Disable tracing on FreeBSD using procctl. (OpenSSH Portable 8.8)

[Darren Tucker]

On Sun, Nov 06, 2022 at 09:34:05AM -0500, Ed Maste wrote:
> On Sat, 5 Nov 2022 at 21:02, Darren Tucker <dtucker at dtucker.net> wrote:
> >
> > Maybe it should try the "0" version, then if that fails try the
> > getpid() version and only then fail if "strict" is set?
> 
> Ah, yes that sounds like the way to do it, and with no extra overhead
> for the usual (recent kernel) case. Something like this?

I had something similar but a bit more compact and commented.  Does this
also work?

diff --git a/platform-tracing.c b/platform-tracing.c
index c2810f2d..a8ce078b 100644
--- a/platform-tracing.c
+++ b/platform-tracing.c
@@ -32,6 +32,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
+#include <unistd.h>
 
 #include "log.h"
 
@@ -39,10 +40,16 @@ void
 platform_disable_tracing(int strict)
 {
 #if defined(HAVE_PROCCTL) && defined(PROC_TRACE_CTL)
-	/* On FreeBSD, we should make this process untraceable */
+	/*
+	 * On FreeBSD, we should make this process untraceable.
+	 * pid=0 means "this process" and but some older kernels do not
+	 * understand that, so retry with our own pid before failing.
+	 */
 	int disable_trace = PROC_TRACE_CTL_DISABLE;
 
-	if (procctl(P_PID, 0, PROC_TRACE_CTL, &disable_trace) && strict)
+	if (procctl(P_PID, 0, PROC_TRACE_CTL, &disable_trace) == -1 &&
+	    procctl(P_PID, getpid(), PROC_TRACE_CTL, &disable_trace) == -1 &&
+	    strict)
 		fatal("unable to make the process untraceable: %s",
 		    strerror(errno));
 #endif

-- 
Darren Tucker (dtucker at dtucker.net)
GPG key 11EAA6FA / A86E 3E07 5B19 5880 E860  37F4 9357 ECEF 11EA A6FA (new)
    Good judgement comes with experience. Unfortunately, the experience
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