From 56fc5bbf879dc21e60c3366ea69268e46005b60f Mon Sep 17 00:00:00 2001
From: Juliusz Sosinowicz <juliusz@wolfssl.com>
Date: Fri, 21 Jul 2023 14:48:28 +0200
Subject: [PATCH] Dtls13GetRnMask: Correctly get chacha counter on BE systems

The issue was that BIG_ENDIAN is defined in endian.h (on linux). Our define is BIG_ENDIAN_ORDER.
---
 src/dtls13.c             |  8 +-------
 wolfcrypt/src/misc.c     |  9 +++++++++
 wolfssl/wolfcrypt/misc.h | 13 +++++++------
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/src/dtls13.c b/src/dtls13.c
index b5fecafd7..e8a2947d8 100644
--- a/src/dtls13.c
+++ b/src/dtls13.c
@@ -274,13 +274,7 @@ static int Dtls13GetRnMask(WOLFSSL* ssl, const byte* ciphertext, byte* mask,
         if (c->chacha == NULL)
             return BAD_STATE_E;
 
-        /* assuming CIPHER[0..3] should be interpreted as little endian 32-bits
-           integer. The draft rfc isn't really clear on that. See sec 4.2.3 of
-           the draft. See also Section 2.3 of the Chacha RFC. */
-        XMEMCPY(&counter, ciphertext, sizeof(counter));
-#ifdef BIG_ENDIAN
-        counter = ByteReverseWord32(counter);
-#endif /* BIG_ENDIAN */
+        ato32le(ciphertext, &counter);
 
         ret = wc_Chacha_SetIV(c->chacha, &ciphertext[4], counter);
         if (ret != 0)
diff --git a/wolfcrypt/src/misc.c b/wolfcrypt/src/misc.c
index 8ccf766ba..bc1ea8fa9 100644
--- a/wolfcrypt/src/misc.c
+++ b/wolfcrypt/src/misc.c
@@ -472,6 +472,15 @@ WC_MISC_STATIC WC_INLINE void ato32(const byte* c, word32* wc_u32)
                (word32)c[3];
 }
 
+/* convert opaque to 32 bit integer. Interpret as little endian. */
+WC_MISC_STATIC WC_INLINE void ato32le(const byte* c, word32* wc_u32)
+{
+    *wc_u32 =  (word32)c[0] |
+              ((word32)c[1] << 8) |
+              ((word32)c[2] << 16) |
+              ((word32)c[3] << 24);
+}
+
 
 WC_MISC_STATIC WC_INLINE word32 btoi(byte b)
 {
diff --git a/wolfssl/wolfcrypt/misc.h b/wolfssl/wolfcrypt/misc.h
index e433a1a3c..45dfb7621 100644
--- a/wolfssl/wolfcrypt/misc.h
+++ b/wolfssl/wolfcrypt/misc.h
@@ -102,12 +102,13 @@ void   ByteReverseWords64(word64* out, const word64* in, word32 byteCount);
 
 
 void c32to24(word32 in, word24 out);
-void c16toa(word16 u16, byte* c);
-void c32toa(word32 u32, byte* c);
-void c24to32(const word24 u24, word32* u32);
-void ato16(const byte* c, word16* u16);
-void ato24(const byte* c, word32* u24);
-void ato32(const byte* c, word32* u32);
+void c16toa(word16 wc_u16, byte* c);
+void c32toa(word32 wc_u32, byte* c);
+void c24to32(const word24 wc_u24, word32* wc_u32);
+void ato16(const byte* c, word16* wc_u16);
+void ato24(const byte* c, word32* wc_u24);
+void ato32(const byte* c, word32* wc_u32);
+void ato32le(const byte* c, word32* wc_u32);
 word32 btoi(byte b);
 
 WOLFSSL_LOCAL signed char HexCharToByte(char ch);