linux-kernel - [PATCH] xen/privcmd: fix static checker warning

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Date:   Thu, 7 Jun 2018 11:21:13 +0100
From:   Paul Durrant <paul.durrant@...rix.com>
To:     <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
CC:     Paul Durrant <paul.durrant@...rix.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: [PATCH] xen/privcmd: fix static checker warning

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@...cle.com>
Signed-off-by: Paul Durrant <paul.durrant@...rix.com>
---
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Dan Carpenter <dan.carpenter@...cle.com>
---
 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