bug#37344: rcirc: nil gets interpreted as a nickname

[Leo Liu]

On 2019-09-08 20:58 +0200, Naïm Favier wrote:
> Severity: normal
>
> Ever since I changed my nickname to "nil" on Freenode, I've been
> getting occasional private messages from unknown users consisting of a
> single empty CTCP ACTION. After a bit of investigating, it turned out
> they all used rcirc. The situation was clear at that point: somewhere
> in rcirc's source code, a nil value is being implicitly converted to a
> string and used as the target of a PRIVMSG command.
>
> The bug seems to be reproducible by issuing "/me" (without arguments)
> inside a server buffer: the "nil" user on that server gets sent an
> empty ACTION.
>
> Suggested fix: in rcirc-send-privmsg, fail if target is nil. It might
> be useful to check other places where the "%s" format is used, to
> discover similar bugs.

Thanks. Does the following patch fix the issue?

diff --git a/lisp/net/rcirc.el b/lisp/net/rcirc.el
index de524d9e..d95db26c 100644
--- a/lisp/net/rcirc.el
+++ b/lisp/net/rcirc.el
@@ -825,6 +825,7 @@ Function is called with PROCESS, COMMAND, SENDER, ARGS and 
LINE.")
     (process-send-string process string)))
 
 (defun rcirc-send-privmsg (process target string)
+  (cl-check-type target string)
   (rcirc-send-string process (format "PRIVMSG %s :%s" target string)))
 
 (defun rcirc-send-ctcp (process target request &optional args)
@@ -2337,8 +2338,8 @@ With a prefix arg, prompt for new topic."
   (let ((timestamp (format-time-string "%s")))
     (rcirc-send-ctcp process target "PING" timestamp)))
 
-(defun rcirc-cmd-me (args &optional process target)
-  (rcirc-send-ctcp process target "ACTION" args))
+(defun rcirc-cmd-me (args process target)
+  (when target (rcirc-send-ctcp process target "ACTION" args)))
 
 (defun rcirc-add-or-remove (set &rest elements)
   (dolist (elt elements)