2 * A simple gateway for set-uid scripts
4 * (c) 2013 Martin Mares <mj@ucw.cz>
24 #define NONRET __attribute__((noreturn))
25 #define UNUSED __attribute__((unused))
28 #define DBG(...) printf(__VA_ARGS__)
30 #define DBG(...) do { } while (0)
33 static char program_name[PATH_MAX];
34 static char script_path[PATH_MAX];
38 static const char * const script_dirs[] = {
39 "/usr/local/lib/suidgw",
47 static char env_orig_uid[32], env_orig_gid[32];
49 static char *sanitized_env[] = {
50 "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
56 static void NONRET die(const char *fmt, ...)
60 fprintf(stderr, "suidgw: ");
61 vfprintf(stderr, fmt, args);
66 static void sanitize_fds(void)
68 // Make sure that nobody is playing dirty games with our file descriptors
72 fd = open("/dev/null", O_RDWR);
74 die("Cannot open /dev/null: %m");
80 static void sanitize_env(void)
82 snprintf(env_orig_uid, sizeof(env_orig_uid), "ORIG_UID=%d", (int) getuid());
83 snprintf(env_orig_gid, sizeof(env_orig_gid), "ORIG_GID=%d", (int) getgid());
86 static bool get_program_name(const char *arg0)
88 // If arg0 is a path, extract the last component
89 const char *p = strrchr(arg0, '/');
95 // Reject empty and oversized names
96 if (!p[0] || strlen(p) >= PATH_MAX)
99 // Reject invalid characters
100 for (const char *q = p; *q; q++)
103 if (! (c >= 'a' && c <= 'z' ||
104 c >= 'A' && c <= 'Z' ||
105 c >= '0' && c <= '9' ||
111 DBG("Program name: <%s>\n", p);
112 strcpy(program_name, p);
116 static void find_script(void)
118 for (int i = 0; script_dirs[i]; i++)
120 int len = snprintf(script_path, PATH_MAX, "%s/%s", script_dirs[i], program_name);
123 DBG("Trying <%s>\n", script_path);
124 if (access(script_path, X_OK) >= 0)
126 DBG("Found <%s>\n", script_path);
130 die("Cannot run %s: %m", script_path);
133 die("Unable to find script %s", program_name);
136 static void check_stat(void)
139 if (stat(script_path, &st) < 0)
140 die("Cannot stat %s: %m", script_path);
142 if (!S_ISREG(st.st_mode))
143 die("Not a regular file: %s", script_path);
144 if (!(st.st_mode & (S_ISUID | S_ISGID)))
145 die("Missing suid/sgid: %s", script_path);
147 use_uid = (st.st_mode & S_ISUID) ? st.st_uid : getuid();
148 use_gid = (st.st_mode & S_ISGID) ? st.st_gid : getgid();
149 DBG("Will use uid=%d gid=%d\n", (int) use_uid, (int) use_gid);
152 static void switch_ugid(void)
154 if (setresgid(use_gid, use_gid, use_gid) < 0)
155 die("Failed to set group id: %m");
157 if (setresuid(use_uid, use_uid, use_uid) < 0)
158 die("Failed to set user id: %m");
161 int main(int argc UNUSED, char **argv)
167 die("Must be run setuid");
169 struct passwd *pwd = getpwuid(getuid());
171 die("You don't exist");
173 openlog("suidgw", LOG_NDELAY | LOG_PID, LOG_AUTH);
175 if (!get_program_name(argv[0]))
176 die("Unable to parse program name %s", argv[0]);
182 syslog(LOG_INFO, "User %s executes %s with uid=%d, gid=%d",
183 pwd->pw_name, script_path, (int) use_uid, (int) use_gid);
185 if (execve(script_path, argv, sanitized_env) < 0)
186 die("Cannot execute %s: %m", script_path);
188 die("This must never happen");