Fix for segfault in __ast_rwlock_destroy with DEBUG_THREADS

If DEBUG_THREADS is enabled __ast_rwlock_destroy causes a segfault while trying
to access a possible NULL t->track object.  A NULL check has been added before
trying to access the memory.

(closes issue ASTERISK-21724)
Reported by: Corey Farrell
Fixed by: Corey Farrell
Patches:
	ast_rwlock_destroy-segv.patch uploaded by Corey Farrell (license 5909)
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Merged revisions 388838 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 388839 from http://svn.asterisk.org/svn/asterisk/branches/11

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@388840 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/main/lock.c b/main/lock.c
index 3c9fbd4dbd5454304508f96e032475e422a7d54f..902d631193c2a3910dfc18530ad6afc5e20b27ce 100644 (file)
--- a/main/lock.c
+++ b/main/lock.c
@@ -745,7 +745,7 @@ int __ast_rwlock_destroy(const char *filename, int lineno, const char *func, con
                __ast_mutex_logger("%s line %d (%s): Error destroying rwlock %s: %s\n",
                                filename, lineno, func, rwlock_name, strerror(res));
        }
-       if (t->tracking) {
+       if (t->tracking && lt) {
                ast_reentrancy_lock(lt);
                lt->file[0] = filename;
                lt->lineno[0] = lineno;