From a7d9e1f93d278184a9804d27439056fc70cda3a4 Mon Sep 17 00:00:00 2001
From: simonb <simonb@NetBSD.org>
Date: Fri, 16 Jun 2000 00:20:23 +0000
Subject: [PATCH] Use new KERN_MSGBUF sysctl if running on a live kernel, and
 remove setgid kmem bit from executable.

---
 sbin/dmesg/dmesg.c | 98 +++++++++++++++++++++++++++++-----------------
 1 file changed, 61 insertions(+), 37 deletions(-)

diff --git a/sbin/dmesg/dmesg.c b/sbin/dmesg/dmesg.c
index 55465416b02a..268a3d3e7b20 100644
--- a/sbin/dmesg/dmesg.c
+++ b/sbin/dmesg/dmesg.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: dmesg.c,v 1.16 1998/07/05 08:56:54 mrg Exp $	*/
+/*	$NetBSD: dmesg.c,v 1.17 2000/06/16 00:20:23 simonb Exp $	*/
 /*-
  * Copyright (c) 1991, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -42,11 +42,13 @@ __COPYRIGHT("@(#) Copyright (c) 1991, 1993\n\
 #if 0
 static char sccsid[] = "@(#)dmesg.c	8.1 (Berkeley) 6/5/93";
 #else
-__RCSID("$NetBSD: dmesg.c,v 1.16 1998/07/05 08:56:54 mrg Exp $");
+__RCSID("$NetBSD: dmesg.c,v 1.17 2000/06/16 00:20:23 simonb Exp $");
 #endif
 #endif /* not lint */
 
+#include <sys/param.h>
 #include <sys/msgbuf.h>
+#include <sys/sysctl.h>
 
 #include <err.h>
 #include <fcntl.h>
@@ -54,7 +56,9 @@ __RCSID("$NetBSD: dmesg.c,v 1.16 1998/07/05 08:56:54 mrg Exp $");
 #include <limits.h>
 #include <nlist.h>
 #include <stdio.h>
+#include <stddef.h>
 #include <stdlib.h>
+#include <string.h>
 #include <time.h>
 #include <unistd.h>
 #include <vis.h>
@@ -76,11 +80,9 @@ main(argc, argv)
 	int argc;
 	char *argv[];
 {
+	struct kern_msgbuf cur;
 	int ch, newl, skip, i;
-	char *p;
-	struct kern_msgbuf *bufp, cur;
-	char *memf, *nlistf, *bufdata;
-	kvm_t *kd;
+	char *p, *memf, *nlistf, *bufdata;
 	char buf[5];
 
 	memf = nlistf = NULL;
@@ -99,38 +101,60 @@ main(argc, argv)
 	argc -= optind;
 	argv += optind;
 
-	/*
-	 * Discard setgid privileges if not the running kernel so that bad
-	 * guys can't print interesting stuff from kernel memory.
-	 */
-	if (memf != NULL || nlistf != NULL)
-		setgid(getgid());
+	if (memf == NULL && nlistf == NULL) {
+		size_t size;
+		int mib[2];
 
-	/* Read in message buffer header and data, and do sanity checks. */
-	if ((kd = kvm_open(nlistf, memf, NULL, O_RDONLY, "dmesg")) == NULL)
-		exit (1);
-	setgid(getgid());	/* do now anyway */
-	if (kvm_nlist(kd, nl) == -1)
-		errx(1, "kvm_nlist: %s", kvm_geterr(kd));
-	if (nl[X_MSGBUF].n_type == 0)
-		errx(1, "%s: msgbufp not found", nlistf ? nlistf : "namelist");
-	if (KREAD(nl[X_MSGBUF].n_value, bufp))
-		errx(1, "kvm_read: %s (0x%lx)", kvm_geterr(kd),
-		    nl[X_MSGBUF].n_value);
-	if (KREAD((long)bufp, cur))
-		errx(1, "kvm_read: %s (0x%lx)", kvm_geterr(kd),
-		    (unsigned long)bufp);
-	if (cur.msg_magic != MSG_MAGIC)
-		errx(1, "magic number incorrect");
-	bufdata = malloc(cur.msg_bufs);
-	if (bufdata == NULL)
-		errx(1, "couldn't allocate space for buffer data");
-	if (kvm_read(kd, (long)&bufp->msg_bufc, bufdata,
-	    cur.msg_bufs) != cur.msg_bufs)
-		errx(1, "kvm_read: %s", kvm_geterr(kd));
-	kvm_close(kd);
-	if (cur.msg_bufx >= cur.msg_bufs)
-		cur.msg_bufx = 0;
+		mib[0] = CTL_KERN;
+		mib[1] = KERN_MSGBUF;
+
+		if (sysctl(mib, 2, NULL, &size, NULL, 0) == -1)
+			errx(1, "can't get size of msgbuf");
+
+		if ((bufdata = malloc(size)) == NULL)
+			err(1, "couldn't allocate space for buffer data");
+
+		if (sysctl(mib, 2, bufdata, &size, NULL, 0) == -1)
+			err(1, "can't get msgbuf");
+
+		/* make a dummy struct msgbuf for the display logic */
+		cur.msg_bufx =  cur.msg_bufs = size;
+	} else {
+		kvm_t *kd;
+		struct kern_msgbuf *bufp;
+
+		/*
+		 * Read in message buffer header and data, and do sanity
+		 * checks.
+		 */
+		kd = kvm_open(nlistf, memf, NULL, O_RDONLY, "dmesg");
+		if (kd == NULL)
+			exit (1);
+		if (kvm_nlist(kd, nl) == -1)
+			errx(1, "kvm_nlist: %s", kvm_geterr(kd));
+		if (nl[X_MSGBUF].n_type == 0)
+			errx(1, "%s: msgbufp not found", nlistf ? nlistf :
+			    "namelist");
+		if (KREAD(nl[X_MSGBUF].n_value, bufp))
+			errx(1, "kvm_read: %s (0x%lx)", kvm_geterr(kd),
+			    nl[X_MSGBUF].n_value);
+		if (kvm_read(kd, (long)bufp, &cur,
+		    offsetof(struct kern_msgbuf, msg_bufc)) !=
+		    offsetof(struct kern_msgbuf, msg_bufc))
+			errx(1, "kvm_read: %s (0x%lx)", kvm_geterr(kd),
+			    (unsigned long)bufp);
+		if (cur.msg_magic != MSG_MAGIC)
+			errx(1, "magic number incorrect");
+		bufdata = malloc(cur.msg_bufs);
+		if (bufdata == NULL)
+			errx(1, "couldn't allocate space for buffer data");
+		if (kvm_read(kd, (long)&bufp->msg_bufc, bufdata,
+		    cur.msg_bufs) != cur.msg_bufs)
+			errx(1, "kvm_read: %s", kvm_geterr(kd));
+		kvm_close(kd);
+		if (cur.msg_bufx >= cur.msg_bufs)
+			cur.msg_bufx = 0;
+	}
 
 	/*
 	 * The message buffer is circular; start at the write pointer