Commit message: block/cloop: validate block_size header field (CVE-2014-0144)

Avoid unbounded s->uncompressed_block memory allocation by checking that
the block_size header field has a reasonable value.  Also enforce the
assumption that the value is a non-zero multiple of 512.

These constraints conform to cloop 2.639's code so we accept existing
image files.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
CVE: CVE-2014-0144
CWE: CWE-20
Vulnerability description: QEMU before 2.0.0 block drivers for CLOOP, QCOW2 version 2 and various other image formats are vulnerable to potential memory corruptions, integer/buffer overflows or crash caused by missing input validations which could allow a remote user to execute arbitrary code on the host with the privileges of the QEMU process.

Project: qemu
File: cloop.c

static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
                      Error **errp)
{
    BDRVCloopState *s = bs->opaque;
    uint32_t offsets_size, max_compressed_block_size = 1, i;
    int ret;

    bs->read_only = 1;

    /* read header */
    ret = bdrv_pread(bs->file, 128, &s->block_size, 4);
    if (ret < 0) {
        return ret;
    }
    s->block_size = be32_to_cpu(s->block_size);
    if (s->block_size % 512) {
        error_setg(errp, "block_size %u must be a multiple of 512",
                   s->block_size);
        return -EINVAL;
    }
    if (s->block_size == 0) {
        error_setg(errp, "block_size cannot be zero");
        return -EINVAL;
    }

    /* cloop's create_compressed_fs.c warns about block sizes beyond 256 KB but
     * we can accept more.  Prevent ridiculous values like 4 GB - 1 since we
     * need a buffer this big.
     */
    if (s->block_size > MAX_BLOCK_SIZE) {
        error_setg(errp, "block_size %u must be %u MB or less",
                   s->block_size,
                   MAX_BLOCK_SIZE / (1024 * 1024));
        return -EINVAL;
    }

    ret = bdrv_pread(bs->file, 128 + 4, &s->n_blocks, 4);
    if (ret < 0) {
        return ret;
    }
    s->n_blocks = be32_to_cpu(s->n_blocks);

    /* read offsets */
    offsets_size = s->n_blocks * sizeof(uint64_t);
    s->offsets = g_malloc(offsets_size);

    ret = bdrv_pread(bs->file, 128 + 4 + 4, s->offsets, offsets_size);
    if (ret < 0) {
        goto fail;
    }

    for(i=0;i<s->n_blocks;i++) {
        s->offsets[i] = be64_to_cpu(s->offsets[i]);
        if (i > 0) {
            uint32_t size = s->offsets[i] - s->offsets[i - 1];
            if (size > max_compressed_block_size) {
                max_compressed_block_size = size;
            }
        }
    }

    /* initialize zlib engine */
    s->compressed_block = g_malloc(max_compressed_block_size + 1);
    s->uncompressed_block = g_malloc(s->block_size);
    if (inflateInit(&s->zstream) != Z_OK) {
        ret = -EINVAL;
        goto fail;
    }
    s->current_block = s->n_blocks;

    s->sectors_per_block = s->block_size/512;
    bs->total_sectors = s->n_blocks * s->sectors_per_block;
    qemu_co_mutex_init(&s->lock);
    return 0;

fail:
    g_free(s->offsets);
    g_free(s->compressed_block);
    g_free(s->uncompressed_block);
    return ret;
}