Re: [PATCH 1/4] fscrypt: Cap data units at the page size

[sashiko-bot@kernel.org]

> blk-crypto-fallback cannot handle a data unit larger than a page:
> it walks the bio one page-sized segment at a time, so a data unit
> that spans multiple pages never ends on a segment boundary and
> the bio fails with BLK_STS_INVAL after the I/O was already
> reported to userspace as successful, losing data.
> 
> Fix this in fscrypt_supported_v2_policy() by rejecting any v2 policy
> that explicitly specifies a data unit size larger than the page size.
> 
> A v1 policy always uses the block size as its data unit size,
> so fscrypt_supported_v1_policy() has to reject any v1 policy on
> a filesystem with a block size larger than the page size (e.g. ext4).
> 
> A v2 policy with no data unit size specified uses the block size too,
> but rejection is not necessary there: sub-block data units are
> supported, so it is enough to cap the data unit bits at PAGE_SHIFT in
> fscrypt_policy_v2_du_bits().
> 
> Note that a filesystem whose block size exceeds 4K then cannot be
> made compatible across page sizes (e.g. 4K and 64K); this can be
> avoided by explicitly specifying a data unit size of 4K or smaller.
> 
> Suggested-by: Eric Biggers <ebiggers@kernel.org>
> Link: https://lore.kernel.org/r/20261015185325.GG2170687@google.com
> Signed-off-by: Baokun Li <libaokun@linux.alibaba.com>

Sashiko has reviewed this patch and found no issues.

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