KASAN: use-after-free Read in snd_timer_open

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 6980b7f6 Add linux-next specific files for 20191111
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=101679e6e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=2af7db1972ec750e
dashboard link: https://syzkaller.appspot.com/bug?extid=4476917c053f60112c99
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=108fbfece00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1055d5aae00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+447691...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in __list_add_valid+0x9a/0xa0 lib/list_debug.c:26
Read of size 8 at addr ffff88809fccee78 by task syz-executor075/8825

CPU: 0 PID: 8825 Comm: syz-executor075 Not tainted 5.4.0-rc6-next-20191111
#0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:634
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
__list_add_valid+0x9a/0xa0 lib/list_debug.c:26
__list_add include/linux/list.h:60 [inline]
list_add_tail include/linux/list.h:93 [inline]
snd_timer_open+0x245/0x1150 sound/core/timer.c:268
snd_timer_user_tselect sound/core/timer.c:1738 [inline]
__snd_timer_user_ioctl.isra.0+0x7ed/0x2070 sound/core/timer.c:2008
snd_timer_user_ioctl+0x7a/0xa7 sound/core/timer.c:2038
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:545 [inline]
do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
__do_sys_ioctl fs/ioctl.c:756 [inline]
__se_sys_ioctl fs/ioctl.c:754 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x444f39
Code: e8 fc ab 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 bb cd fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffd1d1e3c98 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000444f39
RDX: 0000000020029fcc RSI: 0000000040345410 RDI: 0000000000000003
RBP: 00000000000102a7 R08: 0000000000000004 R09: 00000000004002e0
R10: 000000000000000f R11: 0000000000000246 R12: 0000000000402180
R13: 0000000000402210 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 8824:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
__kasan_kmalloc mm/kasan/common.c:510 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:483
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:524
kmem_cache_alloc_trace+0x158/0x790 mm/slab.c:3551
kmalloc include/linux/slab.h:556 [inline]
kzalloc include/linux/slab.h:670 [inline]
snd_timer_instance_new+0x4a/0x300 sound/core/timer.c:96
snd_timer_user_tselect sound/core/timer.c:1725 [inline]
__snd_timer_user_ioctl.isra.0+0x665/0x2070 sound/core/timer.c:2008
snd_timer_user_ioctl+0x7a/0xa7 sound/core/timer.c:2038
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:545 [inline]
do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
__do_sys_ioctl fs/ioctl.c:756 [inline]
__se_sys_ioctl fs/ioctl.c:754 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8824:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
kasan_set_free_info mm/kasan/common.c:332 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:471
kasan_slab_free+0xe/0x10 mm/kasan/common.c:480
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3757
snd_timer_instance_free sound/core/timer.c:120 [inline]
snd_timer_instance_free+0x7c/0xa0 sound/core/timer.c:114
snd_timer_user_tselect sound/core/timer.c:1740 [inline]
__snd_timer_user_ioctl.isra.0+0x160d/0x2070 sound/core/timer.c:2008
snd_timer_user_ioctl+0x7a/0xa7 sound/core/timer.c:2038
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:545 [inline]
do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
__do_sys_ioctl fs/ioctl.c:756 [inline]
__se_sys_ioctl fs/ioctl.c:754 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88809fccee00
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 120 bytes inside of
256-byte region [ffff88809fccee00, ffff88809fccef00)
The buggy address belongs to the page:
page:ffffea00027f3380 refcount:1 mapcount:0 mapping:ffff8880aa4008c0
index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea00027f2e08 ffff8880aa401648 ffff8880aa4008c0
raw: 0000000000000000 ffff88809fcce000 0000000100000008 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809fcced00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88809fcced80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff88809fccee00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88809fccee80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809fccef00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
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[syzbot]

syzbot has bisected this bug to:

commit 6a34367e52caea1413eb0a0dcbb524f0c9b67e82
Author: Takashi Iwai <ti...@suse.de>
Date: Thu Nov 7 19:20:08 2019 +0000

ALSA: timer: Fix possible race at assigning a timer instance

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16b5dde6e00000
start commit: 6980b7f6 Add linux-next specific files for 20191111
git tree: linux-next
final crash: https://syzkaller.appspot.com/x/report.txt?x=15b5dde6e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=11b5dde6e00000

kernel config: https://syzkaller.appspot.com/x/.config?x=2af7db1972ec750e
dashboard link: https://syzkaller.appspot.com/bug?extid=4476917c053f60112c99

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=108fbfece00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1055d5aae00000

Reported-by: syzbot+447691...@syzkaller.appspotmail.com
Fixes: 6a34367e52ca ("ALSA: timer: Fix possible race at assigning a timer
instance")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection