[PATCH] Fix threading support in talloc_stackframe

[Ralph Böhme]

Hi!

Just stumpled across this nice little crash in talloc_stackframe after enabling
thread-safety and using it in a vfs_xattr_tdb patch.

Please review carefully and push if happy. Thanks!

-slow

-- 
Ralph Boehme, Samba Team       https://samba.org/
Samba Developer, SerNet GmbH   https://sernet.de/en/samba/
GPG Key Fingerprint:           FAE2 C608 8A24 2520 51C5
                               59E4 AA1E 9B71 2639 9E46
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From 6d8c745a1bab7637e697f4d8d9b7f10f5750ca35 Mon Sep 17 00:00:00 2001
From: Ralph Boehme <slow at samba.org>
Date: Tue, 3 Jul 2018 15:30:33 +0200
Subject: [PATCH] lib: smb_threads: fix access before init bug

talloc_stackframe_internal() calls SMB_THREAD_GET_TLS(global_ts)  which
calls smb_get_tls_pthread() in the POSIX pthread wrapper implementation.

If SMB_THREAD_SET_TLS() hasn't been called before, global_ts is NULL and
smb_get_tls_pthread dereferences it so it crashes.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13505

Signed-off-by: Ralph Boehme <slow at samba.org>
---
 lib/util/smb_threads.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/util/smb_threads.h b/lib/util/smb_threads.h
index 9a096167743..67d05b8c411 100644
--- a/lib/util/smb_threads.h
+++ b/lib/util/smb_threads.h
@@ -119,6 +119,9 @@ static int smb_set_tls_pthread(void *pkey, const void *pval, const char *locatio
  \
 static void *smb_get_tls_pthread(void *pkey, const char *location) \
 { \
+	if (pkey == NULL) { \
+		return NULL; \
+	} \
         return pthread_getspecific(*(pthread_key_t *)pkey); \
 } \
  \
-- 
2.13.6