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Subject: Re: [PATCH] hfs: Fix OOB Write in hfs_asc2mac
From:   Viacheslav Dubeyko <slava@dubeyko.com>
In-Reply-To: <2ca8a20b-047d-bae1-5a01-0892be4d7e7d@huawei.com>
Date:   Thu, 1 Dec 2022 15:09:22 -0800
Cc:     zippel@linux-m68k.org, akpm@osdl.org,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, sunnanyong@huawei.com,
        wangkefeng.wang@huawei.com,
        syzbot+dc3b1cf9111ab5fe98e7@syzkaller.appspotmail.com
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Message-Id: <7E14DFDD-CA11-46A7-8140-C4A0F9AD069D@dubeyko.com>
References: <20221126043612.853428-1-zhangpeng362@huawei.com>
 <9F97B7A6-9E20-4D70-BA79-8301D80DF9DB@dubeyko.com>
 <8e298cc0-27b9-a61a-48cc-64a9186048c8@huawei.com>
 <481BF13E-8CEA-48B4-A29B-0BDE4CAABAF9@dubeyko.com>
 <2ca8a20b-047d-bae1-5a01-0892be4d7e7d@huawei.com>
To:     "zhangpeng (AS)" <zhangpeng362@huawei.com>
Precedence: bulk


> On Nov 30, 2022, at 5:53 PM, zhangpeng (AS) <zhangpeng362@huawei.com> =
wrote:
>=20
>=20
> On 2022/11/30 3:08, Viacheslav Dubeyko wrote:
>>> On Nov 28, 2022, at 6:23 PM, zhangpeng (AS) =
<zhangpeng362@huawei.com> wrote:
>>>=20
>>> On 2022/11/29 3:29, Viacheslav Dubeyko wrote:
>>>>> On Nov 25, 2022, at 8:36 PM, Peng Zhang <zhangpeng362@huawei.com> =
wrote:
>>>>>=20
>>>>> From: ZhangPeng <zhangpeng362@huawei.com>
>>>>>=20
>>>>> Syzbot reported a OOB Write bug:
>>>>>=20
>>>>> loop0: detected capacity change from 0 to 64
>>>>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>>> BUG: KASAN: slab-out-of-bounds in hfs_asc2mac+0x467/0x9a0
>>>>> fs/hfs/trans.c:133
>>>>> Write of size 1 at addr ffff88801848314e by task =
syz-executor391/3632
>>>>>=20
>>>>> Call Trace:
>>>>> <TASK>
>>>>> __dump_stack lib/dump_stack.c:88 [inline]
>>>>> dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
>>>>> print_address_description+0x74/0x340 mm/kasan/report.c:284
>>>>> print_report+0x107/0x1f0 mm/kasan/report.c:395
>>>>> kasan_report+0xcd/0x100 mm/kasan/report.c:495
>>>>> hfs_asc2mac+0x467/0x9a0 fs/hfs/trans.c:133
>>>>> hfs_cat_build_key+0x92/0x170 fs/hfs/catalog.c:28
>>>>> hfs_lookup+0x1ab/0x2c0 fs/hfs/dir.c:31
>>>>> lookup_open fs/namei.c:3391 [inline]
>>>>> open_last_lookups fs/namei.c:3481 [inline]
>>>>> path_openat+0x10e6/0x2df0 fs/namei.c:3710
>>>>> do_filp_open+0x264/0x4f0 fs/namei.c:3740
>>>>>=20
>>>>> If in->len is much larger than HFS_NAMELEN(31) which is the =
maximum
>>>>> length of an HFS filename, a OOB Write could occur in =
hfs_asc2mac(). In
>>>>> that case, when the dst reaches the boundary, the srclen is still
>>>>> greater than 0, which causes a OOB Write.
>>>>> Fix this by adding a Check on dstlen before Writing to dst =
address.
>>>>>=20
>>>>> Fixes: 328b92278650 ("[PATCH] hfs: NLS support")
>>>>> Reported-by: syzbot+dc3b1cf9111ab5fe98e7@syzkaller.appspotmail.com
>>>>> Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
>>>>> ---
>>>>> fs/hfs/trans.c | 2 ++
>>>>> 1 file changed, 2 insertions(+)
>>>>>=20
>>>>> diff --git a/fs/hfs/trans.c b/fs/hfs/trans.c
>>>>> index 39f5e343bf4d..886158db07b3 100644
>>>>> --- a/fs/hfs/trans.c
>>>>> +++ b/fs/hfs/trans.c
>>>>> @@ -130,6 +130,8 @@ void hfs_asc2mac(struct super_block *sb, =
struct hfs_name *out, const struct qstr
>>>>> 				dst +=3D size;
>>>>> 				dstlen -=3D size;
>>>>> 			} else {
>>>>> +				if (dstlen =3D=3D 0)
>>>>> +					goto out;
>>>> Maybe, it makes sense to use dstlen instead of srclen in while()?
>>>>=20
>>>> We have now:
>>>>=20
>>>> while (srclen > 0) {
>>>>    <skipped>
>>>> } else {
>>>>    <skipped>
>>>> }
>>>>=20
>>>> We can use instead:
>>>>=20
>>>> while (dstlen > 0) {
>>>>    <skipped>
>>>> } else {
>>>>    <skipped>
>>>> }
>>>>=20
>>>> Will it fix the issue?
>>>>=20
>>>> Thanks,
>>>> Slava.
>>> Thank you for your help.
>>>=20
>>> After testing, it fix the issue.
>>> Would it be better to add dstlen > 0 instead of replacing srclen > 0 =
with dstlen > 0?
>>> Because there may be dstlen > 0 and srclen <=3D 0.
>>>=20
>>> we can use:
>>>=20
>>> while (srclen > 0 && dstlen > 0) {
>>>   <skipped>
>>> } else {
>>>   <skipped>
>>> }
>>>=20
>> Looks good to me.
>=20
> Can I put you down as a Reviewed-by or Suggested-by?

Sure. I hope to see the second version of the patch.

Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>

Thanks,
Slava.

>=20
> Thanks,
> Zhang Peng
>=20
>> Thanks,
>> Slava.
>>=20
>>> Thanks,
>>> Zhang Peng
>>>=20
>>>>> 				*dst++ =3D ch > 0xff ? '?' : ch;
>>>>> 				dstlen--;
>>>>> 			}
>>>>> --=20
>>>>> 2.25.1