nfsd: check d_can_lookup in fh_verify of directories

Create and other nfsd ops generally assume we can call lookup_one_len on
inodes with S_IFDIR set.  Al says that this assumption isn't true in
general, though it should be for the filesystem objects nfsd sees.

Add a check just to make sure our assumption isn't violated.

Remove a couple checks for i_op->lookup in create code.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfsfh.c

@@ -59,14 +59,20 @@ static int nfsd_acceptable(void *expv, struct dentry *dentry)
  * the write call).
  */
 static inline __be32
-nfsd_mode_check(struct svc_rqst *rqstp, umode_t mode, umode_t requested)
+nfsd_mode_check(struct svc_rqst *rqstp, struct dentry *dentry,
+		umode_t requested)
 {
-	mode &= S_IFMT;
+	umode_t mode = d_inode(dentry)->i_mode & S_IFMT;
 
 	if (requested == 0) /* the caller doesn't care */
 		return nfs_ok;
-	if (mode == requested)
+	if (mode == requested) {
+		if (mode == S_IFDIR && !d_can_lookup(dentry)) {
+			WARN_ON_ONCE(1);
+			return nfserr_notdir;
+		}
 		return nfs_ok;
+	}
 	/*
 	 * v4 has an error more specific than err_notdir which we should
 	 * return in preference to err_notdir:
@@ -340,7 +346,7 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type, int access)
 	if (error)
 		goto out;
 
-	error = nfsd_mode_check(rqstp, d_inode(dentry)->i_mode, type);
+	error = nfsd_mode_check(rqstp, dentry, type);
 	if (error)
 		goto out;
 

fs/nfsd/vfs.c

@@ -1169,9 +1169,6 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	dentry = fhp->fh_dentry;
 	dirp = d_inode(dentry);
 
-	err = nfserr_notdir;
-	if (!dirp->i_op->lookup)
-		goto out;
 	/*
 	 * Check whether the response file handle has been verified yet.
 	 * If it has, the parent directory should already be locked.
@@ -1310,12 +1307,6 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	dentry = fhp->fh_dentry;
 	dirp = d_inode(dentry);
 
-	/* Get all the sanity checks out of the way before
-	 * we lock the parent. */
-	err = nfserr_notdir;
-	if (!dirp->i_op->lookup)
-		goto out;
-
 	host_err = fh_want_write(fhp);
 	if (host_err)
 		goto out_nfserr;