[Qemu-devel] [PATCH for-2.0 20/47] qcow2: Check backing_file_offset (CVE-2014-0144)

[Stefan Hajnoczi <stefanha@redhat.com>]

From: Kevin Wolf <kwolf@redhat.com>

Header, header extension and the backing file name must all be stored in
the first cluster. Setting the backing file to a much higher value
allowed header extensions to become much bigger than we want them to be
(unbounded allocation).

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2.c              |  6 ++++++
 tests/qemu-iotests/080     | 12 ++++++++++++
 tests/qemu-iotests/080.out |  7 +++++++
 3 files changed, 25 insertions(+)

diff --git a/block/qcow2.c b/block/qcow2.c
index c3c88e9..7571ebf 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -511,6 +511,12 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
         }
     }
 
+    if (header.backing_file_offset > s->cluster_size) {
+        error_setg(errp, "Invalid backing file offset");
+        ret = -EINVAL;
+        goto fail;
+    }
+
     if (header.backing_file_offset) {
         ext_end = header.backing_file_offset;
     } else {
diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080
index 6512701..6d588dd 100755
--- a/tests/qemu-iotests/080
+++ b/tests/qemu-iotests/080
@@ -43,6 +43,8 @@ _supported_proto generic
 _supported_os Linux
 
 header_size=104
+
+offset_backing_file_offset=8
 offset_header_size=100
 offset_ext_magic=$header_size
 offset_ext_size=$((header_size + 4))
@@ -55,6 +57,16 @@ poke_file "$TEST_IMG" "$offset_header_size" "\xff\xff\xff\xff"
 poke_file "$TEST_IMG" "$offset_header_size" "\x7f\xff\xff\xff"
 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
 
+echo
+echo "== Huge unknown header extension =="
+_make_test_img 64M
+poke_file "$TEST_IMG" "$offset_backing_file_offset" "\xff\xff\xff\xff\xff\xff\xff\xff"
+poke_file "$TEST_IMG" "$offset_ext_magic" "\x12\x34\x56\x78"
+poke_file "$TEST_IMG" "$offset_ext_size" "\x7f\xff\xff\xff"
+{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir
+poke_file "$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
+
 # success, all done
 echo "*** done"
 rm -f $seq.full
diff --git a/tests/qemu-iotests/080.out b/tests/qemu-iotests/080.out
index 41a166a..48c40aa 100644
--- a/tests/qemu-iotests/080.out
+++ b/tests/qemu-iotests/080.out
@@ -6,4 +6,11 @@ qemu-io: can't open device TEST_DIR/t.qcow2: qcow2 header exceeds cluster size
 no file open, try 'help open'
 qemu-io: can't open device TEST_DIR/t.qcow2: qcow2 header exceeds cluster size
 no file open, try 'help open'
+
+== Huge unknown header extension ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+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'
 *** done
-- 
1.8.5.3