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BUG: KASAN: global-out-of-bounds in string+0x291/0x2c0 lib/vsprintf.c:608
Write of size 1 at addr ffffffff8a7c1620 by task syz-executor5/11015

CPU: 1 PID: 11015 Comm: syz-executor5 Not tainted 4.17.0-rc5+ #60
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+0x1b9/0x294 lib/dump_stack.c:113
 print_address_description+0x6c/0x20b mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
 __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:435
 string+0x291/0x2c0 lib/vsprintf.c:608
 vsnprintf+0x4b7/0x1b40 lib/vsprintf.c:2296
 vsprintf+0x2a/0x40 lib/vsprintf.c:2476
 prepare_error_buf+0x23b/0x1aa0 fs/reiserfs/prints.c:240
 __reiserfs_warning+0xb0/0xd0 fs/reiserfs/prints.c:267
 reiserfs_getopt fs/reiserfs/super.c:1044 [inline]
 reiserfs_parse_options+0x11f4/0x27f0 fs/reiserfs/super.c:1194
 reiserfs_fill_super+0x520/0x3900 fs/reiserfs/super.c:1946
 mount_bdev+0x30c/0x3e0 fs/super.c:1164
 get_super_block+0x34/0x40 fs/reiserfs/super.c:2605
 mount_fs+0xae/0x328 fs/super.c:1267
 vfs_kern_mount.part.34+0xd4/0x4d0 fs/namespace.c:1037
 vfs_kern_mount fs/namespace.c:1027 [inline]
 do_new_mount fs/namespace.c:2518 [inline]
 do_mount+0x564/0x3070 fs/namespace.c:2848
 ksys_mount+0x12d/0x140 fs/namespace.c:3064
 __do_sys_mount fs/namespace.c:3078 [inline]
 __se_sys_mount fs/namespace.c:3075 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3075
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45843a
RSP: 002b:00007fb881255ba8 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00000000200000c0 RCX: 000000000045843a
RDX: 00000000200000c0 RSI: 0000000020000100 RDI: 00007fb881255bf0
RBP: 0000000000000006 R08: 00000000200007c0 R09: 00000000200000c0
R10: 0000000002000000 R11: 0000000000000202 R12: 0000000000000016
R13: 0000000000000006 R14: 00000000006fed68 R15: 0000000000000000

The buggy address belongs to the variable:
 error_buf+0x400/0x420

Memory state around the buggy address:
 ffffffff8a7c1500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffffff8a7c1580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffffff8a7c1600: 00 00 00 00 fa fa fa fa 04 fa fa fa fa fa fa fa
                               ^
 ffffffff8a7c1680: 00 fa fa fa fa fa fa fa 00 fa fa fa fa fa fa fa
 ffffffff8a7c1700: 00 fa fa fa fa fa fa fa 00 fa fa fa fa fa fa fa
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