[PATCH 2/3] xen/privcmd: fix error handling in mmap-resource processing

[Jan Beulich <jbeulich@xxxxxxxx>]

xen_pfn_t is the same size as int only on 32-bit builds (and not even
on Arm32). Hence pfns[] can't be used directly to read individual error
values returned from xen_remap_domain_mfn_array(); every other error
indicator would be skipped/ignored on 64-bit.

Fixes: 3ad0876554ca ("xen/privcmd: add IOCTL_PRIVCMD_MMAP_RESOURCE")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -803,11 +803,12 @@ static long privcmd_ioctl_mmap_resource(
                unsigned int domid =
                        (xdata.flags & XENMEM_rsrc_acq_caller_owned) ?
                        DOMID_SELF : kdata.dom;
-               int num;
+               int num, *errs = (int *)pfns;
 
+               BUILD_BUG_ON(sizeof(*errs) > sizeof(*pfns));
                num = xen_remap_domain_mfn_array(vma,
                                                 kdata.addr & PAGE_MASK,
-                                                pfns, kdata.num, (int *)pfns,
+                                                pfns, kdata.num, errs,
                                                 vma->vm_page_prot,
                                                 domid,
                                                 vma->vm_private_data);
@@ -817,7 +818,7 @@ static long privcmd_ioctl_mmap_resource(
                        unsigned int i;
 
                        for (i = 0; i < num; i++) {
-                               rc = pfns[i];
+                               rc = errs[i];
                                if (rc < 0)
                                        break;
                        }