[PATCH] NFS: fix bogus setattr calls

From: Trond Myklebust <trond.myklebust@fys.uio.no>

If users set the execute bit on a file, and then write to it,
remove_suid() causes a flood of SETATTR calls (one per write() syscall)
with no arguments to be sent down the wire.

The server will in any case clear the suid bit itself without any
prompting from us, so the following patch simply filters away all
SETATTR requests with empty or unsupported ia_valid fields.

fs/nfs/inode.c

@@ -791,6 +791,8 @@ nfs_fhget(struct super_block *sb, struct nfs_fh *fh, struct nfs_fattr *fattr)
 	goto out;
 }
 
+#define NFS_VALID_ATTRS (ATTR_MODE|ATTR_UID|ATTR_GID|ATTR_SIZE|ATTR_ATIME|ATTR_ATIME_SET|ATTR_MTIME|ATTR_MTIME_SET)
+
 int
 nfs_setattr(struct dentry *dentry, struct iattr *attr)
 {
@@ -798,6 +800,11 @@ nfs_setattr(struct dentry *dentry, struct iattr *attr)
 	struct nfs_fattr fattr;
 	int error;
 
+	/* Optimization: if the end result is no change, don't RPC */
+	attr->ia_valid &= NFS_VALID_ATTRS;
+	if (attr->ia_valid == 0)
+		return 0;
+
 	lock_kernel();
 
 	/*
@@ -813,6 +820,8 @@ printk("nfs_setattr: revalidate failed, error=%d\n", error);
 
 	if (!S_ISREG(inode->i_mode)) {
 		attr->ia_valid &= ~ATTR_SIZE;
+		if (attr->ia_valid == 0)
+			goto out;
 	} else {
 		filemap_fdatawrite(inode->i_mapping);
 		error = nfs_wb_all(inode);