talloc: added talloc_stackframe_exists()

This can be used to tell if a talloc stackframe is currently
available. Callers can use this to decide if they will use
talloc_tos() or instead use an alternative strategy. This gives us a
way to safely have calls to talloc_tos() in common code that may end
up in external libraries, as long as all talloc_tos() calls in these
pieces of common code check first that a stackframe is available.

2 files changed, 25 insertions, 0 deletions

diff --git a/lib/util/talloc_stack.c b/lib/util/talloc_stack.c
index 8e559cc20f..16e9d745d3 100644
--- a/lib/util/talloc_stack.c
+++ b/lib/util/talloc_stack.c
@@ -188,3 +188,20 @@ TALLOC_CTX *talloc_tos(void)
 
 	return ts->talloc_stack[ts->talloc_stacksize-1];
 }
+
+/*
+ * return true if a talloc stackframe exists
+ * this can be used to prevent memory leaks for code that can
+ * optionally use a talloc stackframe (eg. nt_errstr())
+ */
+
+bool talloc_stackframe_exists(void)
+{
+	struct talloc_stackframe *ts =
+		(struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
+
+	if (ts == NULL || ts->talloc_stacksize == 0) {
+		return false;
+	}
+	return true;
+}
diff --git a/lib/util/talloc_stack.h b/lib/util/talloc_stack.h
index 0e8fab3759..ec0c1c6f37 100644
--- a/lib/util/talloc_stack.h
+++ b/lib/util/talloc_stack.h
@@ -53,4 +53,12 @@ TALLOC_CTX *talloc_stackframe_pool(size_t poolsize);
 
 TALLOC_CTX *talloc_tos(void);
 
+/*
+ * return true if a talloc stackframe exists
+ * this can be used to prevent memory leaks for code that can
+ * optionally use a talloc stackframe (eg. nt_errstr())
+ */
+
+bool talloc_stackframe_exists(void);
+
 #endif