[syzbot] [hfs?] KMSAN: uninit-value in hfsplus_strcasecmp (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 603c05a1639f Merge tag 'nfs-for-6.19-2' of git://git.linux..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=178b339a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=46b5f80a6e7aaa5c
dashboard link: https://syzkaller.appspot.com/bug?extid=d80abb5b890d39261e72
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=157be39a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12625a3a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f5064e5f9c76/disk-603c05a1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c466bcf334e3/vmlinux-603c05a1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4e1318b36fb1/bzImage-603c05a1.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/a0364f040b52/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d80abb...@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 1024
=====================================================
BUG: KMSAN: uninit-value in case_fold fs/hfsplus/unicode.c:26 [inline]
BUG: KMSAN: uninit-value in hfsplus_strcasecmp+0x63a/0x980 fs/hfsplus/unicode.c:67
case_fold fs/hfsplus/unicode.c:26 [inline]
hfsplus_strcasecmp+0x63a/0x980 fs/hfsplus/unicode.c:67
hfsplus_cat_case_cmp_key+0xb9/0x190 fs/hfsplus/catalog.c:26
hfs_find_rec_by_key+0xae/0x240 fs/hfsplus/bfind.c:89
__hfsplus_brec_find+0x274/0x840 fs/hfsplus/bfind.c:124
hfsplus_brec_find+0x4ec/0xa10 fs/hfsplus/bfind.c:190
hfsplus_find_cat+0x3b0/0x4f0 fs/hfsplus/catalog.c:220
hfsplus_iget+0x815/0xc30 fs/hfsplus/super.c:96
hfsplus_fill_super+0x1550/0x2580 fs/hfsplus/super.c:548
get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1691
get_tree_bdev+0x38/0x50 fs/super.c:1714
hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:680
vfs_get_tree+0xb3/0x5c0 fs/super.c:1751
fc_mount fs/namespace.c:1199 [inline]
do_new_mount_fc fs/namespace.c:3636 [inline]
do_new_mount+0x879/0x1700 fs/namespace.c:3712
path_mount+0x749/0x1fb0 fs/namespace.c:4022
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount+0x6f7/0x7e0 fs/namespace.c:4201
__x64_sys_mount+0xe4/0x150 fs/namespace.c:4201
x64_sys_call+0x38cb/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd3/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
hfsplus_cat_build_key_uni fs/hfsplus/catalog.c:77 [inline]
hfsplus_find_cat+0x356/0x4f0 fs/hfsplus/catalog.c:217
hfsplus_iget+0x815/0xc30 fs/hfsplus/super.c:96
hfsplus_fill_super+0x1550/0x2580 fs/hfsplus/super.c:548
get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1691
get_tree_bdev+0x38/0x50 fs/super.c:1714
hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:680
vfs_get_tree+0xb3/0x5c0 fs/super.c:1751
fc_mount fs/namespace.c:1199 [inline]
do_new_mount_fc fs/namespace.c:3636 [inline]
do_new_mount+0x879/0x1700 fs/namespace.c:3712
path_mount+0x749/0x1fb0 fs/namespace.c:4022
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount+0x6f7/0x7e0 fs/namespace.c:4201
__x64_sys_mount+0xe4/0x150 fs/namespace.c:4201
x64_sys_call+0x38cb/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd3/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable tmp created at:
hfsplus_find_cat+0x43/0x4f0 fs/hfsplus/catalog.c:197
hfsplus_iget+0x815/0xc30 fs/hfsplus/super.c:96

CPU: 1 UID: 0 PID: 6037 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(none)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
=====================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: [PATCH] hfsplus: fix uninit-value in hfsplus_strcasecmp
Author: karti...@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Syzbot reported a KMSAN uninit-value issue in hfsplus_strcasecmp() during
filesystem mount operations. The root cause is that hfsplus_find_cat()
declares a local hfsplus_cat_entry variable without initialization before
passing it to hfs_brec_read().

If hfs_brec_read() doesn't completely fill the entire structure (e.g., when
the on-disk data is shorter than sizeof(hfsplus_cat_entry)), the padding
bytes in tmp.thread.nodeName remain uninitialized. These uninitialized
bytes are then copied by hfsplus_cat_build_key_uni() into the search key,
and subsequently accessed by hfsplus_strcasecmp() during catalog lookups,
triggering the KMSAN warning.

Fix this by zeroing the tmp variable before use to ensure all padding
bytes are initialized.

Reported-by: syzbot+d80abb...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d80abb5b890d39261e72
Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---
fs/hfsplus/catalog.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/fs/hfsplus/catalog.c b/fs/hfsplus/catalog.c
index 02c1eee4a4b8..9c75d1736427 100644
--- a/fs/hfsplus/catalog.c
+++ b/fs/hfsplus/catalog.c
@@ -199,6 +199,7 @@ int hfsplus_find_cat(struct super_block *sb, u32 cnid,
u16 type;

hfsplus_cat_build_key_with_cnid(sb, fd->search_key, cnid);
+ memset(&tmp, 0, sizeof(tmp));
err = hfs_brec_read(fd, &tmp, sizeof(hfsplus_cat_entry));
if (err)
return err;
--
2.43.0

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+d80abb...@syzkaller.appspotmail.com
Tested-by: syzbot+d80abb...@syzkaller.appspotmail.com

Tested on:

commit: 24d479d2 Linux 6.19-rc6
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13b44d22580000

kernel config: https://syzkaller.appspot.com/x/.config?x=46b5f80a6e7aaa5c
dashboard link: https://syzkaller.appspot.com/bug?extid=d80abb5b890d39261e72
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=16444d22580000

Note: testing is done by a robot and is best-effort only.