linux-kernel - Re: [PATCH v2] f2fs: fix to disallow getting inner inode via f2fs

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Date:   Thu, 8 Sep 2022 12:04:20 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <chao.yu@...o.com>
Subject: Re: [PATCH v2] f2fs: fix to disallow getting inner inode via
 f2fs_iget()

On 2022/9/8 10:19, Jaegeuk Kim wrote:
> On 09/08, Chao Yu wrote:
>> On 2022/9/8 10:02, Jaegeuk Kim wrote:
>>> On 08/31, Chao Yu wrote:
>>>> From: Chao Yu <chao.yu@...o.com>
>>>>
>>>> Introduce f2fs_iget_inner() for f2fs_fill_super() to get inner inode:
>>>> meta inode, node inode or compressed inode, and add f2fs_check_nid_range()
>>>> in f2fs_iget() to avoid getting inner inode from external interfaces.
>>>
>>> So, we don't want to check the range of inner inode numbers? What'd be the
>>> way to check it's okay?
>>
>> For node_ino, meta_ino, root_ino, we have checked them in sanity_check_raw_super()
>> as below:
>>
>> 	/* check reserved ino info */
>> 	if (le32_to_cpu(raw_super->node_ino) != 1 ||
>> 		le32_to_cpu(raw_super->meta_ino) != 2 ||
>> 		le32_to_cpu(raw_super->root_ino) != 3) {
>> 		f2fs_info(sbi, "Invalid Fs Meta Ino: node(%u) meta(%u) root(%u)",
>> 			  le32_to_cpu(raw_super->node_ino),
>> 			  le32_to_cpu(raw_super->meta_ino),
>> 			  le32_to_cpu(raw_super->root_ino));
>> 		return -EFSCORRUPTED;
>> 	}
>>
>> compressed_ino should always be NM_I(sbi)->max_nid, it can be checked in
>> f2fs_init_compress_inode()?
> 
> Hmm, I'm not sure whether we really need this patch, since it'd look better
> to handle all the iget with single f2fs_iget?

Well, the main concern is previously f2fs_iget() won't check validation for inner
inode due to it will skip do_read_inode() - f2fs_check_nid_range(), so that in a
fuzzed image, caller may pass inner ino into f2fs_iget(), result in incorrect use
of inner inode. So I add f2fs_check_nid_range() in prior to f2fs_iget_inner() in
f2fs_iget() as below to detect and avoid this case.

>>>> +struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
>>>> +{
>>>> +	int ret;
>>>> +
>>>> +	ret = f2fs_check_nid_range(F2FS_SB(sb), ino);
>>>> +	if (ret)
>>>> +		return ERR_PTR(ret);
>>>> +
>>>> +	return f2fs_iget_inner(sb, ino);