Commit af1038ab authored Feb 26, 2020 by Gao Xiang

erofs: use LZ4_decompress_safe() for full decoding

As Lasse pointed out, "EROFS uses LZ4_decompress_safe_partial
for both partial and full blocks. Thus when it is decoding a
full block, it doesn't know if the LZ4 decoder actually decoded
all the input. The real uncompressed size could be bigger than
the value stored in the file system metadata.

Using LZ4_decompress_safe instead of _safe_partial when
decompressing a full block would help to detect errors."

So it's reasonable to use _safe in case of potential corrupted
images and it might have some speed gain as well although
I didn't observe much difference.

Note that legacy compressor (< 5.3, no LZ4_0PADDING) could
encode extra data in a pcluster, which is excluded as well.

Cc: Lasse Collin <lasse.collin@tukaani.org>
Fixes: 0ffd71bc ("staging: erofs: introduce LZ4 decompression inplace")
[ Gao Xiang: v5.3+, I will manually backport this to stable later. ]
Link: https://lore.kernel.org/r/20200226081008.86348-2-gaoxiang25@huawei.com


Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>

parent 9d5a09c6

fs/erofs/decompressor.c

+9 −3

Original line number	Diff line number	Diff line
		@@ -157,9 +157,15 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req rq, u8 out)
		}
		}

		/* legacy format could compress extra data in a pcluster. */
		if (rq->partial_decoding \|\| !support_0padding)
		ret = LZ4_decompress_safe_partial(src + inputmargin, out,
		inlen, rq->outputsize,
		rq->outputsize);
		else
		ret = LZ4_decompress_safe(src + inputmargin, out,
		inlen, rq->outputsize);

		if (ret < 0) {
		erofs_err(rq->sb, "failed to decompress, in[%u, %u] out[%u]",
		inlen, inputmargin, rq->outputsize);

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