Messages in this thread | | | Subject | Re: [PATCH v4] erofs: support superblock checksum | From | Chao Yu <> | Date | Mon, 28 Oct 2019 20:36:00 +0800 |
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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 > > . >
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