NFS: Clean up nfs_permission().

 Fix a bug whereby we are failing to test for permissions on opendir().
 Optimize away permissions checks that request MAY_WRITE on directories.
 Ensure that VFS sets LOOKUP_CONTINUE before calling permission().
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/dir.c

@@ -1498,21 +1498,34 @@ static int nfs_do_access(struct inode *inode, struct rpc_cred *cred, int mask)
 int nfs_permission(struct inode *inode, int mask, struct nameidata *nd)
 {
 	struct rpc_cred *cred;
-	int res;
+	int res = 0;
 
 	if (mask == 0)
-		return 0;
+		goto out;
+	/* Is this sys_access() ? */
+	if (nd != NULL && (nd->flags & LOOKUP_ACCESS))
+		goto force_lookup;
 
-	/* Are we checking permissions on anything other than lookup/execute? */
-	if ((mask & MAY_EXEC) == 0) {
-		/* We only need to check permissions on file open() and access() */
-		if (!nd || !(nd->flags & (LOOKUP_OPEN|LOOKUP_ACCESS)))
-			return 0;
+	switch (inode->i_mode & S_IFMT) {
+		case S_IFLNK:
+			goto out;
+		case S_IFREG:
 			/* NFSv4 has atomic_open... */
-		if (NFS_PROTO(inode)->version > 3 && (nd->flags & LOOKUP_OPEN))
-			return 0;
+			if (nfs_server_capable(inode, NFS_CAP_ATOMIC_OPEN)
+					&& nd != NULL
+					&& (nd->flags & LOOKUP_OPEN))
+				goto out;
+			break;
+		case S_IFDIR:
+			/*
+			 * Optimize away all write operations, since the server
+			 * will check permissions when we perform the op.
+			 */
+			if ((mask & MAY_WRITE) && !(mask & MAY_READ))
+				goto out;
 	}
 
+force_lookup:
 	lock_kernel();
 
 	if (!NFS_PROTO(inode)->access)
@@ -1522,6 +1535,7 @@ int nfs_permission(struct inode *inode, int mask, struct nameidata *nd)
 	res = nfs_do_access(inode, cred, mask);
 	put_rpccred(cred);
 	unlock_kernel();
+out:
 	return res;
 out_notsup:
 	nfs_revalidate_inode(NFS_SERVER(inode), inode);

fs/nfs/inode.c

@@ -1542,6 +1542,7 @@ static int nfs4_fill_super(struct super_block *sb, struct nfs4_mount_data *data,
 	if (data->wsize != 0)
 		server->wsize = nfs_block_size(data->wsize, NULL);
 	server->flags = data->flags & NFS_MOUNT_FLAGMASK;
+	server->caps = NFS_CAP_ATOMIC_OPEN;
 
 	server->acregmin = data->acregmin*HZ;
 	server->acregmax = data->acregmax*HZ;

include/linux/nfs_fs_sb.h

@@ -53,5 +53,6 @@ struct nfs_server {
 #define NFS_CAP_HARDLINKS	(1U << 1)
 #define NFS_CAP_SYMLINKS	(1U << 2)
 #define NFS_CAP_ACLS		(1U << 3)
+#define NFS_CAP_ATOMIC_OPEN	(1U << 4)
 
 #endif