[Qemu-devel] [PATCH v2 1/3] qcow2: Fix header extension size check

[Kevin Wolf <kwolf@redhat.com>]

After reading the extension header, offset is incremented, but not
checked against end_offset any more. This way an integer overflow could
happen when checking whether the extension end is within the allowed
range, effectively disabling the check.

This patch adds the missing check and a test case for it.

Cc: qemu-stable@nongnu.org
Reported-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2.c              | 2 +-
 tests/qemu-iotests/080     | 2 ++
 tests/qemu-iotests/080.out | 2 ++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index d120494..8b9ffc4 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -117,7 +117,7 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
 #ifdef DEBUG_EXT
         printf("ext.magic = 0x%x\n", ext.magic);
 #endif
-        if (ext.len > end_offset - offset) {
+        if (offset > end_offset || ext.len > end_offset - offset) {
             error_setg(errp, "Header extension too large");
             return -EINVAL;
         }
diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080
index 9de337c..73795f1 100755
--- a/tests/qemu-iotests/080
+++ b/tests/qemu-iotests/080
@@ -78,6 +78,8 @@ poke_file "$TEST_IMG" "$offset_backing_file_offset" "\xff\xff\xff\xff\xff\xff\xf
 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" "$offset_backing_file_offset" "\x00\x00\x00\x00\x00\x00\x00\x$(printf %x $offset_ext_size)"
+{ $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
 
diff --git a/tests/qemu-iotests/080.out b/tests/qemu-iotests/080.out
index f7a943c..33d1f71 100644
--- a/tests/qemu-iotests/080.out
+++ b/tests/qemu-iotests/080.out
@@ -13,6 +13,8 @@ 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'
+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 
-- 
1.8.3.1