[PATCH 2/3] erofs: use LZ4_decompress_safe() for full decoding

[Gao Xiang]

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 corrupted images and
it might have some speed gain as well although I didn't observe
much difference.

Cc: Lasse Collin <lasse.collin at tukaani.org>
Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
---
 fs/erofs/decompressor.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 5779a15c2cd6..c77cec4327fa 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -157,9 +157,14 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out)
 		}
 	}
 
-	ret = LZ4_decompress_safe_partial(src + inputmargin, out,
-					  inlen, rq->outputsize,
-					  rq->outputsize);
+	if (rq->partial_decoding)
+		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);
-- 
2.17.1