BUG: KASAN: use-after-free in snd_timer_user_info_compat.isra.6+0x46c/0x480 sound/core/timer_compat.c:71
Read of size 8 at addr ffff8801d0dd9d00 by task syz-executor0/3342

CPU: 1 PID: 3342 Comm: syz-executor0 Not tainted 4.14.0-rc5+ #44
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:52
 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_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 snd_timer_user_info_compat.isra.6+0x46c/0x480 sound/core/timer_compat.c:71
 snd_timer_user_ioctl_compat+0x464/0x821 sound/core/timer_compat.c:160
 C_SYSC_ioctl fs/compat_ioctl.c:1593 [inline]
 compat_SyS_ioctl+0x1d7/0x3290 fs/compat_ioctl.c:1540
 do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline]
 do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391
 entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124
RIP: 0023:0xf7fd4c79
RSP: 002b:00000000f7faf05c EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000080e05411
RDX: 0000000020db8fe5 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 3341:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 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:3627
 kmalloc include/linux/slab.h:493 [inline]
 kzalloc include/linux/slab.h:666 [inline]
 snd_timer_instance_new+0xda/0x610 sound/core/timer.c:108
 snd_timer_open+0x180/0x1790 sound/core/timer.c:253
 snd_timer_user_tselect sound/core/timer.c:1655 [inline]
 __snd_timer_user_ioctl sound/core/timer.c:1918 [inline]
 snd_timer_user_ioctl+0x96f/0x32e0 sound/core/timer.c:1948
 snd_timer_user_ioctl_compat+0x615/0x821 sound/core/timer_compat.c:156
 C_SYSC_ioctl fs/compat_ioctl.c:1593 [inline]
 compat_SyS_ioctl+0x1d7/0x3290 fs/compat_ioctl.c:1540
 do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline]
 do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391
 entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124

Freed by task 3341:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 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:3503 [inline]
 kfree+0xca/0x250 mm/slab.c:3820
 snd_timer_close+0xa02/0xf20 sound/core/timer.c:374
 snd_timer_user_tselect sound/core/timer.c:1645 [inline]
 __snd_timer_user_ioctl sound/core/timer.c:1918 [inline]
 snd_timer_user_ioctl+0x80d/0x32e0 sound/core/timer.c:1948
 snd_timer_user_ioctl_compat+0x615/0x821 sound/core/timer_compat.c:156
 C_SYSC_ioctl fs/compat_ioctl.c:1593 [inline]
 compat_SyS_ioctl+0x1d7/0x3290 fs/compat_ioctl.c:1540
 do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline]
 do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391
 entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124

The buggy address belongs to the object at ffff8801d0dd9d00
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 0 bytes inside of
 256-byte region [ffff8801d0dd9d00, ffff8801d0dd9e00)
The buggy address belongs to the page:
page:ffffea0007437640 count:1 mapcount:0 mapping:ffff8801d0dd9080 index:0x0
flags: 0x200000000000100(slab)
raw: 0200000000000100 ffff8801d0dd9080 0000000000000000 000000010000000c
raw: ffffea000741b4a0 ffffea0007400820 ffff8801dac007c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d0dd9c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d0dd9c80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff8801d0dd9d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8801d0dd9d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d0dd9e00: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
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