Fix long standing bug that prevents the PT_CONTINUE, PT_KILL and

PT_DETACH ptrace(2) requests from functioning as advertised in the
manual page.  As described in kern/35175, the PT_DETACH request will,
under certain circumstances, pass an unwanted signal on to the traced
process upan detaching from it.  The PT_CONTINUE request will
sometimes fail if you make it pass a signal that has "properties" that
differ from the properties of the signal that origionally caused the
traced process to be stopped.  Since PT_KILL is nothing than
PT_CONTINUE with SIGKILL, it is broken too.  In the PT_KILL case, this
leads to an unkillable process.

PR:		44011
Submitted by:	Mark Kettenis <kettenis@chello.nl>
Approved by:	re(jhb)

1 files changed, 10 insertions, 9 deletions

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index abe10df..ef4948f 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -1917,7 +1917,6 @@ issignal(td)
 		if (SIGISEMPTY(sigpending))	/* no signal to send */
 			return (0);
 		sig = sig_ffs(&sigpending);
-		prop = sigprop(sig);
 
 		_STOPEVENT(p, S_SIG, sig);
 
@@ -1953,14 +1952,6 @@ issignal(td)
 			mtx_lock(&ps->ps_mtx);
 
 			/*
-			 * If the traced bit got turned off, go back up
-			 * to the top to rescan signals.  This ensures
-			 * that p_sig* and p_sigacts are consistent.
-			 */
-			if ((p->p_flag & P_TRACED) == 0)
-				continue;
-
-			/*
 			 * If parent wants us to take the signal,
 			 * then it will leave it in p->p_xstat;
 			 * otherwise we just look for signals again.
@@ -1971,6 +1962,14 @@ issignal(td)
 				continue;
 
 			/*
+			 * If the traced bit got turned off, go back up
+			 * to the top to rescan signals.  This ensures
+			 * that p_sig* and p_sigact are consistent.
+			 */
+			if ((p->p_flag & P_TRACED) == 0)
+				continue;
+
+			/*
 			 * Put the new signal into td_siglist.  If the
 			 * signal is being masked, look for other signals.
 			 */
@@ -1980,6 +1979,8 @@ issignal(td)
 			signotify(td);
 		}
 
+		prop = sigprop(sig);
+
 		/*
 		 * Decide whether the signal should be returned.
 		 * Return the signal's number, or fall through