From 4535b0a69314be835ef8c6d07df0403b254f3c9e Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Thu, 5 Mar 2015 11:20:06 +0000 Subject: [PATCH] dmg: prevent chunk buffer overflow (CVE-2014-0145) Both compressed and uncompressed I/O is buffered. dmg_open() calculates the maximum buffer size needed from the metadata in the image file. There is currently a buffer overflow since ->lengths[] is accounted against the maximum compressed buffer size but actually uses the uncompressed buffer: switch (s->types[chunk]) { case 1: /* copy */ ret = bdrv_pread(bs->file, s->offsets[chunk], s->uncompressed_chunk, s->lengths[chunk]); We must account against the maximum uncompressed buffer size for type=1 chunks. This patch fixes the maximum buffer size calculation to take into account the chunk type. It is critical that we update the correct maximum since there are two buffers ->compressed_chunk and ->uncompressed_chunk. Signed-off-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf Reviewed-by: Max Reitz Signed-off-by: Stefan Hajnoczi Signed-off-by: Stefano Stabellini --- block/dmg.c | 37 +++++++++++++++++++++++++++++++++---- 1 file changed, 33 insertions(+), 4 deletions(-) diff --git a/block/dmg.c b/block/dmg.c index 37902a434..dc3b50754 100644 --- a/block/dmg.c +++ b/block/dmg.c @@ -73,6 +73,37 @@ static off_t read_uint32(BlockDriverState *bs, int64_t offset) return be32_to_cpu(buffer); } +/* Increase max chunk sizes, if necessary. This function is used to calculate + * the buffer sizes needed for compressed/uncompressed chunk I/O. + */ +static void update_max_chunk_size(BDRVDMGState *s, uint32_t chunk, + uint32_t *max_compressed_size, + uint32_t *max_sectors_per_chunk) +{ + uint32_t compressed_size = 0; + uint32_t uncompressed_sectors = 0; + + switch (s->types[chunk]) { + case 0x80000005: /* zlib compressed */ + compressed_size = s->lengths[chunk]; + uncompressed_sectors = s->sectorcounts[chunk]; + break; + case 1: /* copy */ + uncompressed_sectors = (s->lengths[chunk] + 511) / 512; + break; + case 2: /* zero */ + uncompressed_sectors = s->sectorcounts[chunk]; + break; + } + + if (compressed_size > *max_compressed_size) { + *max_compressed_size = compressed_size; + } + if (uncompressed_sectors > *max_sectors_per_chunk) { + *max_sectors_per_chunk = uncompressed_sectors; + } +} + static int dmg_open(BlockDriverState *bs, int flags) { BDRVDMGState *s = bs->opaque; @@ -161,10 +192,8 @@ static int dmg_open(BlockDriverState *bs, int flags) s->lengths[i] = read_off(bs, offset); offset += 8; - if(s->lengths[i]>max_compressed_size) - max_compressed_size = s->lengths[i]; - if(s->sectorcounts[i]>max_sectors_per_chunk) - max_sectors_per_chunk = s->sectorcounts[i]; + update_max_chunk_size(s, i, &max_compressed_size, + &max_sectors_per_chunk); } s->n_chunks+=chunk_count; } -- 2.39.5