Forwarded: Private message regarding: [syzbot] [hfs?] kernel BUG in may_open (3)

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Subject: Private message regarding: [syzbot] [hfs?] kernel BUG in may_open (3)
Author: kapoorarnav43@gmail.com

#syz test
From: Arnav Kapoor <kapoorarnav43@gmail.com>
Date: Sun, 12 Jan 2026 14:36:00 +0000
Subject: [PATCH] hfsplus: ensure valid file mode in hfsplus_get_perms

Syzbot reported a kernel BUG in may_open() triggered by:
VFS_BUG_ON_INODE(!IS_ANON_FILE(inode), inode)

This occurs when an inode's i_mode doesn't match any standard file type
(S_IFREG, S_IFDIR, S_IFLNK, S_IFBLK, S_IFCHR, S_IFIFO, S_IFSOCK). The
crash happens when opening a file on a corrupted HFS+ filesystem where
the on-disk permissions structure has only file type bits set without
any permission bits.

In hfsplus_get_perms(), for directories, the code properly masks and
rebuilds the mode:
mode = (mode & S_IALLUGO) | S_IFDIR

However, for files with non-zero mode from disk, it directly assigns
the validated mode without ensuring permission bits are present. If
the on-disk mode is something like S_IFREG (0x8000) with no permission
bits, the inode ends up with i_mode lacking rwx bits entirely.

While such a mode passes the S_IFMT validation in the switch statement,
it creates an inode that can't be properly opened since it has no
access permissions.

Fix this by adding a check in the file path: if mode is non-zero and
valid but lacks any permission/attribute bits (S_IALLUGO mask), add
default read/write permissions like we do for the mode==0 case.

This ensures inodes always have sensible permission bits even when
reading from corrupted filesystems.

Reported-by: syzbot+f98189ed18c1f5f32e00@syzkaller.appspotmail.com
Tested-by: syzbot+f98189ed18c1f5f32e00@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=f98189ed18c1f5f32e00
Signed-off-by: Arnav Kapoor <kapoorarnav43@gmail.com>
---
fs/hfsplus/inode.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/hfsplus/inode.c b/fs/hfsplus/inode.c
index 000000000000..111111111111 100644
--- a/fs/hfsplus/inode.c
+++ b/fs/hfsplus/inode.c
@@ -214,10 +214,18 @@ static int hfsplus_get_perms(struct inode *inode,
inode->i_gid = sbi->gid;
if (dir) {
+ /* For directories, strip file type bits and rebuild */
mode = mode ? (mode & S_IALLUGO) : (S_IRWXUGO & ~(sbi->umask));
mode |= S_IFDIR;
- } else if (!mode)
+ } else if (!mode) {
+ /* For files with no mode, use default */
mode = S_IFREG | ((S_IRUGO|S_IWUGO) & ~(sbi->umask));
+ } else {
+ /* For files with mode, ensure we have permission bits */
+ if (!(mode & S_IALLUGO))
+ mode |= (S_IRUGO|S_IWUGO) & ~(sbi->umask);
+ }
+
inode->i_mode = mode;
HFSPLUS_I(inode)->userflags = perms->userflags;
-- 
2.43.0




On Monday, 12 January 2026 at 14:21:35 UTC+5:30 syzbot wrote:

Hello, 

syzbot found the following issue on: 

HEAD commit: b6151c4e60e5 Merge tag 'erofs-for-6.19-rc5-fixes' of git:/.. 
git tree: upstream 
console output: https://syzkaller.appspot.com/x/log.txt?x=15d45922580000 
kernel config: https://syzkaller.appspot.com/x/.config?x=7b058fb1d7dbe6b1 
dashboard link: https://syzkaller.appspot.com/bug?extid=f98189ed18c1f5f32e00 
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=14a7d19a580000 
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16a2f19a580000 

Downloadable assets: 
disk image: 
https://storage.googleapis.com/syzbot-assets/6eb5179ada01/disk-b6151c4e.raw.xz 
vmlinux: 
https://storage.googleapis.com/syzbot-assets/bc48d1a68ed0/vmlinux-b6151c4e.xz 
kernel image: 
https://storage.googleapis.com/syzbot-assets/061d4fb696a7/bzImage-b6151c4e.xz 
mounted in repro: 
https://storage.googleapis.com/syzbot-assets/df739de73585/mount_0.gz 

IMPORTANT: if you fix the issue, please add the following tag to the 
commit: 
Reported-by: syzbot+f98189...@syzkaller.appspotmail.com 

loop0: detected capacity change from 0 to 1024 
VFS_BUG_ON_INODE(!IS_ANON_FILE(inode)) encountered for inode 
ffff8880384b01e0 
fs hfsplus mode 0 opflags 0x4 flags 0x0 state 0x70 count 2 
------------[ cut here ]------------ 
kernel BUG at fs/namei.c:4210! 
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI 
CPU: 1 UID: 0 PID: 6062 Comm: syz.0.17 Not tainted syzkaller #0 
PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS 
Google 10/25/2025 
RIP: 0010:may_open+0x4b1/0x4c0 fs/namei.c:4210 
Code: 38 c1 0f 8c 1e fd ff ff 4c 89 e7 e8 c9 ec ef ff e9 11 fd ff ff e8 df 
b3 8d ff 4c 89 f7 48 c7 c6 80 53 f9 8a e8 10 eb f5 fe 90 <0f> 0b 66 66 66 
66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 
RSP: 0018:ffffc90003ba78e0 EFLAGS: 00010282 
RAX: 0000000000000088 RBX: dffffc0000000000 RCX: b41eda36b1e3ff00 
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 
RBP: 0000000000008241 R08: 0000000000000000 R09: 0000000000000000 
R10: dffffc0000000000 R11: fffff52000774ec1 R12: 0000000000000000 
R13: ffffffff8d709d80 R14: ffff8880384b01e0 R15: 0000000000000002 
FS: 000055557d7cd500(0000) GS:ffff888126def000(0000) knlGS:0000000000000000 
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 
CR2: 00007f01916a5890 CR3: 0000000040598000 CR4: 00000000003526f0 
Call Trace: 
<TASK> 
do_open fs/namei.c:4635 [inline] 
path_openat+0x32a8/0x3df0 fs/namei.c:4796 
do_filp_open+0x1fa/0x410 fs/namei.c:4823 
do_sys_openat2+0x121/0x200 fs/open.c:1430 
do_sys_open fs/open.c:1436 [inline] 
__do_sys_creat fs/open.c:1514 [inline] 
__se_sys_creat fs/open.c:1508 [inline] 
__x64_sys_creat+0x8f/0xc0 fs/open.c:1508 
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] 
do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94 
entry_SYSCALL_64_after_hwframe+0x77/0x7f 
RIP: 0033:0x7f739c0cf749 
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 
RSP: 002b:00007ffd4aa21ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000055 
RAX: ffffffffffffffda RBX: 00007f739c325fa0 RCX: 00007f739c0cf749 
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000200000000140 
RBP: 00007f739c153f91 R08: 0000000000000000 R09: 0000000000000000 
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 
R13: 00007f739c325fa0 R14: 00007f739c325fa0 R15: 0000000000000002 
</TASK> 
Modules linked in: 
---[ end trace 0000000000000000 ]--- 
RIP: 0010:may_open+0x4b1/0x4c0 fs/namei.c:4210 
Code: 38 c1 0f 8c 1e fd ff ff 4c 89 e7 e8 c9 ec ef ff e9 11 fd ff ff e8 df 
b3 8d ff 4c 89 f7 48 c7 c6 80 53 f9 8a e8 10 eb f5 fe 90 <0f> 0b 66 66 66 
66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 
RSP: 0018:ffffc90003ba78e0 EFLAGS: 00010282 
RAX: 0000000000000088 RBX: dffffc0000000000 RCX: b41eda36b1e3ff00 
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 
RBP: 0000000000008241 R08: 0000000000000000 R09: 0000000000000000 
R10: dffffc0000000000 R11: fffff52000774ec1 R12: 0000000000000000 
R13: ffffffff8d709d80 R14: ffff8880384b01e0 R15: 0000000000000002 
FS: 000055557d7cd500(0000) GS:ffff888126def000(0000) knlGS:0000000000000000 
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 
CR2: 00007f01916a5890 CR3: 0000000040598000 CR4: 00000000003526f0 


--- 
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