Add su, add process group handling in shell

Makefile

@@ -21,7 +21,8 @@ STAGE_BIN=$(STAGE)/init \
 		  $(STAGE)/bin/rm \
 		  $(STAGE)/bin/mkdir \
 		  $(STAGE)/bin/login \
-		  $(STAGE)/bin/ase
+		  $(STAGE)/bin/ase \
+		  $(STAGE)/bin/su
 sh_OBJS=$(O)/sh/sh.o \
 		$(O)/sh/readline.o \
 		$(O)/sh/builtin.o \
@@ -45,6 +46,7 @@ clean:
 	rm -rf $(O)
 
 $(O)/initrd.img: mkstage-etc $(STAGE_BIN)
+	chmod 04711 $(STAGE)/bin/su
 	cd $(STAGE) && tar czf $(abspath $@) *
 
 mkdirs:

core/bin/login.c

@@ -1,4 +1,5 @@
 #include <string.h>
+#include <signal.h>
 #include <stdio.h>
 #include <errno.h>
 #include <pwd.h>
@@ -8,6 +9,9 @@ struct spwd {
     char *sp_pwdp;
 };
 
+static int attempt = 0;
+static char line_buf[64];
+
 static ssize_t getline(char *buf, size_t lim, char pwchr) {
     size_t c = 0;
     char chr;
@@ -124,6 +128,10 @@ static int loginas(const char *name) {
     return loginuid(res->pw_uid, res->pw_gid, shell);
 }
 
+static void signal_handler(int signum) {
+    // TODO: syscalls interruptible by singals
+}
+
 int main(int argc, char **argv) {
     // Arguments are ignored
     if (getuid() != 0) {
@@ -131,8 +139,8 @@ int main(int argc, char **argv) {
         return -1;
     }
 
-    int attempt = 0;
-    char line_buf[64];
+    signal(SIGINT, signal_handler);
+
     char spnam_buf[128];
     struct spwd sp;
 
@@ -162,10 +170,14 @@ int main(int argc, char **argv) {
             continue;
         }
 
-        printf("password: ");
-        if (getline(line_buf, sizeof(line_buf), '*') < 0) {
-            ++attempt;
-            continue;
+        if (sp.sp_pwdp[0] != 0) {
+            printf("password: ");
+            if (getline(line_buf, sizeof(line_buf), '*') < 0) {
+                ++attempt;
+                continue;
+            }
+        } else {
+            line_buf[0] = 0;
         }
 
         // No hashing yet, so just compare passwords
@@ -175,6 +187,7 @@ int main(int argc, char **argv) {
             attempt = 3;
             continue;
         } else {
+            printf("Login failed\n");
             ++attempt;
         }
     }

core/bin/ls.c

@@ -66,7 +66,7 @@ static int ls_dir(const char *path, int flags) {
                         t,
                         (ent_stat.st_mode & S_IRUSR) ? 'r' : '-',
                         (ent_stat.st_mode & S_IWUSR) ? 'w' : '-',
-                        (ent_stat.st_mode & S_IXUSR) ? 'x' : '-',
+                        (ent_stat.st_mode & S_ISUID ? 's' : (ent_stat.st_mode & S_IXUSR) ? 'x' : '-'),
                         (ent_stat.st_mode & S_IRGRP) ? 'r' : '-',
                         (ent_stat.st_mode & S_IWGRP) ? 'w' : '-',
                         (ent_stat.st_mode & S_IXGRP) ? 'x' : '-',

core/bin/su.c

@@ -0,0 +1,19 @@
+#include <stdio.h>
+
+int main(int argc, char **argv) {
+    if (getuid() != 0) {
+        printf("su binary must have setuid bit on\n");
+        return -1;
+    }
+
+    if (setgid(0) != 0) {
+        perror("setgid()");
+        return -1;
+    }
+
+    const char *shell = "/bin/sh";
+    const char *argp[] = {
+        shell, NULL
+    };
+    return execve(shell, argp, NULL);
+}

etc/shadow

@@ -1,2 +1,2 @@
 root:toor:
-alnyan:password:
+alnyan::

sh/cmd.c

@@ -1,3 +1,5 @@
+#include <sys/termios.h>
+#include <sys/ioctl.h>
 #include <string.h>
 #include <stdlib.h>
 #include <ctype.h>
@@ -57,11 +59,19 @@ static int cmd_spawn(const char *path, const struct cmd_exec *cmd, int *cmd_res)
     }
 
     if (pid == 0) {
+        pid = getpid();
+        ioctl(STDIN_FILENO, TIOCSPGRP, &pid);
+        setpgid(0, 0);
         exit(execve(path, (const char *const *) cmd->args, NULL));
     } else {
         if (waitpid(pid, cmd_res) != 0) {
             perror("waitpid()");
         }
+
+        // Regain control of foreground group
+        pid = getpgid(0);
+        ioctl(STDIN_FILENO, TIOCSPGRP, &pid);
+
         return 0;
     }
 }

sh/sh.c

@@ -1,3 +1,4 @@
+#include <signal.h>
 #include <string.h>
 #include <stdio.h>
 #include <pwd.h>
@@ -72,11 +73,17 @@ static void display_prompt(void) {
     }
 }
 
+static void signal_handle(int signum) {
+    printf("\n^C\n");
+}
+
 int main(int argc, char **argv) {
     int fd = STDIN_FILENO;
     char linebuf[256];
     int res;
 
+    signal(SIGINT, signal_handle);
+
     if (argc == 2) {
         fd = open(argv[1], O_RDONLY, 0);