Hello,

syzbot found the following crash on:

HEAD commit: d1abaeb3 Linux 5.3-rc5 git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=15b5add2600000 kernel config: https://syzkaller.appspot.com/x/.config?x=f7242b2607d5d53a dashboard link: https://syzkaller.appspot.com/bug?extid=4a75454b9ca2777f35c7 compiler: clang version 9.0.0 (/home/glider/llvm/clang 80fee25776c2fb61e74c1ecb1a523375c2500b69)

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+4a75454b9ca2777f35c7@syzkaller.appspotmail.com

================================================================== BUG: KASAN: use-after-free in atomic_read include/asm-generic/atomic-instrumented.h:26 [inline] BUG: KASAN: use-after-free in snd_seq_unused_cells sound/core/seq/seq_memory.h:60 [inline] BUG: KASAN: use-after-free in snd_seq_ioctl_get_client_pool+0x2e0/0x680 sound/core/seq/seq_clientmgr.c:1839 Read of size 4 at addr ffff8880a8e27b14 by task syz-executor.5/31741

CPU: 0 PID: 31741 Comm: syz-executor.5 Not tainted 5.3.0-rc5 #82 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+0x1d8/0x2f8 lib/dump_stack.c:113 print_address_description+0x75/0x5b0 mm/kasan/report.c:351 __kasan_report+0x14b/0x1c0 mm/kasan/report.c:482 kasan_report+0x26/0x50 mm/kasan/common.c:612 check_memory_region_inline mm/kasan/generic.c:182 [inline] check_memory_region+0x2cf/0x2e0 mm/kasan/generic.c:192 __kasan_check_read+0x11/0x20 mm/kasan/common.c:92 atomic_read include/asm-generic/atomic-instrumented.h:26 [inline] snd_seq_unused_cells sound/core/seq/seq_memory.h:60 [inline] snd_seq_ioctl_get_client_pool+0x2e0/0x680 sound/core/seq/seq_clientmgr.c:1839 snd_seq_ioctl+0x1d1/0x340 sound/core/seq/seq_clientmgr.c:2158 do_vfs_ioctl+0x744/0x1730 fs/ioctl.c:46 ksys_ioctl fs/ioctl.c:713 [inline] __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0xe3/0x120 fs/ioctl.c:718 do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:296 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x459829 Code: fd b7 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 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007faf5e0c4c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459829 RDX: 00000000200003c0 RSI: 00000000c058534b RDI: 0000000000000003 RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007faf5e0c56d4 R13: 00000000004cdc18 R14: 00000000004d7ba8 R15: 00000000ffffffff

Allocated by task 31737: save_stack mm/kasan/common.c:69 [inline] set_track mm/kasan/common.c:77 [inline] __kasan_kmalloc+0x11c/0x1b0 mm/kasan/common.c:487 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:501 kmem_cache_alloc_trace+0x221/0x2f0 mm/slab.c:3550 kmalloc include/linux/slab.h:552 [inline] kzalloc include/linux/slab.h:748 [inline] snd_seq_pool_new+0x53/0x1b0 sound/core/seq/seq_memory.c:459 snd_seq_fifo_new+0x72/0x1c0 sound/core/seq/seq_fifo.c:26 snd_seq_open+0x1e4/0x470 sound/core/seq/seq_clientmgr.c:350 snd_open+0x313/0x380 sound/core/sound.c:163 chrdev_open+0x509/0x590 fs/char_dev.c:414 do_dentry_open+0x73b/0xf90 fs/open.c:797 vfs_open+0x73/0x80 fs/open.c:906 do_last fs/namei.c:3416 [inline] path_openat+0x1397/0x4460 fs/namei.c:3533 do_filp_open+0x192/0x3d0 fs/namei.c:3563 do_sys_open+0x29f/0x560 fs/open.c:1089 __do_sys_open fs/open.c:1107 [inline] __se_sys_open fs/open.c:1102 [inline] __x64_sys_open+0x87/0x90 fs/open.c:1102 do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:296 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 31737: save_stack mm/kasan/common.c:69 [inline] set_track mm/kasan/common.c:77 [inline] __kasan_slab_free+0x12a/0x1e0 mm/kasan/common.c:449 kasan_slab_free+0xe/0x10 mm/kasan/common.c:457 __cache_free mm/slab.c:3425 [inline] kfree+0x115/0x200 mm/slab.c:3756 snd_seq_pool_delete+0x9e/0xd0 sound/core/seq/seq_memory.c:487 snd_seq_fifo_resize+0x1de/0x250 sound/core/seq/seq_fifo.c:262 snd_seq_ioctl_set_client_pool+0x3c4/0x740 sound/core/seq/seq_clientmgr.c:1880 snd_seq_ioctl+0x1d1/0x340 sound/core/seq/seq_clientmgr.c:2158 do_vfs_ioctl+0x744/0x1730 fs/ioctl.c:46 ksys_ioctl fs/ioctl.c:713 [inline] __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0xe3/0x120 fs/ioctl.c:718 do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:296 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a8e27b00 which belongs to the cache kmalloc-192 of size 192 The buggy address is located 20 bytes inside of 192-byte region [ffff8880a8e27b00, ffff8880a8e27bc0) The buggy address belongs to the page: page:ffffea0002a389c0 refcount:1 mapcount:0 mapping:ffff8880aa400000 index:0x0 flags: 0x1fffc0000000200(slab) raw: 01fffc0000000200 ffffea00026d1008 ffffea0002870048 ffff8880aa400000 raw: 0000000000000000 ffff8880a8e27000 0000000100000010 0000000000000000 page dumped because: kasan: bad access detected

Memory state around the buggy address: ffff8880a8e27a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880a8e27a80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc

ffff8880a8e27b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

^ ffff8880a8e27b80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff8880a8e27c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================

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