hfsplus: fix slab-out-of-bounds read in hfsplus_uni2asc()
CVE: CVE-2025-38713
Component: kernel
CWE: CWE-125
Severity: Moderate
CVSS v3: 6.6/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:H
Release date: 2025-09-04T00:00:00+00:00

In the Linux kernel, the following vulnerability has been resolved:

hfsplus: fix slab-out-of-bounds read in hfsplus_uni2asc()

The hfsplus_readdir() method is capable to crash by calling
hfsplus_uni2asc():

[  667.121659][ T9805] ==================================================================
[  667.122651][ T9805] BUG: KASAN: slab-out-of-bounds in hfsplus_uni2asc+0x902/0xa10
[  667.123627][ T9805] Read of size 2 at addr ffff88802592f40c by task repro/9805
[  667.124578][ T9805]
[  667.124876][ T9805] CPU: 3 UID: 0 PID: 9805 Comm: repro Not tainted 6.16.0-rc3 #1 PREEMPT(full)
[  667.124886][ T9805] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[  667.124890][ T9805] Call Trace:
[  667.124893][ T9805]  <TASK>
[  667.124896][ T9805]  dump_stack_lvl+0x10e/0x1f0
[  667.124911][ T9805]  print_report+0xd0/0x660
[  667.124920][ T9805]  ? __virt_addr_valid+0x81/0x610
[  667.124928][ T9805]  ? __phys_addr+0xe8/0x180
[  667.124934][ T9805]  ? hfsplus_uni2asc+0x902/0xa10
[  667.124942][ T9805]  kasan_report+0xc6/0x100
[  667.124950][ T9805]  ? hfsplus_uni2asc+0x902/0xa10
[  667.124959][ T9805]  hfsplus_uni2asc+0x902/0xa10
[  667.124966][ T9805]  ? hfsplus_bnode_read+0x14b/0x360
[  667.124974][ T9805]  hfsplus_readdir+0x845/0xfc0
[  667.124984][ T9805]  ? __pfx_hfsplus_readdir+0x10/0x10
[  667.124994][ T9805]  ? stack_trace_save+0x8e/0xc0
[  667.125008][ T9805]  ? iterate_dir+0x18b/0xb20
[  667.125015][ T9805]  ? trace_lock_acquire+0x85/0xd0
[  667.125022][ T9805]  ? lock_acquire+0x30/0x80
[  667.125029][ T9805]  ? iterate_dir+0x18b/0xb20
[  667.125037][ T9805]  ? down_read_killable+0x1ed/0x4c0
[  667.125044][ T9805]  ? putname+0x154/0x1a0
[  667.125051][ T9805]  ? __pfx_down_read_killable+0x10/0x10
[  667.125058][ T9805]  ? apparmor_file_permission+0x239/0x3e0
[  667.125069][ T9805]  iterate_dir+0x296/0xb20
[  667.125076][ T9805]  __x64_sys_getdents64+0x13c/0x2c0
[  667.125084][ T9805]  ? __pfx___x64_sys_getdents64+0x10/0x10
[  667.125091][ T9805]  ? __x64_sys_openat+0x141/0x200
[  667.125126][ T9805]  ? __pfx_filldir64+0x10/0x10
[  667.125134][ T9805]  ? do_user_addr_fault+0x7fe/0x12f0
[  667.125143][ T9805]  do_syscall_64+0xc9/0x480
[  667.125151][ T9805]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  667.125158][ T9805] RIP: 0033:0x7fa8753b2fc9
[  667.125164][ T9805] Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 48
[  667.125172][ T9805] RSP: 002b:00007ffe96f8e0f8 EFLAGS: 00000217 ORIG_RAX: 00000000000000d9
[  667.125181][ T9805] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fa8753b2fc9
[  667.125185][ T9805] RDX: 0000000000000400 RSI: 00002000000063c0 RDI: 0000000000000004
[  667.125190][ T9805] RBP: 00007ffe96f8e110 R08: 00007ffe96f8e110 R09: 00007ffe96f8e110
[  667.125195][ T9805] R10: 0000000000000000 R11: 0000000000000217 R12: 0000556b1e3b4260
[  667.125199][ T9805] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[  667.125207][ T9805]  </TASK>
[  667.125210][ T9805]
[  667.145632][ T9805] Allocated by task 9805:
[  667.145991][ T9805]  kasan_save_stack+0x20/0x40
[  667.146352][ T9805]  kasan_save_track+0x14/0x30
[  667.146717][ T9805]  __kasan_kmalloc+0xaa/0xb0
[  667.147065][ T9805]  __kmalloc_noprof+0x205/0x550
[  667.147448][ T9805]  hfsplus_find_init+0x95/0x1f0
[  667.147813][ T9805]  hfsplus_readdir+0x220/0xfc0
[  667.148174][ T9805]  iterate_dir+0x296/0xb20
[  667.148549][ T9805]  __x64_sys_getdents64+0x13c/0x2c0
[  667.148937][ T9805]  do_syscall_64+0xc9/0x480
[  667.149291][ T9805]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  667.149809][ T9805]
[  667.150030][ T9805] The buggy address belongs to the object at ffff88802592f000
[  667.150030][ T9805]  which belongs to the cache kmalloc-2k of size 2048
[  667.151282][ T9805] The buggy address is located 0 bytes to the right of
[  667.151282][ T9805]  allocated 1036-byte region [ffff88802592f000, ffff88802592f40c)
[  667.1
---truncated---

Statement: This vulnerability does not require elevated user privileges to trigger, but does require a corrupted HFS+ filesystem where the `length` values in the `hfsplus_unistr` data structures are invalid. This corruption must exist on disk in the filesystem metadata.

Remediation: