KASAN: slab-out-of-bounds Read in squashfs_export_iget

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a9e26cb5 Add linux-next specific files for 20201208
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1674f80f500000
kernel config: https://syzkaller.appspot.com/x/.config?x=e259434a8eaf0206
dashboard link: https://syzkaller.appspot.com/bug?extid=04419e3ff19d2970ea28
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=136a6adf500000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10457ccb500000

The issue was bisected to:

commit 555f63cd88404e122e8d31d0f925e430bd3f32d9
Author: Alexander Potapenko <gli...@google.com>
Date: Fri Dec 4 03:19:29 2020 +0000

mm, kfence: insert KFENCE hooks for SLUB

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1619bb7f500000
final oops: https://syzkaller.appspot.com/x/report.txt?x=1519bb7f500000
console output: https://syzkaller.appspot.com/x/log.txt?x=1119bb7f500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+04419e...@syzkaller.appspotmail.com
Fixes: 555f63cd8840 ("mm, kfence: insert KFENCE hooks for SLUB")

loop0: detected capacity change from 264192 to 0
==================================================================
BUG: KASAN: slab-out-of-bounds in squashfs_inode_lookup fs/squashfs/export.c:44 [inline]
BUG: KASAN: slab-out-of-bounds in squashfs_export_iget+0x274/0x2a0 fs/squashfs/export.c:69
Read of size 8 at addr ffff88801c6f6e08 by task syz-executor839/8488

CPU: 0 PID: 8488 Comm: syz-executor839 Not tainted 5.10.0-rc7-next-20201208-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x107/0x163 lib/dump_stack.c:120
print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:230
__kasan_report mm/kasan/report.c:396 [inline]
kasan_report.cold+0x79/0xd5 mm/kasan/report.c:413
squashfs_inode_lookup fs/squashfs/export.c:44 [inline]
squashfs_export_iget+0x274/0x2a0 fs/squashfs/export.c:69
squashfs_fh_to_dentry fs/squashfs/export.c:84 [inline]
squashfs_fh_to_dentry+0x78/0xb0 fs/squashfs/export.c:77
exportfs_decode_fh_raw+0x127/0x7a0 fs/exportfs/expfs.c:436
exportfs_decode_fh+0x38/0x90 fs/exportfs/expfs.c:575
do_handle_to_path fs/fhandle.c:152 [inline]
handle_to_path fs/fhandle.c:207 [inline]
do_handle_open+0x2b6/0x7f0 fs/fhandle.c:223
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4443d9
Code: 8d d7 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 5b d7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffd937fcd78 EFLAGS: 00000246 ORIG_RAX: 0000000000000130
RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 00000000004443d9
RDX: 0000000000000000 RSI: 0000000020000280 RDI: 0000000000000005
RBP: 00000000006cf018 R08: 00007ffd00000015 R09: 00000000004002e0
R10: 00007ffd937fcc20 R11: 0000000000000246 R12: 0000000000401fc0
R13: 0000000000402050 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 6500:
kasan_save_stack+0x1b/0x40 mm/kasan/common.c:39
kasan_set_track mm/kasan/common.c:47 [inline]
set_alloc_info mm/kasan/common.c:405 [inline]
____kasan_kmalloc mm/kasan/common.c:436 [inline]
____kasan_kmalloc.constprop.0+0xa0/0xd0 mm/kasan/common.c:408
kmalloc include/linux/slab.h:570 [inline]
kzalloc include/linux/slab.h:695 [inline]
lsm_cred_alloc security/security.c:534 [inline]
security_prepare_creds+0x10e/0x190 security/security.c:1633
prepare_creds+0x509/0x730 kernel/cred.c:285
access_override_creds fs/open.c:353 [inline]
do_faccessat+0x3d7/0x870 fs/open.c:417
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff88801c6f6de8
which belongs to the cache kmalloc-8 of size 8
The buggy address is located 24 bytes to the right of
8-byte region [ffff88801c6f6de8, ffff88801c6f6df0)
The buggy address belongs to the page:
page:0000000061a643f0 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88801c6f6de8 pfn:0x1c6f6
flags: 0xfff00000000200(slab)
raw: 00fff00000000200 ffffea0000625500 0000000500000005 ffff888010841c80
raw: ffff88801c6f6de8 000000008066005d 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88801c6f6d00: fc fc fc fc fb fc fc fc fc fb fc fc fc fc fb fc
ffff88801c6f6d80: fc fc fc fb fc fc fc fc fa fc fc fc fc fb fc fc
>ffff88801c6f6e00: fc fc 00 fc fc fc fc fa fc fc fc fc fb fc fc fc
^
ffff88801c6f6e80: fc 00 fc fc fc fc fa fc fc fc fc fb fc fc fc fc
ffff88801c6f6f00: 00 fc fc fc fc fa fc fc fc fc fb fc fc fc fc fb
==================================================================


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
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[Marco Elver]

On Thu, 10 Dec 2020 at 11:43, syzbot
<syzbot+04419e...@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: a9e26cb5 Add linux-next specific files for 20201208
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1674f80f500000
> kernel config: https://syzkaller.appspot.com/x/.config?x=e259434a8eaf0206
> dashboard link: https://syzkaller.appspot.com/bug?extid=04419e3ff19d2970ea28
> compiler: gcc (GCC) 10.1.0-syz 20200507
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=136a6adf500000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10457ccb500000
>
> The issue was bisected to:
>
> commit 555f63cd88404e122e8d31d0f925e430bd3f32d9
> Author: Alexander Potapenko <gli...@google.com>
> Date: Fri Dec 4 03:19:29 2020 +0000
>
> mm, kfence: insert KFENCE hooks for SLUB

This appears to be flaky bisection, and is not due to KFENCE.

It can be reproduced even with CONFIG_KFENCE=n, and also reverting
"mm, kfence: insert KFENCE hooks for SLUB" entirely.

Thanks,
-- Marco