qcow2: Check maximum L1 size in qcow2_snapshot_load_tmp() (CVE-2014-0143)

This avoids an unbounded allocation.

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

block/qcow2-snapshot.c

@@ -680,6 +680,10 @@ int qcow2_snapshot_load_tmp(BlockDriverState *bs,
     sn = &s->snapshots[snapshot_index];
 
     /* Allocate and read in the snapshot's L1 table */
+    if (sn->l1_size > QCOW_MAX_L1_SIZE) {
+        error_setg(errp, "Snapshot L1 table too large");
+        return -EFBIG;
+    }
     new_l1_bytes = sn->l1_size * sizeof(uint64_t);
     new_l1_table = g_malloc0(align_offset(new_l1_bytes, 512));
 

block/qcow2.c

@@ -638,9 +638,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     /* read the level 1 table */
-    if (header.l1_size > 0x2000000) {
+    if (header.l1_size > QCOW_MAX_L1_SIZE) {
-        /* 32 MB L1 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, "Active L1 table too large");
         ret = -EFBIG;
         goto fail;

block/qcow2.h

@@ -44,6 +44,10 @@
  * (128 GB for 512 byte clusters, 2 EB for 2 MB clusters) */
 #define QCOW_MAX_REFTABLE_SIZE 0x800000
 
+/* 32 MB L1 table is enough for 2 PB images at 64k cluster size
+ * (128 GB for 512 byte clusters, 2 EB for 2 MB clusters) */
+#define QCOW_MAX_L1_SIZE 0x2000000
+
 /* indicate that the refcount of the referenced cluster is exactly one. */
 #define QCOW_OFLAG_COPIED     (1ULL << 63)
 /* indicate that the cluster is compressed (they never have the copied flag) */

tests/qemu-iotests/080

@@ -30,7 +30,8 @@ status=1	# failure is the default!
 
 _cleanup()
 {
-	_cleanup_test_img
+    rm -f $TEST_IMG.snap
+    _cleanup_test_img
 }
 trap "_cleanup; exit \$status" 0 1 2 3 15
 
@@ -58,6 +59,10 @@ offset_ext_size=$((header_size + 4))
 
 offset_l2_table_0=$((0x40000))
 
+offset_snap1=$((0x70000))
+offset_snap1_l1_offset=$((offset_snap1 + 0))
+offset_snap1_l1_size=$((offset_snap1 + 8))
+
 echo
 echo "== Huge header size =="
 _make_test_img 64M
@@ -161,6 +166,14 @@ poke_file "$TEST_IMG" "$offset_l2_table_0" "\xbf\xff\xff\xff\xff\xff\x00\x00"
 poke_file "$TEST_IMG" "$offset_l2_table_0" "\x80\x00\x00\xff\xff\xff\x00\x00"
 { $QEMU_IMG snapshot -c test $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== Invalid snapshot L1 table =="
+_make_test_img 64M
+{ $QEMU_IO -c "write 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+{ $QEMU_IMG snapshot -c test $TEST_IMG; } 2>&1 | _filter_testdir
+poke_file "$TEST_IMG" "$offset_snap1_l1_size" "\x10\x00\x00\x00"
+{ $QEMU_IMG convert -s test $TEST_IMG $TEST_IMG.snap; } 2>&1 | _filter_testdir
+
 # success, all done
 echo "*** done"
 rm -f $seq.full

tests/qemu-iotests/080.out

@@ -74,4 +74,10 @@ wrote 512/512 bytes at offset 0
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 qemu-img: Could not create snapshot 'test': -27 (File too large)
 qemu-img: Could not create snapshot 'test': -11 (Resource temporarily unavailable)
+
+== Invalid snapshot L1 table ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+wrote 512/512 bytes at offset 0
+512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+qemu-img: Failed to load snapshot: Snapshot L1 table too large
 *** done