NFS: Fix the ftruncate() credential problem

ftruncate() access checking is supposed to be performed at open() time,
just like reads and writes.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 596c5d8..2e4ab4a 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -347,7 +347,7 @@
 	goto out;
 }
 
-#define NFS_VALID_ATTRS (ATTR_MODE|ATTR_UID|ATTR_GID|ATTR_SIZE|ATTR_ATIME|ATTR_ATIME_SET|ATTR_MTIME|ATTR_MTIME_SET)
+#define NFS_VALID_ATTRS (ATTR_MODE|ATTR_UID|ATTR_GID|ATTR_SIZE|ATTR_ATIME|ATTR_ATIME_SET|ATTR_MTIME|ATTR_MTIME_SET|ATTR_FILE)
 
 int
 nfs_setattr(struct dentry *dentry, struct iattr *attr)
@@ -369,7 +369,7 @@
 
 	/* Optimization: if the end result is no change, don't RPC */
 	attr->ia_valid &= NFS_VALID_ATTRS;
-	if (attr->ia_valid == 0)
+	if ((attr->ia_valid & ~ATTR_FILE) == 0)
 		return 0;
 
 	lock_kernel();