00 <0f> b7 90 1e 02 00 00 75 1e eb 24 0f 1f 40 00 49 8b 7c 24 20 4c
All code
========
0: c6 c0 37 mov $0x37,%al
3: b2 98 mov $0x98,%dl
5: 4c 89 ef mov %r13,%rdi
8: e8 95 a5 b6 fd callq 0xfffffffffdb6a5a2
d: 85 c0 test %eax,%eax
f: 74 d5 je 0xffffffffffffffe6
11: 90 nop
12: 48 8b 83 f8 01 00 00 mov 0x1f8(%rbx),%rax
19: f6 c4 01 test $0x1,%ah
1c: 75 1c jne 0x3a
1e: 48 8b 83 28 05 00 00 mov 0x528(%rbx),%rax
25: 66 41 83 7d 04 00 cmpw $0x0,0x4(%r13)
2b:* 0f b7 90 1e 02 00 00 movzwl 0x21e(%rax),%edx <-- trapping instruction
32: 75 1e jne 0x52
34: eb 24 jmp 0x5a
36: 0f 1f 40 00 nopl 0x0(%rax)
3a: 49 8b 7c 24 20 mov 0x20(%r12),%rdi
3f: 4c rex.WR
...

Code starting with the faulting instruction
===========================================
0: 0f b7 90 1e 02 00 00 movzwl 0x21e(%rax),%edx
7: 75 1e jne 0x27
9: eb 24 jmp 0x2f
b: 0f 1f 40 00 nopl 0x0(%rax)
f: 49 8b 7c 24 20 mov 0x20(%r12),%rdi
14: 4c rex.WR
...
[ 269.532565] RIP llc_ui_sendmsg (net/llc/af_llc.c:912)
[ 269.532572] RSP <ffff8800b659fcb8>
[ 269.532575] CR2: 000000000000021e

Thanks,
Sasha