From 6906046169ffa9d829beeeaafe1fadeba51669fb Mon Sep 17 00:00:00 2001 From: Jeff Cody Date: Tue, 13 May 2014 10:00:52 -0400 Subject: block: vhdx - account for identical header sections MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The VHDX spec v1.00 declares that "a header is current if it is the only valid header or if it is valid and its SequenceNumber field is greater than the other header’s SequenceNumber field. The parser must only use data from the current header. If there is no current header, then the VHDX file is corrupt." However, the Disk2VHD tool from Microsoft creates a VHDX image file that has 2 identical headers, including matching checksums and matching sequence numbers. Likely, as a shortcut the tool is just writing the header twice, for the active and inactive headers, during the image creation. Technically, this should be considered a corrupt VHDX file (at least per the 1.00 spec, and that is how we currently treat it). But in order to accomodate images created with Disk2VHD, we can safely create an exception for this case. If we find identical sequence numbers, then we check the VHDXHeader-sized chunks of each 64KB header sections (we won't rely just on the crc32c to indicate the headers are the same). If they are identical, then we go ahead and use the first one. Reported-by: Nerijus Baliūnas Signed-off-by: Jeff Cody Signed-off-by: Kevin Wolf --- block/vhdx.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'block/vhdx.c') diff --git a/block/vhdx.c b/block/vhdx.c index 509baaf484..353c74d35f 100644 --- a/block/vhdx.c +++ b/block/vhdx.c @@ -473,7 +473,14 @@ static void vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s, } else if (h2_seq > h1_seq) { s->curr_header = 1; } else { - goto fail; + /* The Microsoft Disk2VHD tool will create 2 identical + * headers, with identical sequence numbers. If the headers are + * identical, don't consider the file corrupt */ + if (!memcmp(header1, header2, sizeof(VHDXHeader))) { + s->curr_header = 0; + } else { + goto fail; + } } } -- cgit v1.2.3