[Qemu-devel] [PATCH 3/5] qcow1: Validate L2 table size (CVE-2014-0222)

[Kevin Wolf <kwolf@redhat.com>]

Too large L2 table sizes cause unbounded allocations. Images actually
created by qemu-img only have 512 byte or 4k L2 tables.

To keep things consistent with cluster sizes, allow ranges between 512
bytes and 64k (in fact, down to 1 entry = 8 bytes is technically
working, but L2 table sizes smaller than a cluster don't make a lot of
sense).

This also means that the number of bytes on the virtual disk that are
described by the same L2 table is limited to at most 8k * 64k or 2^29,
preventively avoiding any integer overflows.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow.c               |  8 ++++++++
 tests/qemu-iotests/092     | 10 ++++++++++
 tests/qemu-iotests/092.out |  7 +++++++
 3 files changed, 25 insertions(+)

diff --git a/block/qcow.c b/block/qcow.c
index e60df23..e8038e5 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -139,6 +139,14 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    /* l2_bits specifies number of entries; storing a uint64_t in each entry,
+     * so bytes = num_entries << 3. */
+    if (header.l2_bits < 9 - 3 || header.l2_bits > 16 - 3) {
+        error_setg(errp, "L2 table size must be between 512 and 64k");
+        ret = -EINVAL;
+        goto fail;
+    }
+
     if (header.crypt_method > QCOW_CRYPT_AES) {
         error_setg(errp, "invalid encryption method in qcow header");
         ret = -EINVAL;
diff --git a/tests/qemu-iotests/092 b/tests/qemu-iotests/092
index b0f04e3..2196cce 100755
--- a/tests/qemu-iotests/092
+++ b/tests/qemu-iotests/092
@@ -54,6 +54,16 @@ poke_file "$TEST_IMG" "$offset_cluster_bits" "\xff"
 poke_file "$TEST_IMG" "$offset_cluster_bits" "\x1f"
 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== Invalid L2 table size =="
+_make_test_img 64M
+poke_file "$TEST_IMG" "$offset_l2_bits" "\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+
+# 1 << 0x1b = 2^31 / L2_CACHE_SIZE
+poke_file "$TEST_IMG" "$offset_l2_bits" "\x1b"
+{ $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/092.out b/tests/qemu-iotests/092.out
index 9e7367a..45a7ac8 100644
--- a/tests/qemu-iotests/092.out
+++ b/tests/qemu-iotests/092.out
@@ -6,4 +6,11 @@ qemu-io: can't open device TEST_DIR/t.qcow: Cluster size must be between 512 and
 no file open, try 'help open'
 qemu-io: can't open device TEST_DIR/t.qcow: Cluster size must be between 512 and 64k
 no file open, try 'help open'
+
+== Invalid L2 table size ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+qemu-io: can't open device TEST_DIR/t.qcow: L2 table size must be between 512 and 64k
+no file open, try 'help open'
+qemu-io: can't open device TEST_DIR/t.qcow: L2 table size must be between 512 and 64k
+no file open, try 'help open'
 *** done
-- 
1.8.3.1