[Xen-devel] [PATCH] xen/privcmd: fix static checker warning

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

Commit 3ad0876554ca ("xen/privcmd: add IOCTL_PRIVCMD_MMAP_RESOURCE")
introduced a static checker warning:

  drivers/xen/privcmd.c:827 privcmd_ioctl_mmap_resource()
  warn: passing casted pointer 'pfns' to 'xen_remap_domain_mfn_array()'
        64 vs 32.

caused by this cast:

   827  num = xen_remap_domain_mfn_array(vma,
   828                                   kdata.addr & PAGE_MASK,
   829                                   pfns, kdata.num, (int *)pfns,
                                                          ^^^^^^^^^^^

The reason for the cast is that xen_remap_domain_mfn_array() requires an
array of ints to store error codes. It is actually safe to re-use the
pfns array for this purpose but it does look odd (as well as leading to
the warning). It would also be easy for a future implementation change
to make this re-use unsafe so this patch modifies privcmd to use a
separately allocated array for error codes.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
---
 drivers/xen/privcmd.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 8ae0349..8507c13 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -822,11 +822,18 @@ static long privcmd_ioctl_mmap_resource(struct file 
*file, void __user *udata)
                unsigned int domid =
                        (xdata.flags & XENMEM_rsrc_acq_caller_owned) ?
                        DOMID_SELF : kdata.dom;
+               int *errs;
                int num;
 
+               errs = kcalloc(kdata.num, sizeof(*errs), GFP_KERNEL);
+               if (!errs) {
+                       rc = -ENOMEM;
+                       goto out;
+               }
+
                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);
@@ -836,12 +843,14 @@ static long privcmd_ioctl_mmap_resource(struct file 
*file, void __user *udata)
                        unsigned int i;
 
                        for (i = 0; i < num; i++) {
-                               rc = pfns[i];
+                               rc = errs[i];
                                if (rc < 0)
                                        break;
                        }
                } else
                        rc = 0;
+
+               kfree(errs);
        }
 
 out:
-- 
2.1.4


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