Hello,

syzbot found the following crash on:

HEAD commit: bf3bd966 Merge tag 'usb-5.1-rc8' of git://git.kernel.org/p.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=1431a0e0a00000 kernel config: https://syzkaller.appspot.com/x/.config?x=ef1b87b455c397cf dashboard link: https://syzkaller.appspot.com/bug?extid=20ab495fadf081e8a2b0 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+20ab495fadf081e8a2b0@syzkaller.appspotmail.com

================================================================== BUG: KASAN: use-after-free in __list_add include/linux/list.h:64 [inline] BUG: KASAN: use-after-free in list_add_tail include/linux/list.h:93 [inline] BUG: KASAN: use-after-free in check_and_subscribe_port+0x7bd/0x860 sound/core/seq/seq_ports.c:524 Write of size 8 at addr ffff88809587bba0 by task syz-executor.2/19168

CPU: 0 PID: 19168 Comm: syz-executor.2 Not tainted 5.1.0-rc7+ #95 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+0x172/0x1f0 lib/dump_stack.c:113 print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187 kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317 __asan_report_store8_noabort+0x17/0x20 mm/kasan/generic_report.c:137 __list_add include/linux/list.h:64 [inline] list_add_tail include/linux/list.h:93 [inline] check_and_subscribe_port+0x7bd/0x860 sound/core/seq/seq_ports.c:524 snd_seq_port_connect+0x388/0x510 sound/core/seq/seq_ports.c:587 snd_seq_ioctl_subscribe_port+0x1e5/0x310 sound/core/seq/seq_clientmgr.c:1458 snd_seq_ioctl+0x224/0x3e0 sound/core/seq/seq_clientmgr.c:2138 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:509 [inline] do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713 __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x458da9 Code: ad b8 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 b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f6a5c605c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458da9 RDX: 0000000020000000 RSI: 0000000040505330 RDI: 0000000000000003 RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6a5c6066d4 R13: 00000000004cc598 R14: 00000000004d5ee8 R15: 00000000ffffffff

Allocated by task 19168: save_stack+0x45/0xd0 mm/kasan/common.c:75 set_track mm/kasan/common.c:87 [inline] __kasan_kmalloc mm/kasan/common.c:497 [inline] __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:470 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:511 kmem_cache_alloc_trace+0x151/0x760 mm/slab.c:3622 kmalloc include/linux/slab.h:547 [inline] kzalloc include/linux/slab.h:742 [inline] snd_seq_port_connect+0x60/0x510 sound/core/seq/seq_ports.c:571 snd_seq_ioctl_subscribe_port+0x1e5/0x310 sound/core/seq/seq_clientmgr.c:1458 snd_seq_ioctl+0x224/0x3e0 sound/core/seq/seq_clientmgr.c:2138 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:509 [inline] do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713 __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 19167: save_stack+0x45/0xd0 mm/kasan/common.c:75 set_track mm/kasan/common.c:87 [inline] __kasan_slab_free+0x102/0x150 mm/kasan/common.c:459 kasan_slab_free+0xe/0x10 mm/kasan/common.c:467 __cache_free mm/slab.c:3499 [inline] kfree+0xcf/0x230 mm/slab.c:3822 snd_seq_port_disconnect+0x209/0x280 sound/core/seq/seq_ports.c:632 snd_seq_ioctl_unsubscribe_port+0x1e5/0x310 sound/core/seq/seq_clientmgr.c:1499 snd_seq_ioctl+0x224/0x3e0 sound/core/seq/seq_clientmgr.c:2138 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:509 [inline] do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713 __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88809587bb40 which belongs to the cache kmalloc-128 of size 128 The buggy address is located 96 bytes inside of 128-byte region [ffff88809587bb40, ffff88809587bbc0) The buggy address belongs to the page: page:ffffea0002561ec0 count:1 mapcount:0 mapping:ffff8880aa400640 index:0xffff88809587bd80 flags: 0x1fffc0000000200(slab) raw: 01fffc0000000200 ffffea0002949788 ffffea0002906888 ffff8880aa400640 raw: ffff88809587bd80 ffff88809587b000 000000010000000f 0000000000000000 page dumped because: kasan: bad access detected

Memory state around the buggy address: ffff88809587ba80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88809587bb00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb

ffff88809587bb80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc

^ ffff88809587bc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88809587bc80: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00 ==================================================================

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