Get rid of setgid kmem for systat, and while being there, fix some bugs

and compiler warnings.
The data for network statistics are still obtained via the kvm interface
if systat was started with the needed privileges, otherwise sysctls are
used. The reason for this is that with really many open sockets, the
sysctl method is probably slower, but it systat -netstat is probably not
really usable in either mode under these conditions.

Approved by:	rwatson

1 files changed, 25 insertions, 3 deletions

diff --git a/usr.bin/systat/main.c b/usr.bin/systat/main.c
index 52bb1e5..5678e41 100644
--- a/usr.bin/systat/main.c
+++ b/usr.bin/systat/main.c
@@ -47,6 +47,7 @@ static const char rcsid[] =
 
 #include <sys/param.h>
 #include <sys/time.h>
+#include <sys/sysctl.h>
 
 #include <err.h>
 #include <locale.h>
@@ -74,6 +75,7 @@ char    *namp;
 char    hostname[MAXHOSTNAMELEN];
 WINDOW  *wnd;
 int     CMDLINE;
+int     use_kvm = 1;
 
 static	WINDOW *wload;			/* one line window for load average */
 
@@ -82,7 +84,7 @@ main(argc, argv)
 	int argc;
 	char **argv;
 {
-	char errbuf[80];
+	char errbuf[80], dummy;
 	size_t	size;
 	int	err;
 
@@ -107,9 +109,29 @@ main(argc, argv)
 		argc--, argv++;
 	}
 	kd = kvm_openfiles(NULL, NULL, NULL, O_RDONLY, errbuf);
+	if (kd != NULL) {
+		/* 
+		 * Try to actually read something, we may be in a jail, and
+		 * have /dev/null opened as /dev/mem.
+		 */
+		if (kvm_nlist(kd, namelist) != 0 || namelist[0].n_value == 0 || 
+		    kvm_read(kd, namelist[0].n_value, &dummy, sizeof(dummy)) !=
+		    sizeof(dummy)) {
+			kvm_close(kd);
+			kd = NULL;
+		}
+	}
 	if (kd == NULL) {
-		error("%s", errbuf);
-		exit(1);
+		/* 
+		 * Maybe we are lacking permissions? Retry, this time with bogus
+		 * devices. We can now use sysctl only.
+		 */
+		use_kvm = 0;
+		kd = kvm_openfiles("/dev/null", "/dev/null", "/dev/null", O_RDONLY, errbuf);
+		if (kd == NULL) {
+			error("%s", errbuf);
+			exit(1);
+		}
 	}
 	signal(SIGINT, die);
 	signal(SIGQUIT, die);