fs: rework getname_kernel to handle up to PATH_MAX sized filenames

In preparation for expanded use in the kernel, make getname_kernel()
more useful by allowing it to handle any legal filename length.

Thanks to Guenter Roeck for his suggestion to substitute memcpy() for
strlcpy().

CC: linux@roeck-us.net
CC: viro@zeniv.linux.org.uk
CC: linux-fsdevel@vger.kernel.org
Signed-off-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -212,32 +212,38 @@ getname(const char __user * filename)
 	return getname_flags(filename, 0, NULL);
 }
 
-/*
- * The "getname_kernel()" interface doesn't do pathnames longer
- * than EMBEDDED_NAME_MAX. Deal with it - you're a kernel user.
- */
 struct filename *
 getname_kernel(const char * filename)
 {
 	struct filename *result;
-	char *kname;
-	int len;
-
-	len = strlen(filename);
-	if (len >= EMBEDDED_NAME_MAX)
-		return ERR_PTR(-ENAMETOOLONG);
+	int len = strlen(filename) + 1;
 
 	result = __getname();
 	if (unlikely(!result))
 		return ERR_PTR(-ENOMEM);
 
-	kname = (char *)result + sizeof(*result);
-	result->name = kname;
+	if (len <= EMBEDDED_NAME_MAX) {
+		result->name = (char *)(result) + sizeof(*result);
+		result->separate = false;
+	} else if (len <= PATH_MAX) {
+		struct filename *tmp;
+
+		tmp = kmalloc(sizeof(*tmp), GFP_KERNEL);
+		if (unlikely(!tmp)) {
+			__putname(result);
+			return ERR_PTR(-ENOMEM);
+		}
+		tmp->name = (char *)result;
+		tmp->separate = true;
+		result = tmp;
+	} else {
+		__putname(result);
+		return ERR_PTR(-ENAMETOOLONG);
+	}
+	memcpy((char *)result->name, filename, len);
 	result->uptr = NULL;
 	result->aname = NULL;
-	result->separate = false;
 
-	strlcpy(kname, filename, EMBEDDED_NAME_MAX);
 	return result;
 }