From: Chao Yu <yuchao0@huawei.com>
To: Gao Xiang <gaoxiang25@huawei.com>
Cc: Gao Xiang <xiang@kernel.org>,
linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] erofs: support superblock checksum
Date: Mon, 28 Oct 2019 20:36:00 +0800 [thread overview]
Message-ID: <df7d7427-e7ca-5135-5db2-640eda30d253@huawei.com> (raw)
In-Reply-To: <20191023084536.GA16289@architecture4>
On 2019/10/23 16:45, Gao Xiang wrote:
> Hi Chao,
>
> On Wed, Oct 23, 2019 at 04:15:29PM +0800, Chao Yu wrote:
>> Hi, Xiang, Pratik,
>>
>> On 2019/10/23 12:05, Gao Xiang wrote:
>
> <snip>
>
>>> }
>>>
>>> +static int erofs_superblock_csum_verify(struct super_block *sb, void *sbdata)
>>> +{
>>> + struct erofs_super_block *dsb;
>>> + u32 expected_crc, nblocks, crc;
>>> + void *kaddr;
>>> + struct page *page;
>>> + int i;
>>> +
>>> + dsb = kmemdup(sbdata + EROFS_SUPER_OFFSET,
>>> + EROFS_BLKSIZ - EROFS_SUPER_OFFSET, GFP_KERNEL);
>>> + if (!dsb)
>>> + return -ENOMEM;
>>> +
>>> + expected_crc = le32_to_cpu(dsb->checksum);
>>> + nblocks = le32_to_cpu(dsb->chksum_blocks);
>>
>> Now, we try to use nblocks's value before checking its validation, I guess fuzz
>> test can easily make the value extreme larger, result in checking latter blocks
>> unnecessarily.
>>
>> IMO, we'd better
>> 1. check validation of superblock to make sure all fields in sb are valid
>> 2. use .nblocks to count and check payload blocks following sb
>
> That is quite a good point. :-)
>
> My first thought is to check the following payloads of sb (e.g, some per-fs
> metadata should be checked at mount time together. or for small images, check
> the whole image at the mount time) as well since if we introduce a new feature
> to some kernel version, forward compatibility needs to be considered. So it's
> better to make proper scalability, for this case, we have some choices:
> 1) limit `chksum_blocks' upbound at runtime (e.g. refuse >= 65536 blocks,
> totally 256M.)
> 2) just get rid of the whole `chksum_blocks' mess and checksum the first 4k
> at all, don't consider any latter scalability.
Xiang, sorry for later reply...
I prefer method 2), let's enable chksum feature only on superblock first,
chksum_blocks feature can be added later.
Thanks,
>
> Some perferred idea about this? I plan to release erofs-utils v1.0 tomorrow
> and hold up this feature for the next erofs-utils release, but I think we can
> get it ready for v5.5 since it is not quite complex feature...
>
> Thanks,
> Gao Xiang
>
> .
>
next prev parent reply other threads:[~2019-10-28 12:36 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-22 18:06 [PATCH-v3] erofs: code for verifying superblock checksum of an erofs image Pratik Shinde
2019-10-23 4:05 ` [PATCH v4] erofs: support superblock checksum Gao Xiang
2019-10-23 8:15 ` Chao Yu
2019-10-23 8:45 ` Gao Xiang
2019-10-28 12:36 ` Chao Yu [this message]
2019-10-28 13:44 ` Gao Xiang
2019-10-28 14:32 ` [PATCH v5] " Gao Xiang
2019-10-30 2:33 ` Chao Yu
2019-10-30 2:56 ` Gao Xiang
2019-10-30 5:08 ` [PATCH v6] " Gao Xiang
2019-11-04 2:49 ` [PATCH v7] " Gao Xiang
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