modules: make use of secure memory erasure

Use empty initialization of structs to minimize the memset() usage, to
reduce the amount of calls which are not sensitive.

Non trivial changes:

- pam_env:
  * erase environment variables where possible

- pam_exec:
  * erase responce on error
  * erase auth token

- pam_pwhistory:
  * erase buffers containing old passwords

- pam_selinux: skip overwriting data structure consisting of only
  pointers to insensitive data, which also gets free'd afterwards (so
  it currently does not protect against double-free or use-after-free on
  the member pointers)

- pam_unix: erase cipher data in more places

- pam_userdb: erase password hashes

1 files changed, 5 insertions, 5 deletions

diff --git a/modules/pam_lastlog/pam_lastlog.c b/modules/pam_lastlog/pam_lastlog.c
index 797a61ce..ec515f56 100644
--- a/modules/pam_lastlog/pam_lastlog.c
+++ b/modules/pam_lastlog/pam_lastlog.c
@@ -366,11 +366,11 @@ last_login_read(pam_handle_t *pamh, int announce, int last_fd, uid_t uid, time_t
 
     /* cleanup */
  cleanup:
-    memset(&last_login, 0, sizeof(last_login));
-    _pam_overwrite(date);
-    _pam_overwrite(host);
+    pam_overwrite_object(&last_login);
+    pam_overwrite_string(date);
+    pam_overwrite_string(host);
     _pam_drop(host);
-    _pam_overwrite(line);
+    pam_overwrite_string(line);
     _pam_drop(line);
 
     return retval;
@@ -502,7 +502,7 @@ last_login_write(pam_handle_t *pamh, int announce, int last_fd,
     }
 
     /* cleanup */
-    memset(&last_login, 0, sizeof(last_login));
+    pam_overwrite_object(&last_login);
 
     return retval;
 }