[Qemu-devel] [PATCH for-2.0 04/47] block/cloop: prevent offsets_size integer overflow (CVE-2014-0143)

[Stefan Hajnoczi <stefanha@redhat.com>]

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>
---
 block/cloop.c              | 7 +++++++
 tests/qemu-iotests/075     | 7 +++++++
 tests/qemu-iotests/075.out | 4 ++++
 3 files changed, 18 insertions(+)

diff --git a/block/cloop.c b/block/cloop.c
index f021663..563e916 100644
--- a/block/cloop.c
+++ b/block/cloop.c
@@ -99,6 +99,13 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
     s->n_blocks = be32_to_cpu(s->n_blocks);
 
     /* read offsets */
+    if (s->n_blocks > UINT32_MAX / sizeof(uint64_t)) {
+        /* Prevent integer overflow */
+        error_setg(errp, "n_blocks %u must be %zu or less",
+                   s->n_blocks,
+                   UINT32_MAX / sizeof(uint64_t));
+        return -EINVAL;
+    }
     offsets_size = s->n_blocks * sizeof(uint64_t);
     s->offsets = g_malloc(offsets_size);
 
diff --git a/tests/qemu-iotests/075 b/tests/qemu-iotests/075
index 8f54a99..9ce6b1f 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
diff --git a/tests/qemu-iotests/075.out b/tests/qemu-iotests/075.out
index d362c95..a771789 100644
--- a/tests/qemu-iotests/075.out
+++ b/tests/qemu-iotests/075.out
@@ -15,4 +15,8 @@ no file open, try 'help open'
 == huge block_size ===
 qemu-io: can't open device TEST_DIR/simple-pattern.cloop: block_size 4294966784 must be 64 MB or less
 no file open, try 'help open'
+
+== offsets_size overflow ===
+qemu-io: can't open device TEST_DIR/simple-pattern.cloop: n_blocks 4294967295 must be 536870911 or less
+no file open, try 'help open'
 *** done
-- 
1.8.5.3