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Subject: Re: [PATCH 4.19 077/113] f2fs: avoid out-of-range memory access
To:     Pavel Machek <pavel@denx.de>, <pavel@ucw.cz>
CC:     <linux-kernel@vger.kernel.org>, Ocean Chen <oceanchen@google.com>,
        "Jaegeuk Kim" <jaegeuk@kernel.org>, Sasha Levin <sashal@kernel.org>
References: <20190729190655.455345569@linuxfoundation.org>
 <20190729190714.022413119@linuxfoundation.org> <20190731191115.GB4630@amd>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <15df49ee-0644-39a8-4c76-ed670f62fd62@huawei.com>
Date:   Thu, 1 Aug 2019 09:19:40 +0800
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On 2019/8/1 3:11, Pavel Machek wrote:
> Hi!
> 
>> [ Upstream commit 56f3ce675103e3fb9e631cfb4131fc768bc23e9a ]
>>
>> blkoff_off might over 512 due to fs corrupt or security
>> vulnerability. That should be checked before being using.
>>
>> Use ENTRIES_IN_SUM to protect invalid value in cur_data_blkoff.
>>
>> Signed-off-by: Ocean Chen <oceanchen@google.com>
>> Reviewed-by: Chao Yu <yuchao0@huawei.com>
>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>> Signed-off-by: Sasha Levin <sashal@kernel.org>
>> ---
>>  fs/f2fs/segment.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index 8fc3edb6760c..92f72bb5aff4 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -3261,6 +3261,11 @@ 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;
> 
> 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.

Thanks for pointing out this, I missed that restriction during review, since at
that time, my focus is on how that case happen...

Look at this again, I think we also need to add unlikely() keyword hint to
compiler to indicate this should never happen.

Thanks,

> 
> Thanks,
> 									Pavel
>