Re: KASAN: slab-out-of-bounds Read in rds_cong_queue_updates

On Thu, Feb 22, 2018 at 12:49 PM, syzbot
[off-list ref] wrote:

Hello,

syzbot hit the following crash on upstream commit
79c0ef3e85c015b0921a8fd5dd539d1480e9cd6c (Mon Feb 19 19:58:19 2018 +0000)
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

So far this crash happened 28 times on
https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/master.
Unfortunately, I don't have any reproducer for this crash yet.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.
user-space arch: i386

This looks the same as:

#syz dup: KASAN: use-after-free Read in rds_cong_queue_updates

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==================================================================
BUG: KASAN: slab-out-of-bounds in __read_once_size
include/linux/compiler.h:183 [inline]
BUG: KASAN: slab-out-of-bounds in atomic_read
arch/x86/include/asm/atomic.h:27 [inline]
BUG: KASAN: slab-out-of-bounds in refcount_read include/linux/refcount.h:42
[inline]
BUG: KASAN: slab-out-of-bounds in check_net include/net/net_namespace.h:228
[inline]
BUG: KASAN: slab-out-of-bounds in rds_destroy_pending net/rds/rds.h:868
[inline]
BUG: KASAN: slab-out-of-bounds in rds_cong_queue_updates+0x4d2/0x4f0
net/rds/cong.c:226
Read of size 4 at addr ffff8801d31a0044 by task syz-executor1/21851

CPU: 1 PID: 21851 Comm: syz-executor1 Not tainted 4.16.0-rc2+ #232
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:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23b/0x360 mm/kasan/report.c:412
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
 __read_once_size include/linux/compiler.h:183 [inline]
 atomic_read arch/x86/include/asm/atomic.h:27 [inline]
 refcount_read include/linux/refcount.h:42 [inline]
 check_net include/net/net_namespace.h:228 [inline]
 rds_destroy_pending net/rds/rds.h:868 [inline]
 rds_cong_queue_updates+0x4d2/0x4f0 net/rds/cong.c:226
 rds_recv_rcvbuf_delta.part.2+0x289/0x320 net/rds/recv.c:118
 rds_recv_rcvbuf_delta net/rds/recv.c:377 [inline]
 rds_recv_incoming+0xeb4/0x11d0 net/rds/recv.c:377
 rds_loop_xmit+0x149/0x320 net/rds/loop.c:82
 rds_send_xmit+0xbcc/0x26b0 net/rds/send.c:355
 rds_sendmsg+0x1fcb/0x2390 net/rds/send.c:1208
 sock_sendmsg_nosec net/socket.c:630 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:640
 SYSC_sendto+0x361/0x5c0 net/socket.c:1747
 SyS_sendto+0x40/0x50 net/socket.c:1715
 do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f9ac79
RSP: 002b:00000000f779609c EFLAGS: 00000286 ORIG_RAX: 0000000000000171
RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 0000000020f7db7f
RDX: 0000000000000481 RSI: 0000000000000000 RDI: 000000002069affb
RBP: 0000000000000010 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 20583:
 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:552
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3541
 getname_flags+0xcb/0x580 fs/namei.c:138
 user_path_at_empty+0x2d/0x50 fs/namei.c:2568
 user_path_at include/linux/namei.h:57 [inline]
 SYSC_chdir fs/open.c:440 [inline]
 SyS_chdir+0xb0/0x200 fs/open.c:434
 do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

Freed by task 20583:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
 __cache_free mm/slab.c:3485 [inline]
 kmem_cache_free+0x83/0x2a0 mm/slab.c:3743
 putname+0xee/0x130 fs/namei.c:258
 filename_lookup+0x315/0x500 fs/namei.c:2323
 user_path_at_empty+0x40/0x50 fs/namei.c:2568
 user_path_at include/linux/namei.h:57 [inline]
 SYSC_chdir fs/open.c:440 [inline]
 SyS_chdir+0xb0/0x200 fs/open.c:434
 do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

The buggy address belongs to the object at ffff8801d31a0a00
 which belongs to the cache names_cache of size 4096
The buggy address is located 2492 bytes to the left of
 4096-byte region [ffff8801d31a0a00, ffff8801d31a1a00)
The buggy address belongs to the page:
page:ffffea00074c6800 count:1 mapcount:0 mapping:ffff8801d31a0a00 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801d31a0a00 0000000000000000 0000000100000001
raw: ffffea0006d3b820 ffffea0006cf3920 ffff8801da9d4600 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d319ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801d319ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

quoted

ffff8801d31a0000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

                                           ^
 ffff8801d31a0080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801d31a0100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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On (03/19/18 09:29), Dmitry Vyukov wrote:

This looks the same as:

#syz dup: KASAN: use-after-free Read in rds_cong_queue_updates

correct, seems like the rds_destroy_pending() fixes did not seal
this race condition. I need to look at this more carefully to see
what race I missed.. no easy answer here, I am afraid.

--Sowmini

On Mon, Mar 19, 2018 at 9:37 AM, Sowmini Varadhan
[off-list ref] wrote:

On (03/19/18 09:29), Dmitry Vyukov wrote:

quoted

This looks the same as:

#syz dup: KASAN: use-after-free Read in rds_cong_queue_updates

correct, seems like the rds_destroy_pending() fixes did not seal
this race condition. I need to look at this more carefully to see
what race I missed.. no easy answer here, I am afraid.

Hi Sowmini,

What fix do you mean? syzbot does not know about any fixes for any of
the bugs as far as I see. So maybe your fix actually fixed it, but
it's not in upstream yes, and syzbot still finds this in upstream.
We tell syzbot about fixes (with Reported-by tags or "#syz fix" email
commands) to be able to later make sense of the state of the bugs.