new primitive: vmemdup_user()

similar to memdup_user(), but does *not* guarantee that result will
be physically contiguous; use only in cases where that's not a requirement
and free it with kvfree().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/string.h

@@ -11,6 +11,7 @@
 
 extern char *strndup_user(const char __user *, long);
 extern void *memdup_user(const void __user *, size_t);
+extern void *vmemdup_user(const void __user *, size_t);
 extern void *memdup_user_nul(const void __user *, size_t);
 
 /*

mm/util.c

@@ -150,7 +150,8 @@ EXPORT_SYMBOL(kmemdup_nul);
  * @src: source address in user space
  * @len: number of bytes to copy
  *
- * Returns an ERR_PTR() on failure.
+ * Returns an ERR_PTR() on failure.  Result is physically
+ * contiguous, to be freed by kfree().
  */
 void *memdup_user(const void __user *src, size_t len)
 {
@@ -169,6 +170,32 @@ void *memdup_user(const void __user *src, size_t len)
 }
 EXPORT_SYMBOL(memdup_user);
 
+/**
+ * vmemdup_user - duplicate memory region from user space
+ *
+ * @src: source address in user space
+ * @len: number of bytes to copy
+ *
+ * Returns an ERR_PTR() on failure.  Result may be not
+ * physically contiguous.  Use kvfree() to free.
+ */
+void *vmemdup_user(const void __user *src, size_t len)
+{
+	void *p;
+
+	p = kvmalloc(len, GFP_USER);
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	if (copy_from_user(p, src, len)) {
+		kvfree(p);
+		return ERR_PTR(-EFAULT);
+	}
+
+	return p;
+}
+EXPORT_SYMBOL(vmemdup_user);
+
 /*
  * strndup_user - duplicate an existing string from user space
  * @s: The string to duplicate