Re: [PATCH] hfs/hfsplus: fix slab-out-of-bounds in hfs_bnode_read_key

Attila Szasz
2025-03-27T19:15:41Z

hi, Attila here—the one who wrote the article and the PoC.

just for the record: this was a mistake then, and if one happens to
discover another impactful bug in a potentially orphaned filesystem or
another subsystem, it might EVEN get prioritized by upstream and stable
over /panic_on_warn/ stuff next time, right? or am I missing something?

On 3/24/25 17:17, Greg KH wrote:
> On Mon, Mar 24, 2025 at 07:14:07PM +0300, Cengiz Can wrote:
>> On 20-03-25 20:30:15, Salvatore Bonaccorso wrote:
>>> Hi
>>>
>> Hello Salvatore,
>>
>>> On Sat, Oct 19, 2024 at 10:13:03PM +0300, Vasiliy Kovalev wrote:
>>>> Syzbot reported an issue in hfs subsystem:
>>>>
>>>> BUG: KASAN: slab-out-of-bounds in memcpy_from_page include/linux/highmem.h:423 [inline]
>>>> BUG: KASAN: slab-out-of-bounds in hfs_bnode_read fs/hfs/bnode.c:35 [inline]
>>>> BUG: KASAN: slab-out-of-bounds in hfs_bnode_read_key+0x314/0x450 fs/hfs/bnode.c:70
>>>> Write of size 94 at addr ffff8880123cd100 by task syz-executor237/5102
>>>>
>>>> Call Trace:
>>>> <TASK>
>>>> __dump_stack lib/dump_stack.c:94 [inline]
>>>> dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>>>> print_address_description mm/kasan/report.c:377 [inline]
>>>> print_report+0x169/0x550 mm/kasan/report.c:488
>>>> kasan_report+0x143/0x180 mm/kasan/report.c:601
>>>> kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
>>>> __asan_memcpy+0x40/0x70 mm/kasan/shadow.c:106
>>>> memcpy_from_page include/linux/highmem.h:423 [inline]
>>>> hfs_bnode_read fs/hfs/bnode.c:35 [inline]
>>>> hfs_bnode_read_key+0x314/0x450 fs/hfs/bnode.c:70
>>>> hfs_brec_insert+0x7f3/0xbd0 fs/hfs/brec.c:159
>>>> hfs_cat_create+0x41d/0xa50 fs/hfs/catalog.c:118
>>>> hfs_mkdir+0x6c/0xe0 fs/hfs/dir.c:232
>>>> vfs_mkdir+0x2f9/0x4f0 fs/namei.c:4257
>>>> do_mkdirat+0x264/0x3a0 fs/namei.c:4280
>>>> __do_sys_mkdir fs/namei.c:4300 [inline]
>>>> __se_sys_mkdir fs/namei.c:4298 [inline]
>>>> __x64_sys_mkdir+0x6c/0x80 fs/namei.c:4298
>>>> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>>>> do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>>> RIP: 0033:0x7fbdd6057a99
>>>>
>>>> Add a check for key length in hfs_bnode_read_key to prevent
>>>> out-of-bounds memory access. If the key length is invalid, the
>>>> key buffer is cleared, improving stability and reliability.
>>>>
>>>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>>>> Reported-by:syzbot+5f3a973ed3dfb85a6683@syzkaller.appspotmail.com
>>>> Closes:https://syzkaller.appspot.com/bug?extid=5f3a973ed3dfb85a6683
>>>> Cc:stable@vger.kernel.org
>>>> Signed-off-by: Vasiliy Kovalev<kovalev@altlinux.org>
>>>> ---
>>>> fs/hfs/bnode.c | 6 ++++++
>>>> fs/hfsplus/bnode.c | 6 ++++++
>>>> 2 files changed, 12 insertions(+)
>>>>
>>>> diff --git a/fs/hfs/bnode.c b/fs/hfs/bnode.c
>>>> index 6add6ebfef8967..cb823a8a6ba960 100644
>>>> --- a/fs/hfs/bnode.c
>>>> +++ b/fs/hfs/bnode.c
>>>> @@ -67,6 +67,12 @@ void hfs_bnode_read_key(struct hfs_bnode *node, void *key, int off)
>>>> else
>>>> key_len = tree->max_key_len + 1;
>>>>
>>>> + if (key_len > sizeof(hfs_btree_key) || key_len < 1) {
>>>> + memset(key, 0, sizeof(hfs_btree_key));
>>>> + pr_err("hfs: Invalid key length: %d\n", key_len);
>>>> + return;
>>>> + }
>>>> +
>>>> hfs_bnode_read(node, key, off, key_len);
>>>> }
>> Simpler the better.
>>
>> Our fix was released back in February. (There are other issues in our attempt I
>> admit).
>>
>> https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy/commit/?id=2e8d8dffa2e0b5291522548309ec70428be7cf5a
>>
>> If someone can pick this submission, I will be happy to replace our version.
> any specific reason why you didn't submit this upstream? Or did that
> happen and it somehow not get picked up?
>
> And why assign a CVE for an issue that is in the mainline kernel, last I
> checked, Canonical was NOT allowed to do that.
>
> Please work to revoke that CVE and ask for one properly.
>
> thanks,
>
> greg k-h
>