KASAN: global-out-of-bounds Write in string

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
642e7fd23353e22290e3d51719fcb658dc252342 (Tue Apr 3 04:22:12 2018 +0000)
Merge branch 'syscalls-next' of  
git://git.kernel.org/pub/scm/linux/kernel/git/brodo/linux
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=b890b3335a4d8c608963

syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=4698588919627776
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5456053378482176
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-6874493495260513980
compiler: gcc (GCC) 7.1.1 20170620

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Reported-by: syzbot+b890b3335a4d8c608963@xxxxxxxxxxxxxxxxxxxxxxxxx
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IPVS: ftp: loaded support on port[0] = 21
REISERFS warning (device loop0): sh-2021 reiserfs_fill_super: can not find  
reiserfs on loop0
syz-executor0 (4503) used greatest stack depth: 15560 bytes left
REISERFS warning (device loop0): sh-2021 reiserfs_fill_super: can not find  
reiserfs on loop0
==================================================================
BUG: KASAN: global-out-of-bounds in string+0x1cb/0x200 lib/vsprintf.c:598
Write of size 1 at addr ffffffff89e166a0 by task syz-executor0/4522

CPU: 1 PID: 4522 Comm: syz-executor0 Not tainted 4.16.0+ #12
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1a7/0x27d lib/dump_stack.c:53
 print_address_description+0x178/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23c/0x360 mm/kasan/report.c:412
 __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:435
 string+0x1cb/0x200 lib/vsprintf.c:598
 vsnprintf+0x863/0x1900 lib/vsprintf.c:2282
 vsprintf+0x2a/0x40 lib/vsprintf.c:2462
 prepare_error_buf+0x1d2/0x1820 fs/reiserfs/prints.c:240
 __reiserfs_warning+0xc8/0x1a0 fs/reiserfs/prints.c:267
 reiserfs_getopt fs/reiserfs/super.c:1044 [inline]
 reiserfs_parse_options+0x11e5/0x24e0 fs/reiserfs/super.c:1194
 reiserfs_fill_super+0x520/0x33a0 fs/reiserfs/super.c:1946
 mount_bdev+0x2b7/0x370 fs/super.c:1119
 get_super_block+0x34/0x40 fs/reiserfs/super.c:2605
 mount_fs+0x66/0x2d0 fs/super.c:1222
 vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037
 vfs_kern_mount fs/namespace.c:2514 [inline]
 do_new_mount fs/namespace.c:2517 [inline]
 do_mount+0xea4/0x2b90 fs/namespace.c:2847
 ksys_mount+0xab/0x120 fs/namespace.c:3063
 SYSC_mount fs/namespace.c:3077 [inline]
 SyS_mount+0x39/0x50 fs/namespace.c:3074
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x457d0a
RSP: 002b:00007f0655cddbb8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000020000000 RCX: 0000000000457d0a
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f0655cddc00
RBP: 0000000000000004 R08: 0000000020013f00 R09: 0000000020000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
R13: 000000000000066d R14: 00000000006fcad8 R15: 0000000000000001

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

Memory state around the buggy address:
 ffffffff89e16580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffffff89e16600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffffffff89e16680: 00 00 00 00 fa fa fa fa 04 fa fa fa fa fa fa fa
                               ^
 ffffffff89e16700: 00 fa fa fa fa fa fa fa 00 fa fa fa fa fa fa fa
 ffffffff89e16780: 00 fa fa fa fa fa fa fa 00 fa fa fa fa fa fa fa
==================================================================


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