cbfstool: If compression fails, warn and use the uncompressed data.

The LZMA compression algorithm, currently the only one available, will fail
if you ask it to write more data to the output than you've given it space for.
The code that calls into LZMA allocates an output buffer the same size as the
input, so if compression increases the size of the output the call will fail.
The caller(s) were written to assume that the call succeeded and check the
returned length to see if the size would have increased, but that will never
happen with LZMA.

Rather than try to rework the LZMA library to dynamically resize the output
buffer or try to guess what the maximal size the data could expand to is, this
change makes the caller simply print a warning and disable compression if the
call failed for some reason.

This may lead to images that are larger than necessary if compression fails
for some other reason and the user doesn't notice, but since compression
errors were ignored entirely until very recently that will hopefully not be
a problem in practice, and we should be guaranteed to at least produce a
correct image.

Original-Change-Id: I5f59529c2d48e9c4c2e011018b40ec336c4fcca8
Original-Signed-off-by: Gabe Black <gabeblack@google.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/187365
Original-Reviewed-by: David Hendricks <dhendrix@chromium.org>
Original-Tested-by: Gabe Black <gabeblack@chromium.org>
Original-Commit-Queue: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit b9f622a554d5fb9a9aff839c64e11acb27785f13)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>

Change-Id: I5f59529c2d48e9c4c2e011018b40ec336c4fcca8
Reviewed-on: http://review.coreboot.org/6958
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/util/cbfstool/cbfs-mkstage.c b/util/cbfstool/cbfs-mkstage.c
index 8c77ee5e65..4a2f4d8dee 100644
--- a/util/cbfstool/cbfs-mkstage.c
+++ b/util/cbfstool/cbfs-mkstage.c
@@ -155,12 +155,17 @@ int parse_elf_to_stage(const struct buffer *input, struct buffer *output,
 	 * to fill out the header. This seems backward but it works because
 	 * - the output header is a known size (not always true in many xdr's)
 	 * - we do need to know the compressed output size first
+	 * If compression fails or makes the data bigger, we'll warn about it
+	 * and use the original data.
 	 */
 	if (compress(buffer, data_end - data_start,
 		     (output->data + sizeof(struct cbfs_stage)),
-		     &outlen) < 0) {
-		free(buffer);
-		return -1;
+		     &outlen) < 0 || outlen > data_end - data_start) {
+		WARN("Compression failed or would make the data bigger "
+		     "- disabled.\n");
+		memcpy(output->data + sizeof(struct cbfs_stage),
+		       buffer, data_end - data_start);
+		algo = CBFS_COMPRESS_NONE;
 	}
 	free(buffer);