From 5412a3785eb9293c98f28431ba00ca262bb3479f Mon Sep 17 00:00:00 2001
From: Alessandro Mauri <alemauri001@gmail.com>
Date: Sun, 4 Apr 2021 12:42:03 +0200
Subject: [PATCH] change env

us now changes the environment variables listed in TODO before executing the
command, also added but commented out a version where the env gets copied and
the execution happens trough the musl implementation of execvpe(3)
---
 us.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 68 insertions(+), 2 deletions(-)

diff --git a/us.c b/us.c
index 09778b2..69db7a7 100644
--- a/us.c
+++ b/us.c
@@ -36,6 +36,7 @@ static int perm_set (struct passwd *, struct group *);
 static int authenticate (const char *);
 static struct passwd* user_to_passwd (const char *);
 static struct group* group_to_grp (const char *);
+//static int execvpe(const char *, char *const *, char *const *);
 
 // FIXME: misc_conv is a separate library, should stick to plain PAM or make
 // our own pam module
@@ -48,7 +49,7 @@ int main (int argc, char *argv[])
 	char *t_usr = "root", *t_grp = NULL;
 	struct passwd *t_pw;
 	struct group *t_gr;
-	int opt;
+	int opt, err;
 	int shellflag = 0;
 	while ((opt = getopt(argc, argv, "A:u:g:C:s")) != -1) {
 		switch (opt) {
@@ -134,10 +135,37 @@ int main (int argc, char *argv[])
 	c_argv[c_argc] = NULL;
 
 	/* Authenticate */
+	// FIXME: move this up
 	if (authenticate(uname) != PAM_SUCCESS)
 		exit(EXIT_FAILURE);
 
 	// TODO: clean up env
+	/* copy and filter env */
+/*
+	char **c_env;
+	extern char **environ;
+	int size = 0;
+	for (int i = 0; environ[i]; i++, size++);
+	c_env = malloc(sizeof(char *) * (size + 1));
+	if (!c_env) {
+		fprintf(stderr, "malloc: %s\n", strerror(errno));
+		exit(errno);
+	}
+	for (int i = 0; environ[i]; i++) {
+		c_env[i] = strdup(environ[i]);
+		if (!c_env[i]) {
+			fprintf(stderr, "strdup: %s\n", strerror(errno));
+			exit(errno);
+		}
+	}
+	c_env[size] = NULL;
+*/
+	// TODO: check err value
+	// TODO: add all this to list and loop over it
+	err = setenv("USER", t_pw->pw_name, 1);
+	err = setenv("LOGNAME", t_pw->pw_name, 1);
+	err = setenv("SHELL", t_pw->pw_shell, 1);
+	err = setenv("HOME", t_pw->pw_dir, 1);
 
 	errno = 0;
 	/* Set permissions */
@@ -147,7 +175,6 @@ int main (int argc, char *argv[])
 	}
 
 	/* Execute the command */
-	int err;
 	err = execvp(c_argv[0], c_argv);
 	if (err == -1)
 		fprintf(stderr, "execl: %s\n", strerror(errno));
@@ -305,3 +332,42 @@ static struct group* group_to_grp (const char *group)
 	}
 	return gr;
 }
+
+/*
+static int execvpe(const char *file, char *const argv[], char *const envp[])
+{
+	const char *p, *z, *path = getenv("PATH");
+	size_t l, k;
+
+	errno = ENOENT;
+	if (!*file) return -1;
+
+	if (strchr(file, '/'))
+		return execve(file, argv, envp);
+
+	if (!path) path = "/usr/local/bin:/bin:/usr/bin";
+	k = strnlen(file, NAME_MAX+1);
+	if (k > NAME_MAX) {
+		errno = ENAMETOOLONG;
+		return -1;
+	}
+	l = strnlen(path, PATH_MAX-1)+1;
+
+	for(p=path; ; p=z) {
+		char b[l+k+1];
+		z = strchr(p, ':');
+		if (!z) z = p+strlen(p);
+		if ((size_t)(z-p) >= l) {
+			if (!*z++) break;
+			continue;
+		}
+		memcpy(b, p, z-p);
+		b[z-p] = '/';
+		memcpy(b+(z-p)+(z>p), file, k+1);
+		execve(b, argv, envp);
+		if (errno != ENOENT) return -1;
+		if (!*z++) break;
+	}
+	return -1;
+}
+*/