Tidy ChaCha20 counter limit handling

Signed-off-by: Ben Taylor <[email protected]>

include/mbedtls/chacha20.h

@@ -38,7 +38,8 @@ extern "C" {
 typedef struct mbedtls_chacha20_context {
     uint32_t MBEDTLS_PRIVATE(state)[16];          /*! The state (before round operations). */
     uint8_t  MBEDTLS_PRIVATE(keystream8)[64];     /*! Leftover keystream bytes. */
-    size_t MBEDTLS_PRIVATE(keystream_bytes_used); /*! Number of keystream bytes already used. */
+    size_t MBEDTLS_PRIVATE(keystream_bytes_used); /*! Number of keystream bytes already used,
+                                                   * or an internal sentinel value. */
 }
 mbedtls_chacha20_context;
 

library/chacha20.c

@@ -31,7 +31,7 @@
 
 #define CHACHA20_BLOCK_SIZE_BYTES (4U * 16U)
 
-#define CHACHA20_MAX_BLOCKS 0xFFFFFFFF
+#define CHACHA20_MAX_BLOCKS UINT32_MAX
 
 #define CHACHA20_COUNTER_EXHAUSTED (CHACHA20_BLOCK_SIZE_BYTES + 1U)
 

tests/suites/test_suite_chacha20.function

@@ -96,6 +96,7 @@ void chacha20_input_len_too_long(void)
 
     /* Consume the rest of the final counter block, then reject more input. */
     TEST_EQUAL(mbedtls_chacha20_update(&ctx, 63, input, output), 0);
+    TEST_EQUAL(mbedtls_chacha20_update(&ctx, 0, NULL, NULL), 0);
     TEST_EQUAL(mbedtls_chacha20_update(&ctx, 1, input, output),
                MBEDTLS_ERR_CHACHA20_BAD_INPUT_DATA);