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SubjectKASAN: use-after-free Read in snd_timer_resolution
From
Hello,

syzbot found the following crash on:

HEAD commit: e033e7d4 Merge branch 'dhowells' (patches from DavidH)
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12f2bb25e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=d9290aeb7e6cf1c4
dashboard link: https://syzkaller.appspot.com/bug?extid=2b2ef983f973e5c40943
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2b2ef983f973e5c40943@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in snd_timer_resolution+0xf1/0x110
sound/core/timer.c:441
Read of size 8 at addr ffff888094155800 by task syz-executor.0/18632

CPU: 1 PID: 18632 Comm: syz-executor.0 Not tainted 5.5.0-rc6-syzkaller #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:639
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
snd_timer_resolution+0xf1/0x110 sound/core/timer.c:441
snd_seq_info_timer_read+0x95/0x2f1 sound/core/seq/seq_timer.c:480
snd_info_seq_show+0xcb/0x120 sound/core/info.c:363
seq_read+0x4ca/0x1170 fs/seq_file.c:229
proc_reg_read+0x1fc/0x2c0 fs/proc/inode.c:223
do_loop_readv_writev fs/read_write.c:714 [inline]
do_loop_readv_writev fs/read_write.c:701 [inline]
do_iter_read+0x4a4/0x660 fs/read_write.c:935
compat_readv+0x187/0x1f0 fs/read_write.c:1186
do_compat_preadv64+0x190/0x1c0 fs/read_write.c:1235
__do_compat_sys_preadv fs/read_write.c:1255 [inline]
__se_compat_sys_preadv fs/read_write.c:1249 [inline]
__ia32_compat_sys_preadv+0xc7/0x140 fs/read_write.c:1249
do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline]
do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f6da39
Code: 00 00 00 89 d3 5b 5e 5f 5d c3 b8 80 96 98 00 eb c4 8b 04 24 c3 8b 1c
24 c3 8b 34 24 c3 8b 3c 24 c3 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90
90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f5d690cc EFLAGS: 00000296 ORIG_RAX: 000000000000014d
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00000000200017c0
RDX: 00000000000003da RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 18631:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
__kasan_kmalloc mm/kasan/common.c:513 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
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_seq_timer_open+0x1c0/0x590 sound/core/seq/seq_timer.c:275
queue_use+0xf1/0x270 sound/core/seq/seq_queue.c:489
snd_seq_queue_alloc+0x2c5/0x4d0 sound/core/seq/seq_queue.c:176
snd_seq_ioctl_create_queue+0xb0/0x330 sound/core/seq/seq_clientmgr.c:1548
snd_seq_kernel_client_ctl+0xf8/0x140 sound/core/seq/seq_clientmgr.c:2353
alloc_seq_queue.isra.0+0xdc/0x180 sound/core/seq/oss/seq_oss_init.c:357
snd_seq_oss_open+0x2ff/0x960 sound/core/seq/oss/seq_oss_init.c:215
odev_open+0x70/0x90 sound/core/seq/oss/seq_oss.c:125
soundcore_open+0x453/0x610 sound/sound_core.c:593
chrdev_open+0x245/0x6b0 fs/char_dev.c:414
do_dentry_open+0x4e6/0x1380 fs/open.c:797
vfs_open+0xa0/0xd0 fs/open.c:914
do_last fs/namei.c:3420 [inline]
path_openat+0x10df/0x4500 fs/namei.c:3537
do_filp_open+0x1a1/0x280 fs/namei.c:3567
do_sys_open+0x3fe/0x5d0 fs/open.c:1097
__do_compat_sys_openat fs/open.c:1143 [inline]
__se_compat_sys_openat fs/open.c:1141 [inline]
__ia32_compat_sys_openat+0x98/0xf0 fs/open.c:1141
do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline]
do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

Freed by task 18630:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
kasan_set_free_info mm/kasan/common.c:335 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
__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_seq_timer_close+0x99/0xe0 sound/core/seq/seq_timer.c:319
queue_delete+0x52/0xb0 sound/core/seq/seq_queue.c:134
snd_seq_queue_delete+0x4e/0x70 sound/core/seq/seq_queue.c:196
snd_seq_ioctl_delete_queue+0x6a/0x90 sound/core/seq/seq_clientmgr.c:1570
snd_seq_kernel_client_ctl+0xf8/0x140 sound/core/seq/seq_clientmgr.c:2353
delete_seq_queue.part.0+0xb6/0x120 sound/core/seq/oss/seq_oss_init.c:376
delete_seq_queue sound/core/seq/oss/seq_oss_init.c:372 [inline]
snd_seq_oss_release+0x116/0x150 sound/core/seq/oss/seq_oss_init.c:421
odev_release+0x54/0x80 sound/core/seq/oss/seq_oss.c:140
__fput+0x2ff/0x890 fs/file_table.c:280
____fput+0x16/0x20 fs/file_table.c:313
task_work_run+0x145/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
do_syscall_32_irqs_on arch/x86/entry/common.c:352 [inline]
do_fast_syscall_32+0xbbd/0xe16 arch/x86/entry/common.c:408
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

The buggy address belongs to the object at ffff888094155800
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 0 bytes inside of
256-byte region [ffff888094155800, ffff888094155900)
The buggy address belongs to the page:
page:ffffea0002505540 refcount:1 mapcount:0 mapping:ffff8880aa4008c0
index:0x0
raw: 00fffe0000000200 ffffea00024df348 ffffea00024af508 ffff8880aa4008c0
raw: 0000000000000000 ffff888094155000 0000000100000008 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888094155700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888094155780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff888094155800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888094155880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888094155900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

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