[v4 PATCH 3/3] mm/mempolicy: unify the parameter sanity check for mbind and set_mempolicy

[Feng Tang <feng.tang@xxxxxxxxx>]

Currently the kernel_mbind() and kernel_set_mempolicy() do almost
the same operation for parameter sanity check.

Add a helper function to unify the code to reduce the redundancy,
and make it easier for changing the sanity check code in future.

[thanks to David Rientjes for suggesting using helper function
instead of macro]

Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
---
 mm/mempolicy.c | 48 ++++++++++++++++++++++++++++++------------------
 1 file changed, 30 insertions(+), 18 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 9805291..32ca8fc 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1440,26 +1440,38 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
 	return copy_to_user(mask, nodes_addr(*nodes), copy) ? -EFAULT : 0;
 }
 
+/* Basic parameter sanity check used by both mbind() and set_mempolicy() */
+static inline int sanitize_mpol_flags(int *mode, unsigned short *flags)
+{
+	*flags = *mode & MPOL_MODE_FLAGS;
+	*mode &= ~MPOL_MODE_FLAGS;
+	if ((unsigned int)(*mode) >= MPOL_MAX)
+		return -EINVAL;
+	if ((*flags & MPOL_F_STATIC_NODES) && (*flags & MPOL_F_RELATIVE_NODES))
+		return -EINVAL;
+
+	return 0;
+}
+
 static long kernel_mbind(unsigned long start, unsigned long len,
 			 unsigned long mode, const unsigned long __user *nmask,
 			 unsigned long maxnode, unsigned int flags)
 {
+	unsigned short mode_flags;
 	nodemask_t nodes;
+	int lmode = mode;
 	int err;
-	unsigned short mode_flags;
 
 	start = untagged_addr(start);
-	mode_flags = mode & MPOL_MODE_FLAGS;
-	mode &= ~MPOL_MODE_FLAGS;
-	if (mode >= MPOL_MAX)
-		return -EINVAL;
-	if ((mode_flags & MPOL_F_STATIC_NODES) &&
-	    (mode_flags & MPOL_F_RELATIVE_NODES))
-		return -EINVAL;
+	err = sanitize_mpol_flags(&lmode, &mode_flags);
+	if (err)
+		return err;
+
 	err = get_nodes(&nodes, nmask, maxnode);
 	if (err)
 		return err;
-	return do_mbind(start, len, mode, mode_flags, &nodes, flags);
+
+	return do_mbind(start, len, lmode, mode_flags, &nodes, flags);
 }
 
 SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
@@ -1473,20 +1485,20 @@ SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
 static long kernel_set_mempolicy(int mode, const unsigned long __user *nmask,
 				 unsigned long maxnode)
 {
-	int err;
+	unsigned short mode_flags;
 	nodemask_t nodes;
-	unsigned short flags;
+	int lmode = mode;
+	int err;
+
+	err = sanitize_mpol_flags(&lmode, &mode_flags);
+	if (err)
+		return err;
 
-	flags = mode & MPOL_MODE_FLAGS;
-	mode &= ~MPOL_MODE_FLAGS;
-	if ((unsigned int)mode >= MPOL_MAX)
-		return -EINVAL;
-	if ((flags & MPOL_F_STATIC_NODES) && (flags & MPOL_F_RELATIVE_NODES))
-		return -EINVAL;
 	err = get_nodes(&nodes, nmask, maxnode);
 	if (err)
 		return err;
-	return do_set_mempolicy(mode, flags, &nodes);
+
+	return do_set_mempolicy(lmode, mode_flags, &nodes);
 }
 
 SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long __user *, nmask,
-- 
2.7.4