elf: Fix LD_AUDIT for modules with invalid version (BZ#24122)

elf: Fix LD_AUDIT for modules with invalid version (BZ#24122)

The error handling patch for invalid audit modules version access
invalid memory:

elf/rtld.c:

1454               unsigned int (*laversion) (unsigned int);
1455               unsigned int lav;
1456               if  (err_str == NULL
1457                    && (laversion = largs.result) != NULL
1458                    && (lav = laversion (LAV_CURRENT)) > 0
1459                    && lav <= LAV_CURRENT)
1460                 {
[...]
1526               else
1527                 {
1528                   /* We cannot use the DSO, it does not have the
1529                      appropriate interfaces or it expects something
1530                      more recent.  */
1531 #ifndef NDEBUG
1532                   Lmid_t ns = dlmargs.map->l_ns;
1533 #endif
1534                   _dl_close (dlmargs.map);
1535
1536                   /* Make sure the namespace has been cleared entirely.  */
1537                   assert (GL(dl_ns)[ns]._ns_loaded == NULL);
1538                   assert (GL(dl_ns)[ns]._ns_nloaded == 0);
1539
1540                   GL(dl_tls_max_dtv_idx) = tls_idx;
1541                   goto not_loaded;
1542                 }

1431           const char *err_str = NULL;
1432           bool malloced;
1433           (void) _dl_catch_error (&objname, &err_str, &malloced, dlmopen_doit,
1434                                   &dlmargs);
1435           if (__glibc_unlikely (err_str != NULL))
1436             {
1437             not_loaded:
1438               _dl_error_printf ("\
1439 ERROR: ld.so: object '%s' cannot be loaded as audit interface: %s; ignored.\n",
1440                                 name, err_str);
1441               if (malloced)
1442                 free ((char *) err_str);
1443             }

On failure the err_str will be NULL and _dl_debug_vdprintf does not handle
it properly:

elf/dl-misc.c:
200             case 's':
201               /* Get the string argument.  */
202               iov[niov].iov_base = va_arg (arg, char *);
203               iov[niov].iov_len = strlen (iov[niov].iov_base);
204               if (prec != -1)
205                 iov[niov].iov_len = MIN ((size_t) prec, iov[niov].iov_len);
206               ++niov;
207               break;

This patch fixes the issues and improves the error message.

Checked on x86_64-linux-gnu and i686-linux-gnu

	[BZ #24122]
	* elf/Makefile (tests): Add tst-audit13.
	(modules-names): Add tst-audit13mod1.
	(tst-audit13.out, LDFLAGS-tst-audit13mod1.so, tst-audit13-ENV): New
	rule.
	* elf/rtld.c (dl_main): Handle invalid audit module version.
	* elf/tst-audit13.c: New file.
	* elf/tst-audit13mod1.c: Likewise.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>