linux-kernel - Re: [PATCH] Revert "f2fs: avoid out-of-range memory access"

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Message-ID: <5c449273-5cf7-bcc6-a396-584b933833c1@huawei.com>
Date:   Tue, 6 Aug 2019 10:07:45 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>
Subject: Re: [PATCH] Revert "f2fs: avoid out-of-range memory access"

On 2019/8/6 9:28, Jaegeuk Kim wrote:
> On 08/06, Chao Yu wrote:
>> On 2019/8/6 8:42, Jaegeuk Kim wrote:
>>> On 08/02, Chao Yu wrote:
>>>> As Pavel Machek reported:
>>>>
>>>> "We normally use -EUCLEAN to signal filesystem corruption. Plus, it is
>>>> good idea to report it to the syslog and mark filesystem as "needing
>>>> fsck" if filesystem can do that."
>>>>
>>>> Still we need improve the original patch with:
>>>> - use unlikely keyword
>>>> - add message print
>>>> - return EUCLEAN
>>>>
>>>> However, after rethink this patch, I don't think we should add such
>>>> condition check here as below reasons:
>>>> - We have already checked the field in f2fs_sanity_check_ckpt(),
>>>> - If there is fs corrupt or security vulnerability, there is nothing
>>>> to guarantee the field is integrated after the check, unless we do
>>>> the check before each of its use, however no filesystem does that.
>>>> - We only have similar check for bitmap, which was added due to there
>>>> is bitmap corruption happened on f2fs' runtime in product.
>>>> - There are so many key fields in SB/CP/NAT did have such check
>>>> after f2fs_sanity_check_{sb,cp,..}.
>>>>
>>>> So I propose to revert this unneeded check.
>>>
>>> IIRC, this came from security vulnerability report which can access
>>
>> I don't think that's correct report, since we have checked validation of that
>> field during mount, if it can be ruined after that, any variables can't be trusted.
> 
> I assumed this was reproduced with a fuzzed image.

I expect f2fs_sanity_check_ckpt() should reject mounting such fuzzed image.

> I'll check it with Ocean.
> 
>>
>> Now we just check bitmaps at real-time, because we have encountered such bitmap
>> corruption in product.
>>
>> Thanks,
>>
>>> out-of-boundary memory region. Could you write another patch to address the
>>> above issues?
>>>
>>>>
>>>> This reverts commit 56f3ce675103e3fb9e631cfb4131fc768bc23e9a.
>>>>
>>>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>>>> ---
>>>>  fs/f2fs/segment.c | 5 -----
>>>>  1 file changed, 5 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>> index 9693fa4c8971..2eff9c008ae0 100644
>>>> --- a/fs/f2fs/segment.c
>>>> +++ b/fs/f2fs/segment.c
>>>> @@ -3492,11 +3492,6 @@ static int read_compacted_summaries(struct f2fs_sb_info *sbi)
>>>>  		seg_i = CURSEG_I(sbi, i);
>>>>  		segno = le32_to_cpu(ckpt->cur_data_segno[i]);
>>>>  		blk_off = le16_to_cpu(ckpt->cur_data_blkoff[i]);
>>>> -		if (blk_off > ENTRIES_IN_SUM) {
>>>> -			f2fs_bug_on(sbi, 1);
>>>> -			f2fs_put_page(page, 1);
>>>> -			return -EFAULT;
>>>> -		}
>>>>  		seg_i->next_segno = segno;
>>>>  		reset_curseg(sbi, i, 0);
>>>>  		seg_i->alloc_type = ckpt->alloc_type[i];
>>>> -- 
>>>> 2.18.0.rc1
>>> .
>>>
> .
>