[wim] Do not attempt to decompress non-compressed chunks

A compressed WIM resource may contain individual chunks that are not compressed. The compressed and decompressed lengths are both calculable from the chunk table. The correct algorithm appears to be to treat the chunk as non-compressed if the "compressed" length is equal to the decompressed length. Signed-off-by: Michael Brown <mbrown@fensystems.co.uk>
ipxe · May 10, 2017 · 8ca9778 · 8ca9778
1 parent 0d8af67
commit 8ca9778
Showing 1 changed file with 12 additions and 6 deletions.
diff --git a/src/wim.c b/src/wim.c
@@ -149,7 +149,7 @@ static int wim_chunk ( struct vdisk_file *file, struct wim_header *header,
 	size_t offset;
 	size_t next_offset;
 	size_t len;
-	ssize_t expected_out_len;
+	size_t expected_out_len;
 	ssize_t out_len;
 	int rc;
 
@@ -167,11 +167,17 @@ static int wim_chunk ( struct vdisk_file *file, struct wim_header *header,
 	expected_out_len = ( ( chunk >= ( chunks - 1 ) ) ?
 			     ( resource->len % WIM_CHUNK_LEN ) : WIM_CHUNK_LEN);
 
-	/* Read compressed data into a temporary buffer and decompress it */
-	{
+	/* Read possibly-compressed data */
+	if ( len == expected_out_len ) {
+
+		/* Chunk did not compress; read raw data */
+		file->read ( file, buf->data, ( resource->offset + offset ),
+			     len );
+
+	} else {
 		uint8_t zbuf[len];
 
-		/* Read compressed data */
+		/* Read compressed data into a temporary buffer */
 		file->read ( file, zbuf, ( resource->offset + offset ), len );
 
 		/* Identify decompressor */
@@ -190,8 +196,8 @@ static int wim_chunk ( struct vdisk_file *file, struct wim_header *header,
 		out_len = decompress ( zbuf, len, NULL );
 		if ( out_len < 0 )
 			return out_len;
-		if ( out_len != expected_out_len ) {
-			DBG ( "Unexpected output length %#lx (expected %#lx)\n",
+		if ( ( ( size_t ) out_len ) != expected_out_len ) {
+			DBG ( "Unexpected output length %#lx (expected %#zx)\n",
 			      out_len, expected_out_len );
 			return -1;
 		}