pam_timestamp: fix potential directory traversal issue (ticket #27)

pam_timestamp uses values of PAM_RUSER and PAM_TTY as components of
the timestamp pathname it creates, so extra care should be taken to
avoid potential directory traversal issues.

* modules/pam_timestamp/pam_timestamp.c (check_tty): Treat
"." and ".." tty values as invalid.
(get_ruser): Treat "." and ".." ruser values, as well as any ruser
value containing '/', as invalid.

Fixes CVE-2014-2583.

Reported-by: Sebastian Krahmer <krahmer@suse.de>

diff --git a/modules/pam_timestamp/pam_timestamp.c b/modules/pam_timestamp/pam_timestamp.c
index 51937333ec5cf2eb9963d4469b36568764f58d29..b3f08b1ff388f47c9b89fb0f6876e37b7cd242f6 100644 (file)
--- a/modules/pam_timestamp/pam_timestamp.c
+++ b/modules/pam_timestamp/pam_timestamp.c
@@ -158,7 +158,7 @@ check_tty(const char *tty)
                tty = strrchr(tty, '/') + 1;
        }
        /* Make sure the tty wasn't actually a directory (no basename). */
-       if (strlen(tty) == 0) {
+       if (!strlen(tty) || !strcmp(tty, ".") || !strcmp(tty, "..")) {
                return NULL;
        }
        return tty;
@@ -243,6 +243,17 @@ get_ruser(pam_handle_t *pamh, char *ruserbuf, size_t ruserbuflen)
                if (pwd != NULL) {
                        ruser = pwd->pw_name;
                }
+       } else {
+               /*
+                * This ruser is used by format_timestamp_name as a component
+                * of constructed timestamp pathname, so ".", "..", and '/'
+                * are disallowed to avoid potential path traversal issues.
+                */
+               if (!strcmp(ruser, ".") ||
+                   !strcmp(ruser, "..") ||
+                   strchr(ruser, '/')) {
+                       ruser = NULL;
+               }
        }
        if (ruser == NULL || strlen(ruser) >= ruserbuflen) {
                *ruserbuf = '\0';