RE: KASAN: use-after-free Read in tipc_group_size

-----Original Message-----
From: Cong Wang [mailto:xiyou.wangcong@gmail.com]
Sent: Monday, January 08, 2018 13:44
To: syzbot <redacted>
Cc: David Miller <davem@davemloft.net>; Jon Maloy
[off-list ref]; LKML [off-list ref]; Linux
Kernel Network Developers [off-list ref]; syzkaller-
bugs@googlegroups.com; tipc-discussion@lists.sourceforge.net; Ying Xue
[off-list ref]
Subject: Re: KASAN: use-after-free Read in tipc_group_size

On Mon, Jan 8, 2018 at 6:58 AM, syzbot
[off-list ref] wrote:

quoted

Hello,

syzkaller hit the following crash on
b2cd1df66037e7c4697c7e40496bf7e4a5e16a2d
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/maste
r
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ for
information about syzkaller reproducers


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Reported-by: syzbot+aae58876fb5a1fad0a4b@syzkaller.appspotmail.com
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==========================================================
========

quoted

BUG: KASAN: use-after-free in tipc_group_size+0x40/0x50
net/tipc/group.c:158 Read of size 2 at addr ffff8801c08ba280 by task
syzkaller447710/3513

CPU: 0 PID: 3513 Comm: syzkaller447710 Not tainted 4.15.0-rc7+ #252
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011 Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:428
 tipc_group_size+0x40/0x50 net/tipc/group.c:158
 tipc_poll+0x374/0x4f0 net/tipc/socket.c:739

Seems we have to lock the sock for tipc_group_size() in tipc_poll().

Not quite. I think it is that we initialize 'grp' on the stack before we call sock_poll_wait() and access it after it returns.
This is anyway fixed in patch #9 of the series I just sent to net-next, where the poll() handling for group members is redesigned.

///jon

quoted

 sock_poll+0x141/0x320 net/socket.c:1117  do_pollfd fs/select.c:822
[inline]  do_poll fs/select.c:872 [inline]
 do_sys_poll+0x715/0x10b0 fs/select.c:966  SYSC_poll fs/select.c:1024
[inline]
 SyS_poll+0x10d/0x450 fs/select.c:1012
entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x445cb9
RSP: 002b:00007f04886b1ce8 EFLAGS: 00000246 ORIG_RAX:

0000000000000007

quoted

RAX: ffffffffffffffda RBX: 00000000006dac3c RCX: 0000000000445cb9
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000020fa2ff8
RBP: 00000000006dac38 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffc84d56d7f R14: 00007f04886b29c0 R15: 0000000000000005

Allocated by task 3510:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447  set_track
mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3610  kmalloc
include/linux/slab.h:499 [inline]  kzalloc include/linux/slab.h:688
[inline]
 tipc_group_create+0x116/0x9c0 net/tipc/group.c:167  tipc_sk_join
net/tipc/socket.c:2747 [inline]
 tipc_setsockopt+0x249/0xc10 net/tipc/socket.c:2861  SYSC_setsockopt
net/socket.c:1829 [inline]
 SyS_setsockopt+0x189/0x360 net/socket.c:1808
entry_SYSCALL_64_fastpath+0x23/0x9a

Freed by task 3510:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447  set_track
mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524  __cache_free
mm/slab.c:3488 [inline]
 kfree+0xd6/0x260 mm/slab.c:3803
 tipc_group_delete+0x2c8/0x3d0 net/tipc/group.c:206  tipc_sk_join
net/tipc/socket.c:2760 [inline]
 tipc_setsockopt+0xb0d/0xc10 net/tipc/socket.c:2861  SYSC_setsockopt
net/socket.c:1829 [inline]
 SyS_setsockopt+0x189/0x360 net/socket.c:1808
entry_SYSCALL_64_fastpath+0x23/0x9a

The buggy address belongs to the object at ffff8801c08ba200  which
belongs to the cache kmalloc-192 of size 192 The buggy address is
located 128 bytes inside of  192-byte region [ffff8801c08ba200,
ffff8801c08ba2c0) The buggy address belongs to the page:
page:ffffea0007022e80 count:1 mapcount:0 mapping:ffff8801c08ba000
index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c08ba000 0000000000000000
0000000100000010
raw: ffffea00071338a0 ffffea0006fe2360 ffff8801dac00040
0000000000000000 page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c08ba180: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff8801c08ba200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

quoted

ffff8801c08ba280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc

                   ^
 ffff8801c08ba300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c08ba380: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc

==========================================================
========

quoted

---
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