[syzbot] [hfs?] KASAN: out-of-bounds Read in hfs_bnode_move

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 89be9a83ccf1 Linux 6.16-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17ac1b82580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8adfe52da0de2761
dashboard link: https://syzkaller.appspot.com/bug?extid=41ba9c82bce8d7101765
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1771ef22580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11f764f0580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-89be9a83.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a3f5f507f252/vmlinux-89be9a83.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a8f9b92c57a6/bzImage-89be9a83.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/f02d92e4771f/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+41ba9c...@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 64
==================================================================
BUG: KASAN: out-of-bounds in hfs_bnode_move+0xea/0x130 fs/hfs/bnode.c:143
Read of size 18446744073709486080 at addr ffff888000994400 by task syz.0.16/5547

CPU: 0 UID: 0 PID: 5547 Comm: syz.0.16 Not tainted 6.16.0-rc7-syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x230 mm/kasan/report.c:480
kasan_report+0x118/0x150 mm/kasan/report.c:593
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:189
__asan_memmove+0x29/0x70 mm/kasan/shadow.c:94
hfs_bnode_move+0xea/0x130 fs/hfs/bnode.c:143
hfs_brec_remove+0x467/0x550 fs/hfs/brec.c:222
hfs_cat_move+0x6fb/0x960 fs/hfs/catalog.c:364
hfs_rename+0x1dc/0x2d0 fs/hfs/dir.c:299
vfs_rename+0xb99/0xec0 fs/namei.c:5137
do_renameat2+0x878/0xc50 fs/namei.c:5286
__do_sys_rename fs/namei.c:5333 [inline]
__se_sys_rename fs/namei.c:5331 [inline]
__x64_sys_rename+0x82/0x90 fs/namei.c:5331
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f11db18e9a9
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:00007ffd56ec9fe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
RAX: ffffffffffffffda RBX: 00007f11db3b5fa0 RCX: 00007f11db18e9a9
RDX: 0000000000000000 RSI: 0000200000000780 RDI: 00002000000003c0
RBP: 00007f11db210d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f11db3b5fa0 R14: 00007f11db3b5fa0 R15: 0000000000000002
</TASK>

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x35 pfn:0x994
memcg:ffff888030a98000
anon flags: 0x7ff00000020908(uptodate|active|owner_2|swapbacked|node=0|zone=0|lastcpupid=0x7ff)
raw: 007ff00000020908 0000000000000000 dead000000000122 ffff888059a96cc1
raw: 0000000000000035 0000000000000000 00000001ffffffff ffff888030a98000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Movable, gfp_mask 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 5548, tgid 5548 (dhcpcd-run-hook), ts 123108746961, free_ts 121368908469
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1704
prep_new_page mm/page_alloc.c:1712 [inline]
get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3669
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4959
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2419
folio_alloc_mpol_noprof mm/mempolicy.c:2438 [inline]
vma_alloc_folio_noprof+0xe4/0x200 mm/mempolicy.c:2473
folio_prealloc+0x30/0x180 mm/memory.c:-1
wp_page_copy mm/memory.c:3569 [inline]
do_wp_page+0x1231/0x5800 mm/memory.c:4030
handle_pte_fault mm/memory.c:6085 [inline]
__handle_mm_fault+0x1144/0x5620 mm/memory.c:6212
handle_mm_fault+0x40a/0x8e0 mm/memory.c:6381
do_user_addr_fault+0xa81/0x1390 arch/x86/mm/fault.c:1336
handle_page_fault arch/x86/mm/fault.c:1476 [inline]
exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
page last free pid 5509 tgid 5509 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1248 [inline]
free_unref_folios+0xc66/0x14d0 mm/page_alloc.c:2763
folios_put_refs+0x559/0x640 mm/swap.c:992
free_pages_and_swap_cache+0x4be/0x520 mm/swap_state.c:267
__tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:397 [inline]
tlb_flush_mmu+0x3a0/0x680 mm/mmu_gather.c:404
tlb_finish_mmu+0xc3/0x1d0 mm/mmu_gather.c:497
exit_mmap+0x44c/0xb50 mm/mmap.c:1297
__mmput+0x118/0x420 kernel/fork.c:1121
exit_mm+0x1da/0x2c0 kernel/exit.c:581
do_exit+0x648/0x22e0 kernel/exit.c:952
do_group_exit+0x21c/0x2d0 kernel/exit.c:1105
__do_sys_exit_group kernel/exit.c:1116 [inline]
__se_sys_exit_group kernel/exit.c:1114 [inline]
__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1114
x64_sys_call+0x21ba/0x21c0 arch/x86/include/generated/asm/syscalls_64.h:232
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff888000994300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888000994380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888000994400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
^
ffff888000994480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888000994500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
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

[Viacheslav Dubeyko]

On Wed, 2025-07-23 at 10:18 -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>

Issue has been created:
https://github.com/hfs-linux-kernel/hfs-linux-kernel/issues/227

Thanks,
Slava.

[Lizhi Xu]

#syz test

diff --git a/fs/hfs/bnode.c b/fs/hfs/bnode.c
index cb823a8a6ba9..58c5cc7adf70 100644
--- a/fs/hfs/bnode.c
+++ b/fs/hfs/bnode.c
@@ -134,7 +134,7 @@ void hfs_bnode_move(struct hfs_bnode *node, int dst, int src, int len)
void *ptr;

hfs_dbg(BNODE_MOD, "movebytes: %u,%u,%u\n", dst, src, len);
- if (!len)
+ if (len <= 0)
return;
src += node->page_offset;
dst += node->page_offset;

[syzbot]

Hello,

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

Reported-by: syzbot+41ba9c...@syzkaller.appspotmail.com
Tested-by: syzbot+41ba9c...@syzkaller.appspotmail.com

Tested on:

commit: 25fae0b9 Merge tag 'drm-fixes-2025-07-24' of https://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12ae40a2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=859f36d9ccbeaa3e

dashboard link: https://syzkaller.appspot.com/bug?extid=41ba9c82bce8d7101765
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

patch: https://syzkaller.appspot.com/x/patch.diff?x=150160a2580000

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

[Edward Adam Davis]

#syz test

diff --git a/fs/hfs/brec.c b/fs/hfs/brec.c
index 896396554bcc..763b6209a198 100644
--- a/fs/hfs/brec.c
+++ b/fs/hfs/brec.c
@@ -208,7 +208,7 @@ int hfs_brec_remove(struct hfs_find_data *fd)
}
hfs_bnode_write_u16(node, offsetof(struct hfs_bnode_desc, num_recs), node->num_recs);

- if (rec_off == end_off)
+ if (rec_off <= end_off)
goto skip;
size = fd->keylength + fd->entrylength;

[syzbot]

Hello,

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

Reported-by: syzbot+41ba9c...@syzkaller.appspotmail.com
Tested-by: syzbot+41ba9c...@syzkaller.appspotmail.com

Tested on:

commit: 25fae0b9 Merge tag 'drm-fixes-2025-07-24' of https://g..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=170ae0a2580000

kernel config: https://syzkaller.appspot.com/x/.config?x=859f36d9ccbeaa3e
dashboard link: https://syzkaller.appspot.com/bug?extid=41ba9c82bce8d7101765
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

patch: https://syzkaller.appspot.com/x/patch.diff?x=152e3fd4580000

[Edward Adam Davis]

#syz test

diff --git a/fs/hfs/bfind.c b/fs/hfs/bfind.c
index ef9498a6e88a..1d6f2bbafa7a 100644
--- a/fs/hfs/bfind.c
+++ b/fs/hfs/bfind.c
@@ -133,6 +133,8 @@ int hfs_brec_find(struct hfs_find_data *fd)
goto invalid;
if (bnode->type != (--height ? HFS_NODE_INDEX : HFS_NODE_LEAF))
goto invalid;
+ if (!bnode->num_recs)
+ goto invalid;
bnode->parent = parent;

res = __hfs_brec_find(bnode, fd);

[syzbot]

Hello,

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

Reported-by: syzbot+41ba9c...@syzkaller.appspotmail.com
Tested-by: syzbot+41ba9c...@syzkaller.appspotmail.com

Tested on:

commit: 25fae0b9 Merge tag 'drm-fixes-2025-07-24' of https://g..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=127b30a2580000

kernel config: https://syzkaller.appspot.com/x/.config?x=859f36d9ccbeaa3e
dashboard link: https://syzkaller.appspot.com/bug?extid=41ba9c82bce8d7101765
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

patch: https://syzkaller.appspot.com/x/patch.diff?x=123a30a2580000

[Edward Adam Davis]

If the number of entries in the bnode is 0, the bnode is considered
invalid.

Reported-by: syzbot+41ba9c...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=41ba9c82bce8d7101765
Tested-by: syzbot+41ba9c...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
fs/hfs/bfind.c | 2 ++
1 file changed, 2 insertions(+)

--
2.43.0

[Viacheslav Dubeyko]

If b-tree node hasn't records, then it doesn't mean that it's invalid. Because,
if we go into invalid way, then we show the message that node is corrupted [1]:

invalid:
pr_err("inconsistency in B*Tree (%d,%d,%d,%u,%u)\n",
height, bnode->height, bnode->type, nidx, parent);
res = -EIO;

But it is not true because the node simply has no records. It could be invalid
if bnode->num_recs < 0.

Also, I've sent the patch [2] already. I believe it should fix the issue. Am I
wrong here?

Thanks,
Slava.

[1] https://elixir.bootlin.com/linux/v6.16-rc6/source/fs/hfs/bfind.c#L152
[2]
https://lore.kernel.org/linux-fsdevel/20250703214912...@dubeyko.com/

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 736a0516a16268995f4898eded49bfef077af709
Author: Viacheslav Dubeyko <sl...@dubeyko.com>
Date: Thu Jul 10 21:36:57 2025 +0000

hfs: fix general protection fault in hfs_find_init()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1519c634580000
start commit: 01a412d06bc5 Merge tag 'pull-ufs-fix' of git://git.kernel...
git tree: upstream

kernel config: https://syzkaller.appspot.com/x/.config?x=859f36d9ccbeaa3e
dashboard link: https://syzkaller.appspot.com/bug?extid=41ba9c82bce8d7101765

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15611b82580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=117cff22580000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: hfs: fix general protection fault in hfs_find_init()

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.