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=1658f9fce00000 kernel config: https://syzkaller.appspot.com/x/.config?x=2af7db1972ec750e dashboard link: https://syzkaller.appspot.com/bug?extid=5ab7470f121c0165470f compiler: gcc (GCC) 9.0.0 20181231 (experimental)

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+5ab7470f121c0165470f@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 ffff888095ac8078 by task syz-executor.0/4457

CPU: 1 PID: 4457 Comm: syz-executor.0 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] list_move_tail include/linux/list.h:214 [inline] check_matching_master_slave.part.0+0x116/0x550 sound/core/timer.c:179 check_matching_master_slave sound/core/timer.c:177 [inline] snd_timer_check_slave sound/core/timer.c:207 [inline] snd_timer_open+0x466/0x1150 sound/core/timer.c:270 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: 0033:0x45a219 Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f41e77d2c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a219 RDX: 0000000020029fcc RSI: 0000000040345410 RDI: 0000000000000003 RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f41e77d36d4 R13: 00000000004cf428 R14: 00000000004d9760 R15: 00000000ffffffff

Allocated by task 4339: 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 4339: 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 ffff888095ac8000 which belongs to the cache kmalloc-256 of size 256 The buggy address is located 120 bytes inside of 256-byte region [ffff888095ac8000, ffff888095ac8100) The buggy address belongs to the page: page:ffffea000256b200 refcount:1 mapcount:0 mapping:ffff8880aa4008c0 index:0xffff888095ac8c00 flags: 0x1fffc0000000200(slab) raw: 01fffc0000000200 ffffea0001815608 ffffea0001eb9308 ffff8880aa4008c0 raw: ffff888095ac8c00 ffff888095ac8000 0000000100000005 0000000000000000 page dumped because: kasan: bad access detected

Memory state around the buggy address: ffff888095ac7f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff888095ac7f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

ffff888095ac8000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

^ ffff888095ac8080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888095ac8100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ==================================================================

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