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

[syzbot]

syzbot has found reproducer for the following crash on upstream commit
a27fc14219f2e3c4a46ba9177b04d9b52c875532 (Mon Apr 16 21:07:39 2018 +0000)
Merge branch 'parisc-4.17-3' of  
git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=b890b3335a4d8c608963

So far this crash happened 3 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=4639432657338368
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=5739177354199040
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5837965024559104
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-5914490758943236750
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b890b3335a4d8c608963@xxxxxxxxxxxxxxxxxxxxxxxxx
It will help syzbot understand when the bug is fixed.

VFS: Can't find a Minix filesystem V1 | V2 | V3 on device loop5.
==================================================================
BUG: KASAN: global-out-of-bounds in string+0x291/0x2c0 lib/vsprintf.c:608
Write of size 1 at addr ffffffff8a5405c0 by task syzkaller915239/4487

CPU: 1 PID: 4487 Comm: syzkaller915239 Not tainted 4.17.0-rc1+ #6
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:2292
 vsprintf+0x2a/0x40 lib/vsprintf.c:2472
 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:1165
 get_super_block+0x34/0x40 fs/reiserfs/super.c:2605
 mount_fs+0xae/0x328 fs/super.c:1268
 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:2517 [inline]
 do_mount+0x564/0x3070 fs/namespace.c:2847
 ksys_mount+0x12d/0x140 fs/namespace.c:3063
 __do_sys_mount fs/namespace.c:3077 [inline]
 __se_sys_mount fs/namespace.c:3074 [inline]
 __x64_sys_mount+0xbe/0x150 fs/namespace.c:3074
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x448bca
RSP: 002b:00007f33571ccc68 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000020000040 RCX: 0000000000448bca
RDX: 0000000020000000 RSI: 0000000020000040 RDI: 00007f33571ccc80
RBP: 0000000000000004 R08: 0000000020000380 R09: 000000000000000a
R10: 0000000001000000 R11: 0000000000000202 R12: 0000000000000043
R13: 0000000000000044 R14: 0000000001000000 R15: 0000000000000004

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

Memory state around the buggy address:
 ffffffff8a540480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffffff8a540500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffffffff8a540580: 00 00 00 00 00 00 00 00 fa fa fa fa 04 fa fa fa
                                           ^
 ffffffff8a540600: fa fa fa fa 00 fa fa fa fa fa fa fa 00 fa fa fa
 ffffffff8a540680: fa fa fa fa 00 fa fa fa fa fa fa fa 00 fa fa fa
==================================================================