From cbd712a43b8702517a1b4cbe50df6a0b8a39bae6 Mon Sep 17 00:00:00 2001
From: Jakob Kaivo <jkk@ungol.org>
Date: Wed, 1 Apr 2020 03:01:09 -0400
Subject: initial pass with some hard-coded values

---
 user.c | 164 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 163 insertions(+), 1 deletion(-)

diff --git a/user.c b/user.c
index 9a019a7..9eaa7e1 100644
--- a/user.c
+++ b/user.c
@@ -20,4 +20,166 @@
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
- */
\ No newline at end of file
+ */
+
+#define _POSIX_C_SOURCE 200809L
+#include <fcntl.h>
+#include <dirent.h>
+#include <pwd.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#define USERS_DIRECTORY "/var/secure/users"
+static DIR *users_dir = NULL;
+
+struct user {
+	struct passwd pw;
+	char *gecos;
+	char *password;
+};
+
+enum selection { UID, NAME, ALL };
+
+static struct user *user_read(char *name)
+{
+	static struct user u = { 0 };
+
+	int user = openat(dirfd(users_dir), name, O_SEARCH);
+	if (user == -1) {
+		return NULL;
+	}
+
+	struct stat st;
+	if (fstat(user, &st) != 0) {
+		close(user);
+		return NULL;
+	}
+
+	u.pw.pw_name = name;
+	u.pw.pw_uid = st.st_uid;
+	u.pw.pw_gid = st.st_gid;
+	u.pw.pw_dir = "/";	// TODO: read symlink at userfd, home
+	u.pw.pw_shell = "/bin/sh"; // TOOD: read symlink at userfd, shell
+	u.gecos = name;		// TODO: read file at userfd, gecos
+	u.password = "";	// TODO: read file at userfd, password
+
+	close(user);
+
+	return &u;
+}
+
+static char *user_uid(uid_t uid)
+{
+	char *name = NULL;
+
+	struct dirent *de;
+	while ((de = readdir(users_dir)) != NULL) {
+		if (!strcmp(de->d_name, ".") || !strcmp(de->d_name, "..")) {
+			continue;
+		}
+
+		struct stat st;
+		if (fstatat(dirfd(users_dir), de->d_name, &st, 0) != 0) {
+			continue;
+		}
+
+		if (st.st_uid == uid) {
+			name = de->d_name;
+			break;
+		}
+	}
+
+	return name;
+}
+
+static struct user *user_find(enum selection sel, char *name, uid_t uid)
+{
+	if (sel == UID) {
+		name = user_uid(uid);
+	}
+
+	return user_read(name);
+}
+
+static void user_print(const struct user *u)
+{
+	if (u == NULL) {
+		return;
+	}
+
+	printf("%s:%s:%jd:%jd:%s:%s:%s\n", u->pw.pw_name, u->password,
+		(intmax_t)u->pw.pw_uid, (intmax_t)u->pw.pw_gid,
+		u->gecos, u->pw.pw_dir, u->pw.pw_shell);
+}
+
+int main(int argc, char *argv[])
+{
+	char *name = getlogin();
+	uid_t uid = getuid();
+	enum selection sel = NAME;;
+	enum { LIST, PASSWORD } action = LIST;
+
+	int c;
+	while ((c = getopt(argc, argv, "LN:U:p")) != -1) {
+		switch (c) {
+		case 'L':
+			sel = ALL;
+			break;
+
+		case 'N':
+			sel = NAME;
+			name = optarg;
+			break;
+
+		case 'U':
+			sel = UID;
+			uid = atoi(optarg);
+			break;
+
+		case 'p':
+			action = PASSWORD;
+			break;
+
+		default:
+			return 1;
+		}
+	}
+
+	if (action == PASSWORD && sel == ALL) {
+		fprintf(stderr, "user: -L and -p are incompatible\n");
+		return 1;
+	}
+
+	users_dir = opendir(USERS_DIRECTORY);
+	if (users_dir == NULL) {
+		fprintf(stderr, "user: no users directory\n");
+		return 1;
+	}
+
+	if (action == PASSWORD) {
+		printf("TODO: interactively change password\n");
+		return 0;
+	}
+
+	if (sel == ALL) {
+		struct dirent *de = NULL;
+		while ((de = readdir(users_dir)) != NULL) {
+			if (!strcmp(de->d_name, ".") || !strcmp(de->d_name, "..")) {
+				continue;
+			}
+			user_print(user_read(de->d_name));
+		}
+		return 0;
+	}
+
+	struct user *u = user_find(sel, name, uid);
+	if (u == NULL) {
+		fprintf(stderr, "user: not found\n");
+		return 1;
+	}
+	user_print(u);
+}
-- 
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