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

Status: fixed on 2021/03/10 01:48
Fix commit: eabac19e40c0 squashfs: add more sanity checks in inode lookup
First crash: 570d, last: 551d

Cause bisection: introduced by (bisect log) :
commit 555f63cd88404e122e8d31d0f925e430bd3f32d9
Author: Alexander Potapenko <>
Date: Fri Dec 4 03:19:29 2020 +0000

  mm, kfence: insert KFENCE hooks for SLUB

Crash: BUG: KFENCE: out-of-bounds in squashfs_export_iget (log)
Repro: C syz .config

Fix bisection: failed (bisect log)
similar bugs (2):
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.19 KASAN: slab-out-of-bounds Read in squashfs_export_iget C done 5 517d 617d 1/1 fixed on 2021/03/02 19:53
linux-4.14 KASAN: slab-out-of-bounds Read in squashfs_export_iget C done 4 525d 629d 1/1 fixed on 2021/02/25 13:45

Sample crash report:
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 ffff88801ba96700 by task syz-executor172/8473

CPU: 0 PID: 8473 Comm: syz-executor172 Not tainted 5.11.0-rc1-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
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:00007fffc3d35ac8 EFLAGS: 00000246 ORIG_RAX: 0000000000000130
RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 00000000004443d9
RDX: 0000000000000000 RSI: 0000000020000280 RDI: 0000000000000005
RBP: 00000000006cf018 R08: 00007fff00000015 R09: 00000000004002e0
R10: 00007fffc3d35970 R11: 0000000000000246 R12: 0000000000401fc0
R13: 0000000000402050 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 6487:
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:401 [inline]
 ____kasan_kmalloc.constprop.0+0x82/0xa0 mm/kasan/common.c:429
 kmalloc include/linux/slab.h:557 [inline]
 kzalloc include/linux/slab.h:682 [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+0x3d7/0x820 fs/open.c:417
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46

Freed by task 6487:
 kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
 kasan_set_track+0x1c/0x30 mm/kasan/common.c:46
 kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:354
 ____kasan_slab_free+0xe1/0x110 mm/kasan/common.c:362
 kasan_slab_free include/linux/kasan.h:188 [inline]
 slab_free_hook mm/slub.c:1547 [inline]
 slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1580
 slab_free mm/slub.c:3143 [inline]
 kfree+0xdb/0x360 mm/slub.c:4125
 security_cred_free+0xc3/0x130 security/security.c:1627
 put_cred_rcu+0x122/0x4e0 kernel/cred.c:114
 __put_cred+0x1de/0x250 kernel/cred.c:148
 put_cred include/linux/cred.h:287 [inline]
 put_cred include/linux/cred.h:280 [inline]
 revert_creds+0x1a8/0x1f0 kernel/cred.c:598
 do_faccessat+0x2ca/0x820 fs/open.c:464
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46

The buggy address belongs to the object at ffff88801ba966e0
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 24 bytes to the right of
 8-byte region [ffff88801ba966e0, ffff88801ba966e8)
The buggy address belongs to the page:
page:00000000327c546f refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88801ba965a0 pfn:0x1ba96
flags: 0xfff00000000200(slab)
raw: 00fff00000000200 ffffea0000793300 0000000d0000000d ffff888010041c80
raw: ffff88801ba965a0 000000008066005f 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88801ba96600: fc fc fc fa fc fc fc fc fb fc fc fc fc fa fc fc
 ffff88801ba96680: fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc fc
>ffff88801ba96700: fc 00 fc fc fc fc fb fc fc fc fc fa fc fc fc fc
 ffff88801ba96780: fa fc fc fc fc fa fc fc fc fc fa fc fc fc fc fa
 ffff88801ba96800: fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa fc

Crashes (3):
Manager Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Title
ci-upstream-kasan-gce-root 2020/12/28 13:17 upstream 5c8fe583cce5 2242f77f .config log report syz C
ci-upstream-kasan-gce-selinux-root 2020/12/16 01:08 upstream 148842c98a24 97183ed7 .config log report syz C
ci-upstream-linux-next-kasan-gce-root 2020/12/09 02:35 linux-next a9e26cb5f261 a7f7f4a4 .config log report syz C