Add ERR_clear_last_mark()

This allows callers to set a mark, and then clear it without removing
the errors.  Useful in case an error is encountered that should be
returned up the call stack.

Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4094)

1 files changed, 23 insertions, 0 deletions

diff --git a/crypto/err/err.c b/crypto/err/err.c
index 9db3530330..07911e25b2 100644
--- a/crypto/err/err.c
+++ b/crypto/err/err.c
@@ -812,3 +812,26 @@ int ERR_pop_to_mark(void)
     es->err_flags[es->top] &= ~ERR_FLAG_MARK;
     return 1;
 }
+
+int ERR_clear_last_mark(void)
+{
+    ERR_STATE *es;
+    int top;
+
+    es = ERR_get_state();
+    if (es == NULL)
+        return 0;
+
+    top = es->top;
+    while (es->bottom != top
+           && (es->err_flags[top] & ERR_FLAG_MARK) == 0) {
+        top -= 1;
+        if (top == -1)
+            top = ERR_NUM_ERRORS - 1;
+    }
+
+    if (es->bottom == top)
+        return 0;
+    es->err_flags[top] &= ~ERR_FLAG_MARK;
+    return 1;
+}