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BUG: KASAN: slab-out-of-bounds in vsscanf+0x2666/0x2ef0 lib/vsprintf.c:3275
Read of size 1 at addr ffff8880a878bc42 by task syz-executor.5/29683

CPU: 0 PID: 29683 Comm: syz-executor.5 Not tainted 5.6.0-rc7-syzkaller #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+0x1e9/0x30e lib/dump_stack.c:118
 print_address_description+0x74/0x5c0 mm/kasan/report.c:374
 __kasan_report+0x14b/0x1c0 mm/kasan/report.c:506
 kasan_report+0x25/0x50 mm/kasan/common.c:641
 vsscanf+0x2666/0x2ef0 lib/vsprintf.c:3275
 sscanf+0x6c/0x90 lib/vsprintf.c:3481
 smk_set_cipso+0x1ac/0x6a0 security/smack/smackfs.c:881
 do_loop_readv_writev fs/read_write.c:717 [inline]
 do_iter_write+0x426/0x570 fs/read_write.c:1000
 vfs_writev fs/read_write.c:1071 [inline]
 do_writev+0x239/0x490 fs/read_write.c:1114
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c849
Code: ad b6 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 b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f96d18c5c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f96d18c66d4 RCX: 000000000045c849
RDX: 0000000000000001 RSI: 0000000020000300 RDI: 0000000000000003
RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000d12 R14: 00000000004cb1d9 R15: 000000000076bf0c

Allocated by task 29683:
 save_stack mm/kasan/common.c:72 [inline]
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc+0x118/0x1c0 mm/kasan/common.c:515
 __do_kmalloc mm/slab.c:3656 [inline]
 __kmalloc_track_caller+0x249/0x320 mm/slab.c:3671
 memdup_user_nul+0x26/0xf0 mm/util.c:259
 smk_set_cipso+0xff/0x6a0 security/smack/smackfs.c:859
 do_loop_readv_writev fs/read_write.c:717 [inline]
 do_iter_write+0x426/0x570 fs/read_write.c:1000
 vfs_writev fs/read_write.c:1071 [inline]
 do_writev+0x239/0x490 fs/read_write.c:1114
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 29172:
 save_stack mm/kasan/common.c:72 [inline]
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:337 [inline]
 __kasan_slab_free+0x12e/0x1e0 mm/kasan/common.c:476
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x220 mm/slab.c:3757
 security_inode_init_security+0x268/0x300 security/security.c:1031
 shmem_symlink+0xc8/0x6f0 mm/shmem.c:3114
 vfs_symlink+0x36f/0x500 fs/namei.c:4201
 do_symlinkat+0x18b/0x420 fs/namei.c:4228
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a878bc40
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 2 bytes inside of
 32-byte region [ffff8880a878bc40, ffff8880a878bc60)
The buggy address belongs to the page:
page:ffffea0002a1e2c0 refcount:1 mapcount:0 mapping:ffff8880aa4001c0 index:0xffff8880a878bfc1
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0002204ac8 ffffea00027bb048 ffff8880aa4001c0
raw: ffff8880a878bfc1 ffff8880a878b000 000000010000003f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a878bb00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8880a878bb80: fb fb fb fb fc fc fc fc 07 fc fc fc fc fc fc fc
>ffff8880a878bc00: 07 fc fc fc fc fc fc fc 02 fc fc fc fc fc fc fc
                                           ^
 ffff8880a878bc80: 07 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8880a878bd00: fb fb fb fb fc fc fc fc 07 fc fc fc fc fc fc fc
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