Adding Add/Remove Padding for PKCS7

inc/symcrypt.h

@@ -3078,10 +3078,14 @@ SymCryptPaddingPkcs7Remove(
 // Even if an error is returned, the pbDst buffer may or may not contain data from the message.
 // Callers should wipe the buffer even if an error is returned.
 // 
+// In case that the padding is invalid and the output buffer is too small, both the 
+// errors above are detected, but SYMCRYPT_INVALID_ARGUMENT gets precedence over 
+// SYMCRYPT_BUFFER_TOO_SMALL and the returned value will be SYMCRYPT_INVALID_ARGUMENT.
+// 
 // Note: Removal of PKCS7 padding is extremely sensitive to side channels.
 // For example, if a message is encrypted with AES-CBC and the attacker can modify 
 // the ciphertext and then determine whether a padding error occurrs during decryption,
-// then the attacker can use the presence or absense of the error to decrypt the message itself.
+// then the attacker can use the presence or absence of the error to decrypt the message itself.
 // This function takes great care not to reveal whether an error occurred, and hides
 // the size of the unpadded message. This is even true when writing to pbDst. If cbDst is large
 // enough, the code will write cbSrc-1 bytes to pbDst, using masking to only update the bytes of the

lib/paddingPkcs7.c

@@ -45,7 +45,7 @@ SymCryptPaddingPkcs7Add(
     //  perform the padding
     //
 
-    // cbSrc must be greater than zero. memcpy(,,0) is not defined!
+    // cbSrc must be greater than zero. memcpy(pbDst, NULL, 0) is not defined!
     if (pbDst != pbSrc && cbSrc > 0)
     {
         memcpy(pbDst, pbSrc, cbSrc);
@@ -154,6 +154,7 @@ cleanup:
     *pcbResult = cbResult;
 
     // Update scError with the two error masks.
+    // SYMCRYPT_INVALID_ARGUMENT gets precedence over SYMCRYPT_BUFFER_TOO_SMALL
     scError ^= mBufferSizeError & (scError ^ SYMCRYPT_BUFFER_TOO_SMALL);
     scError ^= mPaddingError & (scError ^ SYMCRYPT_INVALID_ARGUMENT);
 

unittest/lib/testScsTools.cpp

@@ -145,12 +145,10 @@ testScsMapUint32()
     GENRANDOM(&u32To2, sizeof(u32To2));
     GENRANDOM(&u32To3, sizeof(u32To3));
 
-
-    SYMCRYPT_UINT32_MAP map1 = { u32From1, u32To1 };
-    SYMCRYPT_UINT32_MAP map2 = { u32From2, u32To2 };
-    SYMCRYPT_UINT32_MAP map3 = { u32From2, u32To3 }; // multiple map entries may have the same 'from'
-
-    SYMCRYPT_UINT32_MAP pMap[2] = { map1, map2 };
+    SYMCRYPT_UINT32_MAP pMap[3] = { 
+        { u32From1, u32To1 }, 
+        { u32From2, u32To2 }, 
+        { u32From2, u32To3 } };     // multiple map entries may have the same 'from'
 
     //
     // Case 1: u32Input matches the 'from' field of only one entry