From abe3a10852489c9ab16d32dc2902d399e40b7c2f Mon Sep 17 00:00:00 2001
From: art <art@openbsd.org>
Date: Thu, 20 Apr 2000 10:03:41 +0000
Subject: [PATCH] Add a function "ktrsettracevnode", that changes the ktrace
 vnode for a process in a correct way. Use it in all places where the vnode
 was changed. (most of the earlier code was incorrect and had races).

---
 sys/kern/kern_exec.c   |  5 ++---
 sys/kern/kern_exit.c   |  5 +++--
 sys/kern/kern_ktrace.c | 46 +++++++++++++++++++++++++-----------------
 sys/sys/ktrace.h       |  4 +++-
 4 files changed, 36 insertions(+), 24 deletions(-)

diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index 15ed8af28fe..b5de0c02c0d 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_exec.c,v 1.41 2000/03/23 15:55:52 art Exp $	*/
+/*	$OpenBSD: kern_exec.c,v 1.42 2000/04/20 10:03:42 art Exp $	*/
 /*	$NetBSD: kern_exec.c,v 1.75 1996/02/09 18:59:28 christos Exp $	*/
 
 /*-
@@ -497,8 +497,7 @@ sys_execve(p, v, retval)
 		 */
 		if (p->p_tracep && !(p->p_traceflag & KTRFAC_ROOT)) {
 			p->p_traceflag = 0;
-			vrele(p->p_tracep);
-			p->p_tracep = NULL;
+			ktrsettracevnode(p, NULL);
 		}
 #endif
 		p->p_ucred = crcopy(cred);
diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 5efdeea121a..97a98643f58 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_exit.c,v 1.22 2000/03/23 15:55:52 art Exp $	*/
+/*	$OpenBSD: kern_exit.c,v 1.23 2000/04/20 10:03:43 art Exp $	*/
 /*	$NetBSD: kern_exit.c,v 1.39 1996/04/22 01:38:25 christos Exp $	*/
 
 /*
@@ -63,6 +63,7 @@
 #include <sys/filedesc.h>
 #include <sys/signalvar.h>
 #include <sys/sched.h>
+#include <sys/ktrace.h>
 #ifdef SYSVSHM
 #include <sys/shm.h>
 #endif
@@ -210,7 +211,7 @@ exit1(p, rv)
 	 */
 	p->p_traceflag = 0;	/* don't trace the vrele() */
 	if (p->p_tracep)
-		vrele(p->p_tracep);
+		ktrsettracevnode(p, NULL);
 #endif
 	/*
 	 * Remove proc from allproc queue and pidhash chain.
diff --git a/sys/kern/kern_ktrace.c b/sys/kern/kern_ktrace.c
index 77d4b6b7bf5..240d13c8fb1 100644
--- a/sys/kern/kern_ktrace.c
+++ b/sys/kern/kern_ktrace.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_ktrace.c,v 1.17 2000/04/19 10:56:41 art Exp $	*/
+/*	$OpenBSD: kern_ktrace.c,v 1.18 2000/04/20 10:03:42 art Exp $	*/
 /*	$NetBSD: kern_ktrace.c,v 1.23 1996/02/09 18:59:36 christos Exp $	*/
 
 /*
@@ -60,6 +60,29 @@ int ktrsetchildren __P((struct proc *, struct proc *, int, int,
 int ktrwrite __P((struct vnode *, struct ktr_header *));
 int ktrcanset __P((struct proc *, struct proc *));
 
+/*
+ * Change the trace vnode in a correct way (to avoid races).
+ */
+void
+ktrsettracevnode(p, newvp)
+	struct proc *p;
+	struct vnode *newvp;
+{
+	struct vnode *vp;
+
+	if (p->p_tracep == newvp)	/* avoid work */
+		return;
+
+	if (newvp != NULL)
+		VREF(newvp);
+
+	vp = p->p_tracep;
+	p->p_tracep = newvp;
+
+	if (vp != NULL)
+		vrele(vp);
+}
+
 void
 ktrinitheader(kth, p, type)
 	struct ktr_header *kth;
@@ -324,9 +347,8 @@ sys_ktrace(curp, v, retval)
 		for (p = LIST_FIRST(&allproc); p; p = LIST_NEXT(p, p_list)) {
 			if (p->p_tracep == vp) {
 				if (ktrcanset(curp, p)) {
-					p->p_tracep = NULL;
 					p->p_traceflag = 0;
-				        vrele(vp);
+					ktrsettracevnode(p, NULL);
 				} else
 					error = EPERM;
 			}
@@ -391,15 +413,7 @@ ktrops(curp, p, ops, facs, vp)
 	if (!ktrcanset(curp, p))
 		return (0);
 	if (ops == KTROP_SET) {
-		if (p->p_tracep != vp) { 
-			/*
-			 * if trace file already in use, relinquish
-			 */
-			if (p->p_tracep != NULL)
-				vrele(p->p_tracep);
-			VREF(vp);
-			p->p_tracep = vp;
-		}
+		ktrsettracevnode(p, vp);
 		p->p_traceflag |= facs;
 		if (curp->p_ucred->cr_uid == 0)
 			p->p_traceflag |= KTRFAC_ROOT;
@@ -408,10 +422,7 @@ ktrops(curp, p, ops, facs, vp)
 		if (((p->p_traceflag &= ~facs) & KTRFAC_MASK) == 0) {
 			/* no more tracing */
 			p->p_traceflag = 0;
-			if (p->p_tracep != NULL) {
-				vrele(p->p_tracep);
-				p->p_tracep = NULL;
-			}
+			ktrsettracevnode(p, NULL);
 		}
 	}
 
@@ -496,9 +507,8 @@ ktrwrite(vp, kth)
 	    error);
 	for (p = LIST_FIRST(&allproc); p != NULL; p = LIST_NEXT(p, p_list)) {
 		if (p->p_tracep == vp) {
-			p->p_tracep = NULL;
 			p->p_traceflag = 0;
-			vrele(vp);
+			ktrsettracevnode(p, NULL);
 		}
 	}
 
diff --git a/sys/sys/ktrace.h b/sys/sys/ktrace.h
index 83e1f7dd30c..2fc4b4b368a 100644
--- a/sys/sys/ktrace.h
+++ b/sys/sys/ktrace.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ktrace.h,v 1.2 1996/03/03 12:11:54 niklas Exp $	*/
+/*	$OpenBSD: ktrace.h,v 1.3 2000/04/20 10:03:41 art Exp $	*/
 /*	$NetBSD: ktrace.h,v 1.12 1996/02/04 02:12:29 christos Exp $	*/
 
 /*
@@ -173,4 +173,6 @@ void ktrpsig __P((struct vnode *, int, sig_t, int, int));
 void ktrsyscall __P((struct vnode *, register_t, size_t, register_t []));
 void ktrsysret __P((struct vnode *, register_t, int, register_t));
 
+void ktrsettracevnode __P((struct proc *, struct vnode *));
+
 #endif	/* !_KERNEL */
-- 
2.20.1