[Qemu-devel] [PATCH for-2.0 42/47] qcow2: Fix NULL dereference in qcow2_open() error path (CVE-2014-0146)

[Stefan Hajnoczi]

From: Kevin Wolf <address@hidden>

The qcow2 code assumes that s->snapshots is non-NULL if s->nb_snapshots
!= 0. By having the initialisation of both fields separated in
qcow2_open(), any error occuring in between would cause the error path
to dereference NULL in qcow2_free_snapshots() if the image had any
snapshots.

Signed-off-by: Kevin Wolf <address@hidden>
---
 block/qcow2.c              | 7 ++++---
 tests/qemu-iotests/080     | 7 +++++++
 tests/qemu-iotests/080.out | 4 ++++
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 6c54e2b..7a75398 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -636,9 +636,6 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, 
int flags,
         goto fail;
     }
 
-    s->snapshots_offset = header.snapshots_offset;
-    s->nb_snapshots = header.nb_snapshots;
-
     /* read the level 1 table */
     if (header.l1_size > 0x2000000) {
         /* 32 MB L1 table is enough for 2 PB images at 64k cluster size
@@ -733,6 +730,10 @@ static int qcow2_open(BlockDriverState *bs, QDict 
*options, int flags,
         bs->backing_file[len] = '\0';
     }
 
+    /* Internal snapshots */
+    s->snapshots_offset = header.snapshots_offset;
+    s->nb_snapshots = header.nb_snapshots;
+
     ret = qcow2_read_snapshots(bs);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not read snapshots");
diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080
index 56f8903..59e7a44 100755
--- a/tests/qemu-iotests/080
+++ b/tests/qemu-iotests/080
@@ -139,6 +139,13 @@ poke_file "$TEST_IMG" "$offset_l1_size" "\x00\x00\x00\x01"
 { $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | 
_filter_testdir
 
 echo
+echo "== Invalid L1 table (with internal snapshot in the image) =="
+_make_test_img 64M
+{ $QEMU_IMG snapshot -c foo $TEST_IMG; } 2>&1 | _filter_qemu_io | 
_filter_testdir
+poke_file "$TEST_IMG" "$offset_l1_size" "\x00\x00\x00\x00"
+_img_info
+
+echo
 echo "== Invalid backing file size =="
 _make_test_img 64M
 poke_file "$TEST_IMG" "$offset_backing_file_offset" 
"\x00\x00\x00\x00\x00\x00\x10\x00"
diff --git a/tests/qemu-iotests/080.out b/tests/qemu-iotests/080.out
index 303d6c3..4d84fbf 100644
--- a/tests/qemu-iotests/080.out
+++ b/tests/qemu-iotests/080.out
@@ -59,6 +59,10 @@ no file open, try 'help open'
 qemu-io: can't open device TEST_DIR/t.qcow2: Invalid L1 table offset
 no file open, try 'help open'
 
+== Invalid L1 table (with internal snapshot in the image) ==
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
+qemu-img: Could not open 'TEST_DIR/t.IMGFMT': L1 table is too small
+
 == Invalid backing file size ==
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
 qemu-io: can't open device TEST_DIR/t.qcow2: Backing file name too long
-- 
1.8.5.3