Re: [PATCH v2 12/15] lib/lz4: widen LZ4_DECOMPRESS_INPLACE_MARGIN for the fast decode loop

[sashiko-bot@kernel.org]

> erofs decompresses a pcluster in place when the slack after the output
> is at least LZ4_DECOMPRESS_INPLACE_MARGIN(compressed size), upstream's
> (compressedSize >> 8) + 32.
> 
> That holds for the fork, which overshoots its output by at most 8
> bytes. Upstream's LZ4_FAST_DEC_LOOP, which the next patch brings in for
> x86 and arm64, copies in 32-byte steps and can overwrite input it has
> not read yet: of 172410 valid streams laid out as erofs does at exactly
> that margin, 3660 fail to decode, none with the fork. The worst needs
> (compressedSize >> 8) + 33. Images mkfs.erofs built did not hit this,
> but nothing in the format rules it out.
> 
> Use (compressedSize >> 8) + (compressedSize >> 15) + 36, which takes a
> 4K pcluster's margin from 48 to 52 bytes. Upstream's lz4.h defines the
> macro too, so undefine it first.
> 
> Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261106-lz4-vendor-upstream-v2-0-ee04c3f0d7dc@samsung.com?part=12