Commit 6657f12f authored by Thomas Lopatic's avatar Thomas Lopatic Committed by Daniel Stenberg
Browse files

fix the alarm()-based DNS timeout 

Looking at the code of Curl_resolv_timeout() in hostip.c, I think
that in case of a timeout, the signal handler for SIGALRM never
gets removed. I think that in my case it gets executed at some
point later on when execution has long left Curl_resolv_timeout()
or even the cURL library.

The code that is jumped to with siglongjmp() simply sets the
error message to "name lookup timed out" and then returns with
CURLRESOLV_ERROR. I guess that instead of simply returning
without cleaning up, the code should have a goto that jumps to
the spot right after the call to Curl_resolv().
parent 3cd5b1cf

lib/hostip.c

+15 −9
Original line number Diff line number Diff line
@@ -571,15 +571,6 @@ int Curl_resolv_timeout(struct connectdata *conn, 
    return CURLRESOLV_TIMEDOUT;



  if (timeout > 0) {

    /* This allows us to time-out from the name resolver, as the timeout

       will generate a signal and we will siglongjmp() from that here.

       This technique has problems (see alarmfunc). */

      if(sigsetjmp(curl_jmpenv, 1)) {

        /* this is coming from a siglongjmp() after an alarm signal */

        failf(data, "name lookup timed out");

        return CURLRESOLV_ERROR;

      }



    /*************************************************************

     * Set signal handler to catch SIGALRM

     * Store the old value to be able to set it back later!
@@ -605,6 +596,19 @@ int Curl_resolv_timeout(struct connectdata *conn, 
    /* alarm() makes a signal get sent when the timeout fires off, and that

       will abort system calls */

    prev_alarm = alarm((unsigned int) (timeout/1000L));



    /* This allows us to time-out from the name resolver, as the timeout

       will generate a signal and we will siglongjmp() from that here.

       This technique has problems (see alarmfunc).

       This should be the last thing we do before calling Curl_resolv(),

       as otherwise we'd have to worry about variables that get modified

       before we invoke Curl_resolv() (and thus use "volatile"). */

    if(sigsetjmp(curl_jmpenv, 1)) {

      /* this is coming from a siglongjmp() after an alarm signal */

      failf(data, "name lookup timed out");

      rc = CURLRESOLV_ERROR;

      goto clean_up;

    }

  }



#else
@@ -621,6 +625,8 @@ int Curl_resolv_timeout(struct connectdata *conn, 
   */

  rc = Curl_resolv(conn, hostname, port, entry);



clean_up:



#ifdef USE_ALARM_TIMEOUT

  if (timeout > 0) {