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From: "Juan Manuel Guerrero" <st001906 AT hrz1 DOT hrz DOT tu-darmstadt DOT de>
Organization: Darmstadt University of Technology
To: djgpp-workers AT delorie DOT com
Date: Thu, 25 Nov 2004 11:02:30 +0200
MIME-Version: 1.0
Subject: A fix for popen().
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Reply-To: djgpp-workers AT delorie DOT com

Please look at the following code snippet from popen.c:

    /* redirect stdout */
    if (!(l1->fp = freopen(temp_name, "wb", stdout)))
      goto error;

    /* make sure file is removed on abnormal exit */
    l1->fp->_flag |= _IORMONCL;
    l1->fp->_name_to_remove = temp_name;

    /* execute command */
    l1->exit_status = system(cm);

    /* don't remove file while closing */
    l1->fp->_flag &= ~_IORMONCL;
    l1->fp->_name_to_remove = NULL;

    /* close file */
    fclose(l1->fp);

    /* reopen real stdout */
    if (dup2(fd, fileno(stdout)) == -1)
      goto error;


As can be seen l1->fp contains the file pointer of stdout that has been redirected to
the temp file. After the system() call, the file pointer is passed to fclose().
When fclose() returns the file descriptor of stdout's file pointer has been set to -1.
Now, the call of fileno() with stdout's file pointer closed will return exactly this file
descriptor of -1. If dup2() is called with a file descriptor of -1,  the call always
will fail making popen() always fail for pipe reading mode too.
The failure of popen() is one reason why the eval test of the testsuite of sed 4.1.2 fails
if the package has been compiled with djdev204 and partially works if compiled with djdev203.
djdev203 does not contain this bug. Unfortunatly now that this bug has been fixed a new one
appers. Now the e command dies with a SIGSEGV in free() of djdev204. This must still be
investigated.

This can be solved with the small patch below. dup2() closes the new file descriptor anyway
so there is no reason to call fclose() at all. Please note that I have no write access, so someone
else must take care about this issue.

I assume that djdev204 will not be released quite soon, so the best way to fix sed 4.1.2
is to disable the evaluate command at all.


Regards,
Juan M. Guerrero



diff -aruU4 djgpp.orig/src/libc/posix/stdio/popen.c djgpp/src/libc/posix/stdio/popen.c
--- djgpp.orig/src/libc/posix/stdio/popen.c	2004-06-02 04:08:32.000000000 +0000
+++ djgpp/src/libc/posix/stdio/popen.c	2004-11-25 02:56:38.000000000 +0000
@@ -122,11 +122,8 @@
     /* reopen real stdout */
     if (dup2(fd, fileno(stdout)) == -1)
       goto error;
 
-    /* close duplicate stdout */
-    close(fd);
-
     /* if cmd couldn't be run, make sure we return NULL */
     if (l1->exit_status == -1)
       goto error;
   }