The qcow2 header specifies the virtual size of the image in bytes, but BlockDriverState stores it as a number of 512-byte sectors.
If the user tries to create an image with a size that is not a multiple of the sector size then this is fixed on creation by silently rounding the image size up (see commit c2eb918e32). qcow2_co_truncate() is more strict and returns an error instead. However when an image is opened the virtual size is rounded down, which means that trying to access the last few advertised bytes will result in an error. As seen above QEMU cannot create such images and there's no good use case that would require us to try to handle them so let's just treat them as unsupported. Signed-off-by: Alberto Garcia <be...@igalia.com> --- block/qcow2.c | 7 +++++++ docs/interop/qcow2.txt | 3 ++- tests/qemu-iotests/080 | 7 +++++++ tests/qemu-iotests/080.out | 4 ++++ 4 files changed, 20 insertions(+), 1 deletion(-) diff --git a/block/qcow2.c b/block/qcow2.c index 7fbaac8457..92474849db 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -1326,6 +1326,13 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options, goto fail; } + if (header.size % BDRV_SECTOR_SIZE) { + error_setg(errp, "Virtual size is not a multiple of %u", + (unsigned) BDRV_SECTOR_SIZE); + ret = -EINVAL; + goto fail; + } + if (header.header_length > sizeof(header)) { s->unknown_header_fields_size = header.header_length - sizeof(header); s->unknown_header_fields = g_malloc(s->unknown_header_fields_size); diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt index af5711e533..891f5662d8 100644 --- a/docs/interop/qcow2.txt +++ b/docs/interop/qcow2.txt @@ -40,7 +40,8 @@ The first cluster of a qcow2 image contains the file header: with larger cluster sizes. 24 - 31: size - Virtual disk size in bytes. + Virtual disk size in bytes. qemu can only handle + sizes that are a multiple of 512 bytes. Note: qemu has an implementation limit of 32 MB as the maximum L1 table size. With a 2 MB cluster diff --git a/tests/qemu-iotests/080 b/tests/qemu-iotests/080 index 4bcb5021e8..2563b2c052 100755 --- a/tests/qemu-iotests/080 +++ b/tests/qemu-iotests/080 @@ -48,6 +48,7 @@ header_size=104 offset_backing_file_offset=8 offset_backing_file_size=16 +offset_virtual_size=24 offset_l1_size=36 offset_l1_table_offset=40 offset_refcount_table_offset=48 @@ -197,6 +198,12 @@ poke_file "$TEST_IMG" "$offset_snap1_l1_size" "\x10\x00\x00\x00" { $QEMU_IMG snapshot -d test $TEST_IMG; } 2>&1 | _filter_testdir _check_test_img +echo +echo "== Image size not a multiple of the sector size ==" +_make_test_img 64k +poke_file "$TEST_IMG" "$offset_virtual_size" "\x00\x00\x00\x00\x00\x00\xff\xff" +{ $QEMU_IO -c "write 65530 1" $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 45ab01db8e..e1c969e2ba 100644 --- a/tests/qemu-iotests/080.out +++ b/tests/qemu-iotests/080.out @@ -104,4 +104,8 @@ Data may be corrupted, or further writes to the image may corrupt it. 3 leaked clusters were found on the image. This means waste of disk space, but no harm to data. + +== Image size not a multiple of the sector size == +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=65536 +qemu-io: can't open device TEST_DIR/t.qcow2: Virtual size is not a multiple of 512 *** done -- 2.20.1