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BUG: KASAN: use-after-free in link_path_walk+0x104f/0x1220 fs/namei.c:2085
Read of size 4 at addr ffff8801d9c2e000 by task syz-executor0/5041

CPU: 0 PID: 5041 Comm: syz-executor0 Not tainted 4.9.77-g8788313 #16
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d54ef970 ffffffff81d941c9 ffffea0007670b80 ffff8801d9c2e000
 0000000000000000 ffff8801d9c2e000 ffff8801d54efd30 ffff8801d54ef9a8
 ffffffff8153db93 ffff8801d9c2e000 0000000000000004 0000000000000000
Call Trace:
 [<ffffffff81d941c9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d941c9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff8153db93>] print_address_description+0x73/0x280 mm/kasan/report.c:252
 [<ffffffff8153e0b5>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff8153e0b5>] kasan_report+0x275/0x360 mm/kasan/report.c:408
 [<ffffffff8153e1f4>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff815a006f>] link_path_walk+0x104f/0x1220 fs/namei.c:2085
 [<ffffffff815a03fa>] path_lookupat+0x6a/0x3f0 fs/namei.c:2280
 [<ffffffff815a2140>] do_o_path fs/namei.c:3491 [inline]
 [<ffffffff815a2140>] path_openat+0x19c0/0x2910 fs/namei.c:3520
 [<ffffffff815a6887>] do_filp_open+0x197/0x290 fs/namei.c:3566
 [<ffffffff8156b082>] do_sys_open+0x352/0x4c0 fs/open.c:1072
 [<ffffffff8156b260>] SYSC_openat fs/open.c:1099 [inline]
 [<ffffffff8156b260>] SyS_openat+0x30/0x40 fs/open.c:1093
 [<ffffffff838b2b6e>] entry_SYSCALL_64_fastpath+0x29/0xe8

Allocated by task 5040:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:505
 set_track mm/kasan/kasan.c:517 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:609
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:547
 slab_post_alloc_hook mm/slab.h:417 [inline]
 slab_alloc_node mm/slub.c:2715 [inline]
 slab_alloc mm/slub.c:2723 [inline]
 kmem_cache_alloc+0xba/0x290 mm/slub.c:2728
 __d_alloc+0x2e/0x8f0 fs/dcache.c:1593
 d_make_root+0x3f/0x80 fs/dcache.c:1882
 ramfs_fill_super+0x35f/0x4a0 fs/ramfs/inode.c:233
 mount_nodev+0x59/0x100 fs/super.c:1142
 ramfs_mount+0x2c/0x40 fs/ramfs/inode.c:243
 mount_fs+0x27f/0x350 fs/super.c:1202
 vfs_kern_mount.part.21+0xd0/0x3e0 fs/namespace.c:991
 vfs_kern_mount fs/namespace.c:2509 [inline]
 do_new_mount fs/namespace.c:2512 [inline]
 do_mount+0x3e1/0x28b0 fs/namespace.c:2834
 SYSC_mount fs/namespace.c:3050 [inline]
 SyS_mount+0xab/0x120 fs/namespace.c:3027
 entry_SYSCALL_64_fastpath+0x29/0xe8

Freed by task 5040:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:505
 set_track mm/kasan/kasan.c:517 [inline]
 kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:582
 slab_free_hook mm/slub.c:1355 [inline]
 slab_free_freelist_hook mm/slub.c:1377 [inline]
 slab_free mm/slub.c:2958 [inline]
 kmem_cache_free+0xc7/0x300 mm/slub.c:2980
 __d_free fs/dcache.c:265 [inline]
 dentry_free+0xd5/0x150 fs/dcache.c:341
 __dentry_kill+0x343/0x480 fs/dcache.c:579
 dentry_kill fs/dcache.c:606 [inline]
 dput.part.23+0x680/0x7b0 fs/dcache.c:818
 dput fs/dcache.c:780 [inline]
 do_one_tree+0x43/0x50 fs/dcache.c:1476
 shrink_dcache_for_umount+0x67/0x160 fs/dcache.c:1490
 generic_shutdown_super+0x6d/0x340 fs/super.c:422
 kill_anon_super fs/super.c:964 [inline]
 kill_litter_super+0x72/0x90 fs/super.c:974
 ramfs_kill_sb+0x3f/0x50 fs/ramfs/inode.c:249
 deactivate_locked_super+0x88/0xd0 fs/super.c:310
 deactivate_super+0x91/0xd0 fs/super.c:341
 cleanup_mnt+0xb2/0x160 fs/namespace.c:1133
 __cleanup_mnt+0x16/0x20 fs/namespace.c:1140
 task_work_run+0x115/0x190 kernel/task_work.c:116
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0xfc/0x120 arch/x86/entry/common.c:160
 prepare_exit_to_usermode arch/x86/entry/common.c:190 [inline]
 syscall_return_slowpath+0x1a0/0x1e0 arch/x86/entry/common.c:259
 entry_SYSCALL_64_fastpath+0xe6/0xe8

The buggy address belongs to the object at ffff8801d9c2e000
 which belongs to the cache dentry of size 288
The buggy address is located 0 bytes inside of
 288-byte region [ffff8801d9c2e000, ffff8801d9c2e120)
The buggy address belongs to the page:
page:ffffea0007670b80 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x8000000000004080(slab|head)
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d9c2df00: fc fc fc fc 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801d9c2df80: 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801d9c2e000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8801d9c2e080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d9c2e100: fb fb fb fb fc fc fc fc fc fc fc fc 00 00 00 00
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