[PATCH 5.10 185/406] vfio/type1: fix cap_migration information leak

Greg Kroah-Hartman
2023-09-17T19:31:05Z

From: Stefan Hajnoczi <stefanha@redhat.com>

[ Upstream commit cd24e2a60af633f157d7e59c0a6dba64f131c0b1 ]

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>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Fixes: ad721705d09c ("vfio iommu: Add migration capability to report supported features")
Link: https://lore.kernel.org/r/20230801155352.1391945-1-stefanha@redhat.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/vfio/vfio_iommu_type1.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index ec1428dbdf9d9..9b01f88ae4762 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -2659,7 +2659,7 @@ 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 = {};

cap_mig.header.id = VFIO_IOMMU_TYPE1_INFO_CAP_MIGRATION;
cap_mig.header.version = 1;
--
2.40.1