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 *sanitized_env[] = {
48 "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
52 static void NONRET die(const char *fmt, ...)
56 fprintf(stderr, "suidgw: ");
57 vfprintf(stderr, fmt, args);
62 static void sanitize_fds(void)
64 // Make sure that nobody is playing dirty games with our file descriptors
68 fd = open("/dev/null", O_RDWR);
70 die("Cannot open /dev/null: %m");
76 static bool get_program_name(const char *arg0)
78 // If arg0 is a path, extract the last component
79 const char *p = strrchr(arg0, '/');
85 // Reject empty and oversized names
86 if (!p[0] || strlen(p) >= PATH_MAX)
89 // Reject invalid characters
90 for (const char *q = p; *q; q++)
93 if (! (c >= 'a' && c <= 'z' ||
94 c >= 'A' && c <= 'Z' ||
95 c >= '0' && c <= '9' ||
101 DBG("Program name: <%s>\n", p);
102 strcpy(program_name, p);
106 static void find_script(void)
108 for (int i = 0; script_dirs[i]; i++)
110 int len = snprintf(script_path, PATH_MAX, "%s/%s", script_dirs[i], program_name);
113 DBG("Trying <%s>\n", script_path);
114 if (access(script_path, X_OK) >= 0)
116 DBG("Found <%s>\n", script_path);
120 die("Cannot run %s: %m", script_path);
123 die("Unable to find script %s", program_name);
126 static void check_stat(void)
129 if (stat(script_path, &st) < 0)
130 die("Cannot stat %s: %m", script_path);
132 if (!S_ISREG(st.st_mode))
133 die("Not a regular file: %s", script_path);
134 if (!(st.st_mode & (S_ISUID | S_ISGID)))
135 die("Missing suid/sgid: %s", script_path);
137 use_uid = (st.st_mode & S_ISUID) ? st.st_uid : getuid();
138 use_gid = (st.st_mode & S_ISGID) ? st.st_gid : getgid();
139 DBG("Will use uid=%d gid=%d\n", (int) use_uid, (int) use_gid);
142 static void switch_ugid(void)
144 if (setresgid(getgid(), use_gid, use_gid) < 0)
145 die("Failed to set group id: %m");
147 if (setresuid(getuid(), use_uid, use_uid) < 0)
148 die("Failed to set user id: %m");
151 int main(int argc UNUSED, char **argv)
156 die("Must be run setuid");
158 struct passwd *pwd = getpwuid(getuid());
160 die("You don't exist");
162 openlog("suidgw", LOG_NDELAY | LOG_PID, LOG_AUTH);
164 if (!get_program_name(argv[0]))
165 die("Unable to parse program name %s", argv[0]);
171 syslog(LOG_INFO, "User %s executes %s with uid=%d, gid=%d",
172 pwd->pw_name, script_path, (int) use_uid, (int) use_gid);
174 if (execve(script_path, argv, sanitized_env) < 0)
175 die("Cannot execute %s: %m", script_path);
177 die("This must never happen");