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BUG: KASAN: use-after-free in relay_switch_subbuf+0x8be/0x920 kernel/relay.c:755
Read of size 8 at addr ffff88803e9201b8 by task syz-executor.5/11782

CPU: 0 PID: 11782 Comm: syz-executor.5 Not tainted 5.3.0-rc8+ #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+0x172/0x1f0 lib/dump_stack.c:113
 print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
 __kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
 kasan_report+0x12/0x17 mm/kasan/common.c:618
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 relay_switch_subbuf+0x8be/0x920 kernel/relay.c:755
 relay_reserve include/linux/relay.h:261 [inline]
 trace_note.isra.0+0x5b8/0x6e0 kernel/trace/blktrace.c:93
 trace_note_tsk kernel/trace/blktrace.c:124 [inline]
 __blk_add_trace+0xb70/0xe10 kernel/trace/blktrace.c:264
 blk_add_trace_bio.isra.0+0x19c/0x220 kernel/trace/blktrace.c:865
 blk_add_trace_bio_queue+0x46/0x60 kernel/trace/blktrace.c:902
 trace_block_bio_queue include/trace/events/block.h:357 [inline]
 generic_make_request_checks+0x16c3/0x21a0 block/blk-core.c:954
 generic_make_request+0x8f/0xb50 block/blk-core.c:1006
 submit_bio+0x104/0x4d0 block/blk-core.c:1163
 submit_bh_wbc+0x6b6/0x900 fs/buffer.c:3095
 submit_bh fs/buffer.c:3101 [inline]
 __bread_slow fs/buffer.c:1177 [inline]
 __bread_gfp+0x164/0x370 fs/buffer.c:1359
 sb_bread include/linux/buffer_head.h:307 [inline]
 fat_fill_super+0x353/0x3890 fs/fat/inode.c:1641
 msdos_fill_super+0x2f/0x40 fs/fat/namei_msdos.c:653
 mount_bdev+0x304/0x3c0 fs/super.c:1283
 msdos_mount+0x35/0x40 fs/fat/namei_msdos.c:660
 legacy_get_tree+0x108/0x220 fs/fs_context.c:661
 vfs_get_tree+0x8e/0x390 fs/super.c:1413
 do_new_mount fs/namespace.c:2791 [inline]
 do_mount+0x13b3/0x1c30 fs/namespace.c:3111
 ksys_mount+0xdb/0x150 fs/namespace.c:3320
 __do_sys_mount fs/namespace.c:3334 [inline]
 __se_sys_mount fs/namespace.c:3331 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3331
 do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c33a
Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 9d 8d fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 7a 8d fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007f6ce74e5a88 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f6ce74e5b40 RCX: 000000000045c33a
RDX: 00007f6ce74e5ae0 RSI: 0000000020000340 RDI: 00007f6ce74e5b00
RBP: 0000000000000000 R08: 00007f6ce74e5b40 R09: 00007f6ce74e5ae0
R10: 0000000000004000 R11: 0000000000000206 R12: 0000000000000003
R13: 00000000004c8abc R14: 00000000004dfa38 R15: 00000000ffffffff

Allocated by task 9145:
 save_stack+0x23/0x90 mm/kasan/common.c:69
 set_track mm/kasan/common.c:77 [inline]
 __kasan_kmalloc mm/kasan/common.c:493 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:466
 kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:501
 slab_post_alloc_hook mm/slab.h:520 [inline]
 slab_alloc mm/slab.c:3319 [inline]
 kmem_cache_alloc+0x121/0x710 mm/slab.c:3483
 __d_alloc+0x2e/0x8c0 fs/dcache.c:1688
 d_alloc+0x4d/0x280 fs/dcache.c:1767
 __lookup_hash+0xcd/0x190 fs/namei.c:1540
 filename_create+0x1a7/0x4f0 fs/namei.c:3635
 user_path_create fs/namei.c:3692 [inline]
 do_symlinkat+0xf3/0x290 fs/namei.c:4147
 __do_sys_symlink fs/namei.c:4173 [inline]
 __se_sys_symlink fs/namei.c:4171 [inline]
 __x64_sys_symlink+0x59/0x80 fs/namei.c:4171
 do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8720:
 save_stack+0x23/0x90 mm/kasan/common.c:69
 set_track mm/kasan/common.c:77 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:455
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:463
 __cache_free mm/slab.c:3425 [inline]
 kmem_cache_free+0x86/0x320 mm/slab.c:3693
 __d_free+0x20/0x30 fs/dcache.c:271
 __rcu_reclaim kernel/rcu/rcu.h:222 [inline]
 rcu_do_batch kernel/rcu/tree.c:2114 [inline]
 rcu_core+0x67f/0x1580 kernel/rcu/tree.c:2314
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2323
 __do_softirq+0x262/0x98c kernel/softirq.c:292

The buggy address belongs to the object at ffff88803e920160
 which belongs to the cache dentry(102:syz5) of size 288
The buggy address is located 88 bytes inside of
 288-byte region [ffff88803e920160, ffff88803e920280)
The buggy address belongs to the page:
page:ffffea0000fa4800 refcount:1 mapcount:0 mapping:ffff888096ce0c40 index:0xffff88803e9206e0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0001344d08 ffffea0000fa2bc8 ffff888096ce0c40
raw: ffff88803e9206e0 ffff88803e920000 000000010000000a 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88803e920080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88803e920100: fb fb fb fb fc fc fc fc fc fc fc fc fb fb fb fb
>ffff88803e920180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                        ^
 ffff88803e920200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88803e920280: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
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