From f0dce23475b5af5da6b17b97c1765271307734b6 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Wed, 26 Mar 2014 13:06:00 +0100 Subject: 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 --- block/dmg.c | 39 +++++++++++++++++++++++++++++++++------ 1 file changed, 33 insertions(+), 6 deletions(-) (limited to 'block') diff --git a/block/dmg.c b/block/dmg.c index be0ee33..856402e 100644 --- a/block/dmg.c +++ b/block/dmg.c @@ -100,6 +100,37 @@ static int read_uint32(BlockDriverState *bs, int64_t offset, uint32_t *result) return 0; } +/* 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, QDict *options, int flags, Error **errp) { @@ -245,12 +276,8 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags, goto fail; } - 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; } -- cgit v1.1