pam_lastlog: prevent crash due to reduced 'fsize' limit

[linux-pam] / modules / pam_lastlog / pam_lastlog.c

diff --git a/modules/pam_lastlog/pam_lastlog.c b/modules/pam_lastlog/pam_lastlog.c
index e980c0478a8ec97bf01f1d68653559870469f29c..a135c9f7e7ec86a07875b5d600023e90b53223d7 100644 (file)
--- a/modules/pam_lastlog/pam_lastlog.c
+++ b/modules/pam_lastlog/pam_lastlog.c
@@ -25,6 +25,8 @@
 #include <stdio.h>
 #include <string.h>
 #include <sys/types.h>
+#include <sys/time.h>
+#include <sys/resource.h>
 #include <syslog.h>
 #include <unistd.h>
 
@@ -82,15 +84,16 @@ struct lastlog {
 
 /* argument parsing */
 
-#define LASTLOG_DATE        01  /* display the date of the last login */
-#define LASTLOG_HOST        02  /* display the last host used (if set) */
-#define LASTLOG_LINE        04  /* display the last terminal used */
-#define LASTLOG_NEVER      010  /* display a welcome message for first login */
-#define LASTLOG_DEBUG      020  /* send info to syslog(3) */
-#define LASTLOG_QUIET      040  /* keep quiet about things */
-#define LASTLOG_WTMP      0100  /* log to wtmp as well as lastlog */
-#define LASTLOG_BTMP      0200  /* display failed login info from btmp */
-#define LASTLOG_UPDATE    0400  /* update the lastlog and wtmp files (default) */
+#define LASTLOG_DATE          01  /* display the date of the last login */
+#define LASTLOG_HOST          02  /* display the last host used (if set) */
+#define LASTLOG_LINE          04  /* display the last terminal used */
+#define LASTLOG_NEVER        010  /* display a welcome message for first login */
+#define LASTLOG_DEBUG        020  /* send info to syslog(3) */
+#define LASTLOG_QUIET        040  /* keep quiet about things */
+#define LASTLOG_WTMP        0100  /* log to wtmp as well as lastlog */
+#define LASTLOG_BTMP        0200  /* display failed login info from btmp */
+#define LASTLOG_UPDATE      0400  /* update the lastlog and wtmp files (default) */
+#define LASTLOG_UNLIMITED  01000  /* unlimited file size (ignore 'fsize' limit) */
 
 static int
 _pam_auth_parse(pam_handle_t *pamh, int flags, int argc, const char **argv,
@@ -158,6 +161,8 @@ _pam_session_parse(pam_handle_t *pamh, int flags, int argc, const char **argv)
            ctrl &= ~(LASTLOG_WTMP|LASTLOG_UPDATE);
        } else if (!strcmp(*argv,"showfailed")) {
            ctrl |= LASTLOG_BTMP;
+       } else if (!strcmp(*argv,"unlimited")) {
+           ctrl |= LASTLOG_UNLIMITED;
        } else {
            pam_syslog(pamh, LOG_ERR, "unknown option: %s", *argv);
        }
@@ -373,6 +378,12 @@ static int
 last_login_write(pam_handle_t *pamh, int announce, int last_fd,
                 uid_t uid, const char *user)
 {
+    static struct rlimit no_limit = {
+       RLIM_INFINITY,
+       RLIM_INFINITY
+    };
+    struct rlimit old_limit;
+    int setrlimit_res;
     struct flock last_lock;
     struct lastlog last_login;
     time_t ll_time;
@@ -427,6 +438,31 @@ last_login_write(pam_handle_t *pamh, int announce, int last_fd,
         sleep(LASTLOG_IGNORE_LOCK_TIME);
     }
 
+    /*
+     * Failing to set the 'fsize' limit is not a fatal error. We try to write
+     * lastlog anyway, under the risk of dying due to a SIGXFSZ.
+     */
+    D(("setting limit for 'fsize'"));
+
+    if ((announce & LASTLOG_UNLIMITED) == 0) {    /* don't set to unlimted */
+       setrlimit_res = -1;
+    } else if (getrlimit(RLIMIT_FSIZE, &old_limit) == 0) {
+       if (old_limit.rlim_cur == RLIM_INFINITY) {    /* already unlimited */
+           setrlimit_res = -1;
+       } else {
+           setrlimit_res = setrlimit(RLIMIT_FSIZE, &no_limit);
+           if (setrlimit_res != 0)
+               pam_syslog(pamh, LOG_WARNING, "Could not set limit for 'fsize': %m");
+       }
+    } else {
+       setrlimit_res = -1;
+       if (errno == EINVAL) {
+           pam_syslog(pamh, LOG_INFO, "Limit for 'fsize' not supported: %m");
+       } else {
+           pam_syslog(pamh, LOG_WARNING, "Could not get limit for 'fsize': %m");
+       }
+    }
+
     D(("writing to the lastlog file"));
     if (pam_modutil_write (last_fd, (char *) &last_login,
                           sizeof (last_login)) != sizeof(last_login)) {
@@ -434,6 +470,18 @@ last_login_write(pam_handle_t *pamh, int announce, int last_fd,
        retval = PAM_SERVICE_ERR;
     }
 
+    /*
+     * Failing to restore the 'fsize' limit is a fatal error.
+     */
+    D(("restoring limit for 'fsize'"));
+    if (setrlimit_res == 0) {
+       setrlimit_res = setrlimit(RLIMIT_FSIZE, &old_limit);
+       if (setrlimit_res != 0) {
+           pam_syslog(pamh, LOG_ERR, "Could not restore limit for 'fsize': %m");
+           retval = PAM_SERVICE_ERR;
+       }
+    }
+
     last_lock.l_type = F_UNLCK;
     (void) fcntl(last_fd, F_SETLK, &last_lock);        /* unlock */
     D(("unlocked"));