From: Scott Cheloha <scottcheloha@gmail.com>
Subject: Re: pthread_mutex_timedlock(3): don't block forever if the timeout is NULL
To: tech@openbsd.org
Date: Sat, 27 Jan 2024 18:19:59 -0600

On Tue, Jan 09, 2024 at 11:14:08PM -0600, Scott Cheloha wrote:
> Both pthread_mutex_timedlock(3) implementations pass the timeout
> parameter from the caller through to the internal implementation
> function.  In both of those functions, a NULL timeout pointer means
> "no timeout" or "block indefinitely".
> 
> So, we have accidentally extended the pthread_mutex_timedlock(3)
> specification with special, undocumented behavior when the timeout
> pointer is NULL.
> 
> The easy fix is to copy the timeout to the stack before passing it on.
> 
> This change will cause any code that depends upon the current behavior
> to segfault instead of blocking indefinitely.  I think it's unlikely
> such code exists.  It it does exist, it is not portable.
> 
> ok?

Ping.

Index: rthread_mutex.c
===================================================================
RCS file: /cvs/src/lib/libc/thread/rthread_mutex.c,v
diff -u -p -r1.5 rthread_mutex.c
--- rthread_mutex.c	13 Feb 2019 13:09:32 -0000	1.5
+++ rthread_mutex.c	28 Jan 2024 00:19:09 -0000
@@ -211,9 +211,11 @@ pthread_mutex_trylock(pthread_mutex_t *m
 }
 
 int
-pthread_mutex_timedlock(pthread_mutex_t *mutexp, const struct timespec *abs)
+pthread_mutex_timedlock(pthread_mutex_t *mutexp, const struct timespec *absp)
 {
-	return (_rthread_mutex_timedlock(mutexp, 0, abs, 1));
+	struct timespec abs = *absp;
+
+	return (_rthread_mutex_timedlock(mutexp, 0, &abs, 1));
 }
 
 int
Index: rthread_sync.c
===================================================================
RCS file: /cvs/src/lib/libc/thread/rthread_sync.c,v
diff -u -p -r1.6 rthread_sync.c
--- rthread_sync.c	10 Jan 2024 04:28:43 -0000	1.6
+++ rthread_sync.c	28 Jan 2024 00:19:09 -0000
@@ -179,9 +179,11 @@ pthread_mutex_trylock(pthread_mutex_t *p
 }
 
 int
-pthread_mutex_timedlock(pthread_mutex_t *p, const struct timespec *abstime)
+pthread_mutex_timedlock(pthread_mutex_t *p, const struct timespec *abstimep)
 {
-	return (_rthread_mutex_lock(p, 0, abstime));
+	struct timespec abstime = *abstimep;
+
+	return (_rthread_mutex_lock(p, 0, &abstime));
 }
 
 int