KASAN: use-after-free Read in search_by_entry_key

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cbfa1702 Linux 4.14.198
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=133a71c5900000
kernel config: https://syzkaller.appspot.com/x/.config?x=3990958d85b55e59
dashboard link: https://syzkaller.appspot.com/bug?extid=c78d28ac5472f784e38b
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1301cf65900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14c7c6c3900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c78d28...@syzkaller.appspotmail.com

REISERFS (device loop0): journal params: device loop0, size 15748, journal first block 18, max trans len 256, max batch 225, max commit age 30, max trans age 30
REISERFS (device loop0): checking transaction log (loop0)
REISERFS (device loop0): Using tea hash to sort names
REISERFS (device loop0): using 3.5.x disk format
==================================================================
BUG: KASAN: use-after-free in bin_search_in_dir_item fs/reiserfs/namei.c:40 [inline]
BUG: KASAN: use-after-free in search_by_entry_key+0xc87/0xf70 fs/reiserfs/namei.c:164
Read of size 4 at addr ffff888078a1c7bd by task syz-executor396/6350

CPU: 0 PID: 6350 Comm: syz-executor396 Not tainted 4.14.198-syzkaller #0
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+0x1b2/0x283 lib/dump_stack.c:58
print_address_description.cold+0x54/0x1d3 mm/kasan/report.c:252
kasan_report_error.cold+0x8a/0x194 mm/kasan/report.c:351
kasan_report mm/kasan/report.c:409 [inline]
__asan_report_load_n_noabort+0x6b/0x80 mm/kasan/report.c:440
bin_search_in_dir_item fs/reiserfs/namei.c:40 [inline]
search_by_entry_key+0xc87/0xf70 fs/reiserfs/namei.c:164
reiserfs_find_entry.part.0+0x138/0x1200 fs/reiserfs/namei.c:321
reiserfs_find_entry fs/reiserfs/namei.c:367 [inline]
reiserfs_lookup+0x1fd/0x400 fs/reiserfs/namei.c:367
lookup_real fs/namei.c:1555 [inline]
__lookup_hash fs/namei.c:1575 [inline]
__lookup_hash+0x1bb/0x270 fs/namei.c:1563
lookup_one_len+0x279/0x3a0 fs/namei.c:2539
reiserfs_lookup_privroot+0x92/0x270 fs/reiserfs/xattr.c:963
reiserfs_fill_super+0x1ad8/0x28b6 fs/reiserfs/super.c:2179
mount_bdev+0x2b3/0x360 fs/super.c:1134
mount_fs+0x92/0x2a0 fs/super.c:1237
vfs_kern_mount.part.0+0x5b/0x470 fs/namespace.c:1046
vfs_kern_mount fs/namespace.c:1036 [inline]
do_new_mount fs/namespace.c:2549 [inline]
do_mount+0xe53/0x2a00 fs/namespace.c:2879
SYSC_mount fs/namespace.c:3095 [inline]
SyS_mount+0xa8/0x120 fs/namespace.c:3072
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x44706a
RSP: 002b:00007ffeabc83998 EFLAGS: 00000297 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffeabc839f0 RCX: 000000000044706a
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007ffeabc839b0
RBP: 00007ffeabc839b0 R08: 00007ffeabc839f0 R09: 00007ffe00000015
R10: 0000000000000000 R11: 0000000000000297 R12: 0000000000000006
R13: 0000000000000004 R14: 0000000000000003 R15: 0000000000000003

The buggy address belongs to the page:
page:ffffea0001e28700 count:0 mapcount:0 mapping: (null) index:0x1
flags: 0xfffe0000000000()
raw: 00fffe0000000000 0000000000000000 0000000000000001 00000000ffffffff
raw: ffffea0001e28760 ffff8880aea2ed48 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888078a1c680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888078a1c700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888078a1c780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff888078a1c800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888078a1c880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


---
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[syzbot]

syzbot suspects this issue was fixed by commit:

commit b74d5f70523a819aac71e0eee4f4b530e69e463a
Author: Rustam Kovhaev <rkov...@gmail.com>
Date: Sun Nov 1 14:09:58 2020 +0000

reiserfs: add check for an invalid ih_entry_count

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=141f61f2d00000
start commit: cbfa1702 Linux 4.14.198
git tree: linux-4.14.y

kernel config: https://syzkaller.appspot.com/x/.config?x=3990958d85b55e59
dashboard link: https://syzkaller.appspot.com/bug?extid=c78d28ac5472f784e38b

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=174503c3900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14596187900000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: reiserfs: add check for an invalid ih_entry_count

For information about bisection process see: https://goo.gl/tpsmEJ#bisection