cifs: Check for existing directory when opening file with O_CREAT

commit 8d9535b6 upstream.

When opening a file with O_CREAT flag, check to see if the file opened
is an existing directory.

This prevents the directory from being opened which subsequently causes
a crash when the close function for directories cifs_closedir() is called
which frees up the file->private_data memory while the file is still
listed on the open file list for the tcon.
Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Reported-by: Xiaoli Feng <xifeng@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/cifs/dir.c

@@ -229,6 +229,13 @@ cifs_do_create(struct inode *inode, struct dentry *direntry, unsigned int xid,
 				goto cifs_create_get_file_info;
 			}
 
+			if (S_ISDIR(newinode->i_mode)) {
+				CIFSSMBClose(xid, tcon, fid->netfid);
+				iput(newinode);
+				rc = -EISDIR;
+				goto out;
+			}
+
 			if (!S_ISREG(newinode->i_mode)) {
 				/*
 				 * The server may allow us to open things like
@@ -399,10 +406,14 @@ cifs_do_create(struct inode *inode, struct dentry *direntry, unsigned int xid,
 	if (rc != 0) {
 		cifs_dbg(FYI, "Create worked, get_inode_info failed rc = %d\n",
 			 rc);
-		if (server->ops->close)
-			server->ops->close(xid, tcon, fid);
-		goto out;
+		goto out_err;
 	}
+
+	if (S_ISDIR(newinode->i_mode)) {
+		rc = -EISDIR;
+		goto out_err;
+	}
+
 	d_drop(direntry);
 	d_add(direntry, newinode);
 
@@ -410,6 +421,13 @@ cifs_do_create(struct inode *inode, struct dentry *direntry, unsigned int xid,
 	kfree(buf);
 	kfree(full_path);
 	return rc;
+
+out_err:
+	if (server->ops->close)
+		server->ops->close(xid, tcon, fid);
+	if (newinode)
+		iput(newinode);
+	goto out;
 }
 
 int