[Linux Kernel Bug] KASAN: slab-out-of-bounds Read in hfsplus_strcasecmp

[Jiaming Zhang]

Dear Linux kernel developers and maintainers:

We are writing to report a slab-out-of-bounds bug discovered in the
hfsplus subsystem with our modified syzkaller. This bug is
reproducible on the latest version (v6.17-rc6, commit
f83ec76bf285bea5727f478a68b894f5543ca76e).

The kernel console output, kernel config, syzkaller reproducer, and C
reproducer are attached to this email to help analysis. The KASAN
report from v6.17-rc6, formatted by syz-symbolize, is listed below:

hfsplus: invalid length 63743 has been corrected to 255
==================================================================
BUG: KASAN: slab-out-of-bounds in hfsplus_strcasecmp+0x1bc/0x490
fs/hfsplus/unicode.c:47
Read of size 2 at addr ffff88804b8d640c by task repro.out/9757

CPU: 1 UID: 0 PID: 9757 Comm: repro.out Not tainted 6.17.0-rc6 #1 PREEMPT(full)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x1c1/0x2a0 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0x17e/0x810 mm/kasan/report.c:482
kasan_report+0x147/0x180 mm/kasan/report.c:595
hfsplus_strcasecmp+0x1bc/0x490 fs/hfsplus/unicode.c:47
hfs_find_rec_by_key+0xa6/0x1e0 fs/hfsplus/bfind.c:89
__hfsplus_brec_find+0x18b/0x480 fs/hfsplus/bfind.c:124
hfsplus_brec_find+0x289/0x500 fs/hfsplus/bfind.c:184
hfsplus_brec_read+0x2b/0x120 fs/hfsplus/bfind.c:211
hfsplus_lookup+0x2aa/0x890 fs/hfsplus/dir.c:52
__lookup_slow+0x294/0x3d0 fs/namei.c:1808
lookup_slow+0x53/0x70 fs/namei.c:1825
walk_component+0x2d4/0x400 fs/namei.c:2129
lookup_last fs/namei.c:2630 [inline]
path_lookupat+0x163/0x430 fs/namei.c:2654
filename_lookup+0x212/0x570 fs/namei.c:2683
user_path_at+0x3a/0x60 fs/namei.c:3127
ksys_umount fs/namespace.c:2112 [inline]
__do_sys_umount fs/namespace.c:2120 [inline]
__se_sys_umount fs/namespace.c:2118 [inline]
__x64_sys_umount+0xee/0x160 fs/namespace.c:2118
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf3/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x452627
Code: 06 00 48 83 c4 08 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 c3 66
2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 a6 00 00 00 0f 05 <48> 3d
01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc5dd08ae8 EFLAGS: 00000206 ORIG_RAX: 00000000000000a6
RAX: ffffffffffffffda RBX: 00000000004004a0 RCX: 0000000000452627
RDX: 0000000000000009 RSI: 0000000000000009 RDI: 00007ffc5dd08b90
RBP: 00007ffc5dd09bd0 R08: 0000000000000015 R09: 00007ffc5dd08980
R10: 00000000004b9560 R11: 0000000000000206 R12: 000000000040a070
R13: 0000000000000000 R14: 00000000004bc018 R15: 00000000004004a0
</TASK>

Allocated by task 9757:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
kasan_kmalloc include/linux/kasan.h:260 [inline]
__do_kmalloc_node mm/slub.c:4376 [inline]
__kmalloc_noprof+0x27a/0x4f0 mm/slub.c:4388
kmalloc_noprof include/linux/slab.h:909 [inline]
hfsplus_find_init+0x8c/0x1d0 fs/hfsplus/bfind.c:21
hfsplus_lookup+0x19c/0x890 fs/hfsplus/dir.c:44
__lookup_slow+0x294/0x3d0 fs/namei.c:1808
lookup_slow+0x53/0x70 fs/namei.c:1825
walk_component+0x2d4/0x400 fs/namei.c:2129
lookup_last fs/namei.c:2630 [inline]
path_lookupat+0x163/0x430 fs/namei.c:2654
filename_lookup+0x212/0x570 fs/namei.c:2683
user_path_at+0x3a/0x60 fs/namei.c:3127
ksys_umount fs/namespace.c:2112 [inline]
__do_sys_umount fs/namespace.c:2120 [inline]
__se_sys_umount fs/namespace.c:2118 [inline]
__x64_sys_umount+0xee/0x160 fs/namespace.c:2118
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf3/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88804b8d6000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 0 bytes to the right of
allocated 1036-byte region [ffff88804b8d6000, ffff88804b8d640c)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4b8d0
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0x4fff00000000040(head|node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000040 ffff88801a442000 0000000000000000 dead000000000001
raw: 0000000000000000 0000000080080008 00000000f5000000 0000000000000000
head: 04fff00000000040 ffff88801a442000 0000000000000000 dead000000000001
head: 0000000000000000 0000000080080008 00000000f5000000 0000000000000000
head: 04fff00000000003 ffffea00012e3401 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask
0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC),
pid 8133, tgid 8133 (sh), ts 23500816499, free_ts 23484371257
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:2492 [inline]
allocate_slab+0x8a/0x370 mm/slub.c:2660
new_slab mm/slub.c:2714 [inline]
___slab_alloc+0xbeb/0x1420 mm/slub.c:3901
__slab_alloc mm/slub.c:3992 [inline]
__slab_alloc_node mm/slub.c:4067 [inline]
slab_alloc_node mm/slub.c:4228 [inline]
__do_kmalloc_node mm/slub.c:4375 [inline]
__kmalloc_noprof+0x305/0x4f0 mm/slub.c:4388
kmalloc_noprof include/linux/slab.h:909 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
tomoyo_init_log+0x1a32/0x1f30 security/tomoyo/audit.c:275
tomoyo_supervisor+0x340/0x1490 security/tomoyo/common.c:2198
tomoyo_audit_env_log security/tomoyo/environ.c:36 [inline]
tomoyo_env_perm+0x149/0x1e0 security/tomoyo/environ.c:63
tomoyo_environ security/tomoyo/domain.c:672 [inline]
tomoyo_find_next_domain+0x15cf/0x1aa0 security/tomoyo/domain.c:888
tomoyo_bprm_check_security+0x11c/0x180 security/tomoyo/tomoyo.c:102
security_bprm_check+0x89/0x270 security/security.c:1302
search_binary_handler fs/exec.c:1660 [inline]
exec_binprm fs/exec.c:1702 [inline]
bprm_execve+0x8ee/0x1450 fs/exec.c:1754
do_execveat_common+0x521/0x6b0 fs/exec.c:1860
do_execve fs/exec.c:1934 [inline]
__do_sys_execve fs/exec.c:2010 [inline]
__se_sys_execve fs/exec.c:2005 [inline]
__x64_sys_execve+0x94/0xb0 fs/exec.c:2005
page last free pid 5289 tgid 5289 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbc0/0xd40 mm/page_alloc.c:2895
discard_slab mm/slub.c:2758 [inline]
__put_partials+0x156/0x1a0 mm/slub.c:3223
put_cpu_partial+0x17c/0x250 mm/slub.c:3298
__slab_free+0x2d5/0x3c0 mm/slub.c:4565
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:340
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4191 [inline]
slab_alloc_node mm/slub.c:4240 [inline]
kmem_cache_alloc_node_noprof+0x1bb/0x3c0 mm/slub.c:4292
__alloc_skb+0x12a/0x2f0 net/core/skbuff.c:659
netlink_sendmsg+0x5c6/0xb30 net/netlink/af_netlink.c:1871
sock_sendmsg_nosec net/socket.c:714 [inline]
__sock_sendmsg+0x219/0x270 net/socket.c:729
____sys_sendmsg+0x507/0x840 net/socket.c:2614
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
__sys_sendmsg net/socket.c:2700 [inline]
__do_sys_sendmsg net/socket.c:2705 [inline]
__se_sys_sendmsg net/socket.c:2703 [inline]
__x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf3/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88804b8d6300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88804b8d6380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88804b8d6400: 00 04 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88804b8d6480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88804b8d6500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Please let me know if any further information is required.

Best Regards,
Jiaming Zhang.

[Viacheslav Dubeyko]

On Mon, 2025-09-15 at 11:04 +0800, Jiaming Zhang wrote:
> Dear Linux kernel developers and maintainers:
>
> We are writing to report a slab-out-of-bounds bug discovered in the
> hfsplus subsystem with our modified syzkaller. This bug is
> reproducible on the latest version (v6.17-rc6, commit
> f83ec76bf285bea5727f478a68b894f5543ca76e).
>

Thank you for the report. Issue has been created:

https://github.com/hfs-linux-kernel/hfs-linux-kernel/issues/238

Thanks,
Slava.