qcow2: Check refcount table size (CVE-2014-0144)

Limit the in-memory reference count table size to 8 MB, it's enough in
practice. This fixes an unbounded allocation as well as a buffer
overflow in qcow2_refcount_init().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

4 files changed, 29 insertions, 1 deletions

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 4a2df5fb99..e3c7ecdcc9 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -40,8 +40,10 @@ static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
 int qcow2_refcount_init(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
-    int ret, refcount_table_size2, i;
+    unsigned int refcount_table_size2, i;
+    int ret;
 
+    assert(s->refcount_table_size <= INT_MAX / sizeof(uint64_t));
     refcount_table_size2 = s->refcount_table_size * sizeof(uint64_t);
     s->refcount_table = g_malloc(refcount_table_size2);
     if (s->refcount_table_size > 0) {
diff --git a/block/qcow2.c b/block/qcow2.c
index f0411a9217..b9b6e70264 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -577,10 +577,19 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     s->csize_shift = (62 - (s->cluster_bits - 8));
     s->csize_mask = (1 << (s->cluster_bits - 8)) - 1;
     s->cluster_offset_mask = (1LL << s->csize_shift) - 1;
+
     s->refcount_table_offset = header.refcount_table_offset;
     s->refcount_table_size =
         header.refcount_table_clusters << (s->cluster_bits - 3);
 
+    if (header.refcount_table_clusters > (0x800000 >> s->cluster_bits)) {
+        /* 8 MB refcount table is enough for 2 PB images at 64k cluster size
+         * (128 GB for 512 byte clusters, 2 EB for 2 MB clusters) */
+        error_setg(errp, "Reference count table too large");
+        ret = -EINVAL;
+        goto fail;
+    }
+
     s->snapshots_offset = header.snapshots_offset;
     s->nb_snapshots = header.nb_snapshots;
 
diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080
index 6d588ddd12..6179e0519f 100755
--- a/tests/qemu-iotests/080
+++ b/tests/qemu-iotests/080
@@ -45,6 +45,7 @@ _supported_os Linux
 header_size=104
 
 offset_backing_file_offset=8
+offset_refcount_table_clusters=56
 offset_header_size=100
 offset_ext_magic=$header_size
 offset_ext_size=$((header_size + 4))
@@ -67,6 +68,15 @@ poke_file "$TEST_IMG" "$offset_ext_size" "\x7f\xff\xff\xff"
 poke_file "$TEST_IMG" "$offset_backing_file_offset" "\x00\x00\x00\x00\x00\x00\x00\x00"
 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== Huge refcount table size =="
+_make_test_img 64M
+poke_file "$TEST_IMG" "$offset_refcount_table_clusters" "\xff\xff\xff\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+poke_file "$TEST_IMG" "$offset_refcount_table_clusters" "\x00\x02\x00\x01"
+{ $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/080.out b/tests/qemu-iotests/080.out
index 48c40aa3e2..6fef6d9892 100644
--- a/tests/qemu-iotests/080.out
+++ b/tests/qemu-iotests/080.out
@@ -13,4 +13,11 @@ qemu-io: can't open device TEST_DIR/t.qcow2: Invalid backing file offset
 no file open, try 'help open'
 qemu-io: can't open device TEST_DIR/t.qcow2: Header extension too large
 no file open, try 'help open'
+
+== Huge refcount table size ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+qemu-io: can't open device TEST_DIR/t.qcow2: Reference count table too large
+no file open, try 'help open'
+qemu-io: can't open device TEST_DIR/t.qcow2: Reference count table too large
+no file open, try 'help open'
 *** done