libbb: add bb_unsetenv (taken from hush).

udhcpc: stop filtering environment passed to the script.
crond: fix uncovered potential bug (failing unsetenv)
mdev: fix uncovered potential bug (failing unsetenv)
tcp, udpsvd: fix uncovered potential bug (failing unsetenv)

function                                             old     new   delta
safe_setenv                                            -      58     +58
bb_unsetenv                                            -      55     +55
builtin_unset                                        139     138      -1
tcpudpsvd_main                                      1843    1830     -13
free_strings_and_unsetenv                             87      53     -34
udhcp_run_script                                    1186    1133     -53
safe_setenv4                                          62       -     -62
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 0/4 up/down: 113/-163)          Total: -50 bytes

1 files changed, 5 insertions, 7 deletions

diff --git a/miscutils/crond.c b/miscutils/crond.c
index 732fbb147..12560fa36 100644
--- a/miscutils/crond.c
+++ b/miscutils/crond.c
@@ -252,14 +252,12 @@ int crond_main(int argc UNUSED_PARAM, char **argv)
 /* We set environment *before* vfork (because we want to use vfork),
  * so we cannot use setenv() - repeated calls to setenv() may leak memory!
  * Using putenv(), and freeing memory after unsetenv() won't leak */
-static void safe_setenv4(char **pvar_val, const char *var, const char *val /*, int len*/)
+static void safe_setenv(char **pvar_val, const char *var, const char *val)
 {
-        const int len = 4; /* both var names are 4 char long */
         char *var_val = *pvar_val;
 
         if (var_val) {
-                var_val[len] = '\0'; /* nuke '=' */
-                unsetenv(var_val);
+                bb_unsetenv(var_val);
                 free(var_val);
         }
         *pvar_val = xasprintf("%s=%s", var, val);
@@ -270,10 +268,10 @@ static void safe_setenv4(char **pvar_val, const char *var, const char *val /*, i
 static void SetEnv(struct passwd *pas)
 {
 #if SETENV_LEAKS
-        safe_setenv4(&env_var_user, "USER", pas->pw_name);
-        safe_setenv4(&env_var_home, "HOME", pas->pw_dir);
+        safe_setenv(&env_var_user, "USER", pas->pw_name);
+        safe_setenv(&env_var_home, "HOME", pas->pw_dir);
         /* if we want to set user's shell instead: */
-        /*safe_setenv(env_var_user, "SHELL", pas->pw_shell, 5);*/
+        /*safe_setenv(env_var_user, "SHELL", pas->pw_shell);*/
 #else
         xsetenv("USER", pas->pw_name);
         xsetenv("HOME", pas->pw_dir);