From d6390b368579fa9f5e546e6a25c19ab1734412a7 Mon Sep 17 00:00:00 2001
From: Kaspar Schleiser <kaspar@schleiser.de>
Date: Thu, 17 Jan 2019 10:56:34 +0100
Subject: [PATCH] hashes/sha256: don't call memcpy if len==0

---
 sys/hashes/sha256.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sys/hashes/sha256.c b/sys/hashes/sha256.c
index 32b1845f12..6b843e09ea 100644
--- a/sys/hashes/sha256.c
+++ b/sys/hashes/sha256.c
@@ -223,7 +223,9 @@ void sha256_update(sha256_context_t *ctx, const void *data, size_t len)
 
     /* Handle the case where we don't need to perform any transforms */
     if (len < 64 - r) {
-        memcpy(&ctx->buf[r], data, len);
+        if (len > 0) {
+            memcpy(&ctx->buf[r], data, len);
+        }
         return;
     }