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BUG: KASAN: use-after-free in link_path_walk+0x1198/0x18e0 fs/namei.c:2063
Read of size 1 at addr ffff8801d1793282 by task syz-executor3/31766

CPU: 0 PID: 31766 Comm: syz-executor3 Not tainted 4.13.0-rc2+ #1
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x145/0x1e1 lib/dump_stack.c:52
 print_address_description.cold.7+0x9/0x1c9 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report.cold.8+0x121/0x2da mm/kasan/report.c:408
 __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:426
 link_path_walk+0x1198/0x18e0 fs/namei.c:2063
 path_lookupat.isra.39+0x1a1/0xc00 fs/namei.c:2301
 filename_lookup+0x22e/0x480 fs/namei.c:2336
 user_path_at_empty+0x31/0x40 fs/namei.c:2590
 user_path include/linux/namei.h:61 [inline]
 do_mount+0x119/0x2c20 fs/namespace.c:2721
 SYSC_mount fs/namespace.c:2992 [inline]
 SyS_mount+0xb8/0xd0 fs/namespace.c:2969
 entry_SYSCALL_64_fastpath+0x23/0xc2
RIP: 0033:0x4576b9
RSP: 002b:00007fb8e2ed1c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00000000004576b9
RDX: 0000000020000040 RSI: 0000000020000000 RDI: 0000000000000000
RBP: 0000000000000082 R08: 0000000020000340 R09: 0000000000000000
R10: 0000000000200000 R11: 0000000000000246 R12: 000000000072bf0c
R13: 00007ffc5d5c192f R14: 00007fb8e2ed29c0 R15: 0000000000000000

Allocated by task 31776:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:551
 __do_kmalloc mm/slab.c:3725 [inline]
 __kmalloc_track_caller+0x143/0x7a0 mm/slab.c:3740
 kstrdup+0x2c/0x60 mm/util.c:56
 bpf_symlink+0x1e/0x100 kernel/bpf/inode.c:200
 vfs_symlink+0x2f4/0x520 fs/namei.c:4107
 SYSC_symlinkat fs/namei.c:4134 [inline]
 SyS_symlinkat fs/namei.c:4114 [inline]
 SYSC_symlink fs/namei.c:4147 [inline]
 SyS_symlink+0x1a9/0x210 fs/namei.c:4145
 entry_SYSCALL_64_fastpath+0x23/0xc2

Freed by task 31781:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3503 [inline]
 kfree+0xcc/0x270 mm/slab.c:3820
 bpf_evict_inode+0xe8/0x120 kernel/bpf/inode.c:375
 evict+0x452/0x9d0 fs/inode.c:553
 iput_final fs/inode.c:1514 [inline]
 iput+0x52c/0xad0 fs/inode.c:1541
 do_unlinkat+0x5f8/0x910 fs/namei.c:4049
 SYSC_unlink fs/namei.c:4090 [inline]
 SyS_unlink+0x11/0x20 fs/namei.c:4088
 entry_SYSCALL_64_fastpath+0x23/0xc2

The buggy address belongs to the object at ffff8801d1793280
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 2 bytes inside of
 32-byte region [ffff8801d1793280, ffff8801d17932a0)
The buggy address belongs to the page:
page:ffffea000745e4c0 count:1 mapcount:0 mapping:ffff8801d1793000 index:0xffff8801d1793fc1
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801d1793000 ffff8801d1793fc1 0000000100000020
raw: ffffea00074161a0 ffffea000740b9a0 ffff8801da8001c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d1793180: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8801d1793200: fb fb fb fb fc fc fc fc 00 fc fc fc fc fc fc fc
>ffff8801d1793280: fb fb fb fb fc fc fc fc 00 fc fc fc fc fc fc fc
                   ^
 ffff8801d1793300: 05 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8801d1793380: 00 01 fc fc fc fc fc fc fb fb fb fb fc fc fc fc
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