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BUG: KASAN: use-after-free in relay_switch_subbuf+0x8c0/0x930 kernel/relay.c:755
Read of size 8 at addr ffff8880a0e63398 by task syz-executor.0/17471

CPU: 0 PID: 17471 Comm: syz-executor.0 Not tainted 5.1.0-rc3+ #57
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_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 relay_switch_subbuf+0x8c0/0x930 kernel/relay.c:755
 relay_flush kernel/relay.c:883 [inline]
 relay_flush+0x1c4/0x280 kernel/relay.c:867
 __blk_trace_startstop.isra.0+0x216/0x630 kernel/trace/blktrace.c:668
 blk_trace_ioctl+0x1c6/0x300 kernel/trace/blktrace.c:728
 blkdev_ioctl+0x276/0x1d10 block/ioctl.c:591
 block_ioctl+0xee/0x130 fs/block_dev.c:1933
 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: 0033:0x4582b9
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:00007f68ac32dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004582b9
RDX: 0000000020000080 RSI: 0000000000001275 RDI: 0000000000000003
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f68ac32e6d4
R13: 00000000004bf6c2 R14: 00000000004d1508 R15: 00000000ffffffff

Allocated by task 895:
 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_slab_alloc+0xf/0x20 mm/kasan/common.c:505
 slab_post_alloc_hook mm/slab.h:437 [inline]
 slab_alloc mm/slab.c:3394 [inline]
 kmem_cache_alloc+0x11a/0x6f0 mm/slab.c:3556
 __d_alloc+0x2e/0x8c0 fs/dcache.c:1622
 d_alloc+0x4d/0x2b0 fs/dcache.c:1701
 d_alloc_parallel+0xf4/0x1bc0 fs/dcache.c:2449
 __lookup_slow+0x1ab/0x500 fs/namei.c:1652
 lookup_one_len+0x16d/0x1a0 fs/namei.c:2541
 start_creating fs/debugfs/inode.c:313 [inline]
 start_creating+0xbf/0x1e0 fs/debugfs/inode.c:289
 __debugfs_create_file+0x65/0x400 fs/debugfs/inode.c:352
 debugfs_create_file+0x5a/0x70 fs/debugfs/inode.c:405
 blk_create_buf_file_callback+0x33/0x40 kernel/trace/blktrace.c:444
 relay_create_buf_file+0xfb/0x180 kernel/relay.c:428
 relay_open_buf.part.0+0x773/0xb60 kernel/relay.c:457
 relay_open_buf kernel/relay.c:449 [inline]
 relay_open kernel/relay.c:599 [inline]
 relay_open+0x523/0x980 kernel/relay.c:563
 do_blk_trace_setup+0x414/0xb90 kernel/trace/blktrace.c:532
 __blk_trace_setup+0xe3/0x190 kernel/trace/blktrace.c:577
 blk_trace_ioctl+0x170/0x300 kernel/trace/blktrace.c:716
 blkdev_ioctl+0x276/0x1d10 block/ioctl.c:591
 block_ioctl+0xee/0x130 fs/block_dev.c:1933
 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 820:
 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:3500 [inline]
 kmem_cache_free+0x86/0x260 mm/slab.c:3766
 __d_free+0x20/0x30 fs/dcache.c:269
 __rcu_reclaim kernel/rcu/rcu.h:227 [inline]
 rcu_do_batch kernel/rcu/tree.c:2475 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2788 [inline]
 rcu_core+0x928/0x1390 kernel/rcu/tree.c:2769
 __do_softirq+0x266/0x95a kernel/softirq.c:293

The buggy address belongs to the object at ffff8880a0e63340
 which belongs to the cache dentry(65:syz3) of size 288
The buggy address is located 88 bytes inside of
 288-byte region [ffff8880a0e63340, ffff8880a0e63460)
The buggy address belongs to the page:
page:ffffea00028398c0 count:1 mapcount:0 mapping:ffff88808c1fc980 index:0xffff8880a0e638c0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea00025ec988 ffffea000258f388 ffff88808c1fc980
raw: ffff8880a0e638c0 ffff8880a0e63080 0000000100000003 ffff88805e478040
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff88805e478040

Memory state around the buggy address:
 ffff8880a0e63280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a0e63300: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>ffff8880a0e63380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff8880a0e63400: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
 ffff8880a0e63480: fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb
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