Make zap() more reliable

The gcc assembly version of zap() could still be optimized out under
gcc 5.1 or later, and the krb5int_zap() function could be optimized
out with link-time optimization.  Based on work by Zhaomo Yang and
Brian Johannesmeyer, use the C11 memset_s() when available, then fall
back to a memory barrier with gcc or clang, and finally fall back to
using krb5int_zap().  Modify krb5int_zap() to use a volatile pointer
in case link-time optimization is used.

ticket: 8514 (new)
target_version: 1.15-next
target_version: 1.14-next
tags: pullup

1 files changed, 4 insertions, 1 deletions

diff --git a/src/util/support/zap.c b/src/util/support/zap.c
index 48512a9..ed31630 100644
--- a/src/util/support/zap.c
+++ b/src/util/support/zap.c
@@ -34,5 +34,8 @@
 
 void krb5int_zap(void *ptr, size_t len)
 {
-    memset(ptr, 0, len);
+    volatile char *p = ptr;
+
+    while (len--)
+        *p++ = '\0';
 }