Re: [PATCH] vfio/type1: fix cap_migration information leak

Alex Williamson
2023-08-17T17:57:11Z

On Tue, 1 Aug 2023 11:53:52 -0400
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> Fix an information leak where an uninitialized hole in struct
> vfio_iommu_type1_info_cap_migration on the stack is exposed to userspace.
>
> The definition of struct vfio_iommu_type1_info_cap_migration contains a hole as
> shown in this pahole(1) output:
>
> struct vfio_iommu_type1_info_cap_migration {
> struct vfio_info_cap_header header; /* 0 8 */
> __u32 flags; /* 8 4 */
>
> /* XXX 4 bytes hole, try to pack */
>
> __u64 pgsize_bitmap; /* 16 8 */
> __u64 max_dirty_bitmap_size; /* 24 8 */
>
> /* size: 32, cachelines: 1, members: 4 */
> /* sum members: 28, holes: 1, sum holes: 4 */
> /* last cacheline: 32 bytes */
> };
>
> The cap_mig variable is filled in without initializing the hole:
>
> static int vfio_iommu_migration_build_caps(struct vfio_iommu *iommu,
> struct vfio_info_cap *caps)
> {
> struct vfio_iommu_type1_info_cap_migration cap_mig;
>
> cap_mig.header.id = VFIO_IOMMU_TYPE1_INFO_CAP_MIGRATION;
> cap_mig.header.version = 1;
>
> cap_mig.flags = 0;
> /* support minimum pgsize */
> cap_mig.pgsize_bitmap = (size_t)1 << __ffs(iommu->pgsize_bitmap);
> cap_mig.max_dirty_bitmap_size = DIRTY_BITMAP_SIZE_MAX;
>
> return vfio_info_add_capability(caps, &cap_mig.header, sizeof(cap_mig));
> }
>
> The structure is then copied to a temporary location on the heap. At this point
> it's already too late and ioctl(VFIO_IOMMU_GET_INFO) copies it to userspace
> later:
>
> int vfio_info_add_capability(struct vfio_info_cap *caps,
> struct vfio_info_cap_header *cap, size_t size)
> {
> struct vfio_info_cap_header *header;
>
> header = vfio_info_cap_add(caps, size, cap->id, cap->version);
> if (IS_ERR(header))
> return PTR_ERR(header);
>
> memcpy(header + 1, cap + 1, size - sizeof(*header));
>
> return 0;
> }
>
> This issue was found by code inspection.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Applied to vfio next branch for v6.6. I'll give Jason a little more
time to ack "[PATCH v3] vfio: align capability structures". Thanks!

Alex

>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index ebe0ad31d0b0..d662aa9d1b4b 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -2732,7 +2732,7 @@ static int vfio_iommu_iova_build_caps(struct vfio_iommu *iommu,
> static int vfio_iommu_migration_build_caps(struct vfio_iommu *iommu,
> struct vfio_info_cap *caps)
> {
> - struct vfio_iommu_type1_info_cap_migration cap_mig;
> + struct vfio_iommu_type1_info_cap_migration cap_mig = {};