block/cloop: prevent offsets_size integer overflow (CVE-2014-0143)

The following integer overflow in offsets_size can lead to out-of-bounds
memory stores when n_blocks has a huge value:

    uint32_t n_blocks, offsets_size;
    [...]
    ret = bdrv_pread(bs->file, 128 + 4, &s->n_blocks, 4);
    [...]
    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);

    [...]

    for(i=0;i<s->n_blocks;i++) {
        s->offsets[i] = be64_to_cpu(s->offsets[i]);

offsets_size can be smaller than n_blocks due to integer overflow.
Therefore s->offsets[] is too small when the for loop byteswaps offsets.

This patch refuses to open files if offsets_size would overflow.

Note that changing the type of offsets_size is not a fix since 32-bit
hosts still only have 32-bit size_t.

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>

1 files changed, 7 insertions, 0 deletions

diff --git a/tests/qemu-iotests/075 b/tests/qemu-iotests/075
index 8f54a99b14..9ce6b1fb8c 100755
--- a/tests/qemu-iotests/075
+++ b/tests/qemu-iotests/075
@@ -43,6 +43,7 @@ _supported_proto generic
 _supported_os Linux
 
 block_size_offset=128
+n_blocks_offset=132
 
 echo
 echo "== check that the first sector can be read =="
@@ -67,6 +68,12 @@ _use_sample_img simple-pattern.cloop.bz2
 poke_file "$TEST_IMG" "$block_size_offset" "\xff\xff\xfe\x00"
 $QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== offsets_size overflow ==="
+_use_sample_img simple-pattern.cloop.bz2
+poke_file "$TEST_IMG" "$n_blocks_offset" "\xff\xff\xff\xff"
+$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
+
 # success, all done
 echo "*** done"
 rm -f $seq.full