feat(chvt): use custom implementation instead of system()

Calling system() is vulnerable and shouldn't be used.

Makefile

@@ -10,10 +10,10 @@ ALLFLAGS=$(CFLAGS) -I$(IDIR)
 
 LIBS=-lm -lpam -lpam_misc
 
-_DEPS = util.h ui.h config.h auth.h efield.h keys.h users.h sessions.h
+_DEPS = util.h ui.h config.h auth.h efield.h keys.h users.h sessions.h chvt.h
 DEPS = $(patsubst %,$(IDIR)/%,$(_DEPS))
 
-_OBJ = main.o util.o ui.o config.o auth.o efield.o users.o sessions.o
+_OBJ = main.o util.o ui.o config.o auth.o efield.o users.o sessions.o chvt.o
 OBJ = $(patsubst %,$(ODIR)/%,$(_OBJ))
 
 $(ODIR)/%.o: $(CDIR)/%.c $(DEPS)

include/chvt.h

@@ -0,0 +1,21 @@
+#ifndef _CHVTH_
+#define _CHVTH_
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#define KDGKBTYPE 0x4b33
+#define VT_ACTIVATE 0x5606
+#define VT_WAITACTIVE 0x5607
+
+/**
+ * @brief change foreground virtual terminal to `n`
+ *
+ * @param n virtual terminal number
+ * @return int non-negative value on success
+ */
+int chvt(int n);
+
+#endif

src/chvt.c

@@ -0,0 +1,22 @@
+#include "chvt.h"
+
+static char *vterms[] = {"/dev/tty", "/dev/tty0", "/dev/vc/0", "/dev/systty",
+                         "/dev/console"};
+
+int chvt(int n) {
+  char c = 0;
+  for (int i = 0; i < sizeof(vterms) / sizeof(vterms[0]); i++) {
+    int fd = open(vterms[i], O_RDWR);
+    if (fd >= 0 && isatty(fd) && ioctl(fd, KDGKBTYPE, &c) == 0 && c < 3) {
+      if (ioctl(fd, VT_ACTIVATE, n) < 0 || ioctl(fd, VT_WAITACTIVE, n) < 0) {
+        printf("Couldn't active vt %d\n", n);
+        return -1;
+      }
+      return 0;
+    }
+    close(fd);
+  }
+
+  printf("Couldn't get a file descriptor referring to the console.\n");
+  return -1;
+}

src/main.c

@@ -4,22 +4,23 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#include <chvt.h>
 #include <config.h>
 #include <sessions.h>
 #include <ui.h>
 #include <users.h>
 
-void chvt(char *arg) {
+int chvt_char(char c) {
-  size_t bsize = snprintf(NULL, 0, "chvt %s", arg) + 1;
+  int i = c - '0';
-  char *buf = malloc(bsize);
+  if (i >= 0 && i <= 9) {
-  snprintf(buf, bsize, "chvt %s", arg);
+    return chvt(i);
-  system(buf);
+  }
-  free(buf);
+  return -1;
 }
 
 int main(int argc, char *argv[]) {
   if (argc == 2)
-    chvt(argv[1]);
+    chvt_char(argv[1][0]);
 
   struct config *config = parse_config("/etc/lidm.ini");
   if (config == NULL) {