svn commit: r202692 - in head/sys: kern sys

[Konstantin Belousov]

Author: kib
Date: Wed Jan 20 11:58:04 2010
New Revision: 202692
URL: http://svn.freebsd.org/changeset/base/202692

Log:
  When traced process is about to receive the signal, the process is
  stopped and debugger may modify or drop the signal. After the changes to
  keep process-targeted signals on the process sigqueue, another thread
  may note the old signal on the queue and act before the thread removes
  changed or dropped signal from the process queue. Since process is
  traced, it usually gets stopped. Or, if the same signal is delivered
  while process was stopped, the thread may erronously remove it,
  intending to remove the original signal.
  
  Remove the signal from the queue before notifying the debugger. Restore
  the siginfo to the head of sigqueue when signal is allowed to be
  delivered to the debugee, using newly introduced KSI_HEAD ksiginfo_t
  flag. This preserves required order of delivery. Always restore the
  unchanged signal on the curthread sigqueue, not to the process queue,
  since the thread is about to get it anyway, because sigmask cannot be
  changed.
  
  Handle failure of reinserting the siginfo into the queue by falling
  back to sq_kill method, calling sigqueue_add with NULL ksi.
  
  If debugger changed the signal to be delivered, use sigqueue_add()
  with NULL ksi instead of only setting sq_signals bit.
  
  Reported by:	Gardner Bell <gbell72 rogers com>
  Analyzed and first version of fix by:	Tijl Coosemans <tijl coosemans org>
  PR:	142757
  Reviewed by:	davidxu
  MFC after:	2 weeks

Modified:
  head/sys/kern/kern_sig.c
  head/sys/sys/signalvar.h

Modified: head/sys/kern/kern_sig.c
==============================================================================
--- head/sys/kern/kern_sig.c	Wed Jan 20 11:55:14 2010	(r202691)
+++ head/sys/kern/kern_sig.c	Wed Jan 20 11:58:04 2010	(r202692)
@@ -357,7 +357,10 @@ sigqueue_add(sigqueue_t *sq, int signo, 
 
 	/* directly insert the ksi, don't copy it */
 	if (si->ksi_flags & KSI_INS) {
-		TAILQ_INSERT_TAIL(&sq->sq_list, si, ksi_link);
+		if (si->ksi_flags & KSI_HEAD)
+			TAILQ_INSERT_HEAD(&sq->sq_list, si, ksi_link);
+		else
+			TAILQ_INSERT_TAIL(&sq->sq_list, si, ksi_link);
 		si->ksi_sigq = sq;
 		goto out_set_bit;
 	}
@@ -378,7 +381,10 @@ sigqueue_add(sigqueue_t *sq, int signo, 
 			p->p_pendingcnt++;
 		ksiginfo_copy(si, ksi);
 		ksi->ksi_signo = signo;
-		TAILQ_INSERT_TAIL(&sq->sq_list, ksi, ksi_link);
+		if (si->ksi_flags & KSI_HEAD)
+			TAILQ_INSERT_HEAD(&sq->sq_list, ksi, ksi_link);
+		else
+			TAILQ_INSERT_TAIL(&sq->sq_list, ksi, ksi_link);
 		ksi->ksi_sigq = sq;
 	}
 
@@ -2492,6 +2498,7 @@ issignal(struct thread *td, int stop_all
 	struct sigacts *ps;
 	struct sigqueue *queue;
 	sigset_t sigpending;
+	ksiginfo_t ksi;
 	int sig, prop, newsig;
 
 	p = td->td_proc;
@@ -2529,24 +2536,22 @@ issignal(struct thread *td, int stop_all
 		if (p->p_flag & P_TRACED && (p->p_flag & P_PPWAIT) == 0) {
 			/*
 			 * If traced, always stop.
+			 * Remove old signal from queue before the stop.
+			 * XXX shrug off debugger, it causes siginfo to
+			 * be thrown away.
 			 */
+			queue = &td->td_sigqueue;
+			ksi.ksi_signo = 0;
+			if (sigqueue_get(queue, sig, &ksi) == 0) {
+				queue = &p->p_sigqueue;
+				sigqueue_get(queue, sig, &ksi);
+			}
+
 			mtx_unlock(&ps->ps_mtx);
 			newsig = ptracestop(td, sig);
 			mtx_lock(&ps->ps_mtx);
 
 			if (sig != newsig) {
-				ksiginfo_t ksi;
-
-				queue = &td->td_sigqueue;
-				/*
-				 * clear old signal.
-				 * XXX shrug off debugger, it causes siginfo to
-				 * be thrown away.
-				 */
-				if (sigqueue_get(queue, sig, &ksi) == 0) {
-					queue = &p->p_sigqueue;
-					sigqueue_get(queue, sig, &ksi);
-				}
 
 				/*
 				 * If parent wants us to take the signal,
@@ -2561,10 +2566,20 @@ issignal(struct thread *td, int stop_all
 				 * Put the new signal into td_sigqueue. If the
 				 * signal is being masked, look for other signals.
 				 */
-				SIGADDSET(queue->sq_signals, sig);
+				sigqueue_add(queue, sig, NULL);
 				if (SIGISMEMBER(td->td_sigmask, sig))
 					continue;
 				signotify(td);
+			} else {
+				if (ksi.ksi_signo != 0) {
+					ksi.ksi_flags |= KSI_HEAD;
+					if (sigqueue_add(&td->td_sigqueue, sig,
+					    &ksi) != 0)
+						ksi.ksi_signo = 0;
+				}
+				if (ksi.ksi_signo == 0)
+					sigqueue_add(&td->td_sigqueue, sig,
+					    NULL);
 			}
 
 			/*

Modified: head/sys/sys/signalvar.h
==============================================================================
--- head/sys/sys/signalvar.h	Wed Jan 20 11:55:14 2010	(r202691)
+++ head/sys/sys/signalvar.h	Wed Jan 20 11:58:04 2010	(r202692)
@@ -234,6 +234,7 @@ typedef struct ksiginfo {
 #define	KSI_EXT		0x02	/* Externally managed ksi. */
 #define KSI_INS		0x04	/* Directly insert ksi, not the copy */
 #define	KSI_SIGQ	0x08	/* Generated by sigqueue, might ret EGAIN. */
+#define	KSI_HEAD	0x10	/* Insert into head, not tail. */
 #define	KSI_COPYMASK	(KSI_TRAP|KSI_SIGQ)
 
 #define	KSI_ONQ(ksi)	((ksi)->ksi_sigq != NULL)