Re: [PATCH] block/vhdx: Add alignment checks for region tables

[Eric Blake <eblake@redhat.com>]

On Wed, Nov 11, 2026 at 05:14:42PM +0100, Thomas Huth wrote:
> According to the VHDX specification:
> 
>  "The FileOffset and Length fields specify the 64-bit byte offset and 32-bit
>   byte length of the object within the file. The values must be a multiple of
>   1 MB, and FileOffset must be at least 1 MB."
> 
> Thus let's add a sanity check to avoid that bad things could happen later.
> 
> Buglink: https://gitlab.com/qemu-project/qemu/-/work_items/3762
> Reported-by: Daniel Wade <danjwade95@gmail.com>
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  block/vhdx.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/block/vhdx.c b/block/vhdx.c
> index 8013a90a1a4..f5beace56f5 100644
> --- a/block/vhdx.c
> +++ b/block/vhdx.c
> @@ -566,6 +566,16 @@ vhdx_open_region_tables(BlockDriverState *bs, BDRVVHDXState *s)
>  
>          vhdx_region_entry_le_import(&rt_entry);
>  
> +        /*
> +         * According to the VHDX spec, offset and length must be multiple
> +         * of 1 MiB and length must be at least 1 MiB.
> +         */
> +        if ((rt_entry.file_offset & (MiB - 1)) ||
> +            (rt_entry.length & (MiB - 1)) || rt_entry.length < MiB) {

Would QEMU_IS_ALIGNED() be better than open-coding the math here?
Also, the 'rt_entry.length < MiB' clause could be simplified to
'rt_entry.length == 0', since all other values less than MiB fail the
earlier alignment clause.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org