Re: [PATCH v12 1/9] stdlib: Add arc4random, arc4random_buf, and arc4random_uniform (BZ #4417)

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 22/07/22 09:35, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
>> diff --git a/stdlib/chacha20.c b/stdlib/chacha20.c
>> new file mode 100644
>> index 0000000000..77e37655cd
>> --- /dev/null
>> +++ b/stdlib/chacha20.c
>> @@ -0,0 +1,179 @@
> 
>> +static void
>> +chacha20_crypt (uint32_t *state, uint8_t *dst, const uint8_t *src)
>> +{
>> +  size_t bytes = CHACHA20_BUFSIZE;
>> +  while (bytes >= CHACHA20_BLOCK_SIZE)
> 
> That doesn't look right.  No bytes variable.
> 
> The chacha20_crypt functions should probably use arguments in the style
> of
> 
>   uint8_t dst[static CHACHA20_BUFSIZE]
> 
> for compiler size checking.

Would it be acceptable?

diff --git a/stdlib/chacha20.c b/stdlib/chacha20.c
index 07b7b203f2..4217ecb06f 100644
--- a/stdlib/chacha20.c
+++ b/stdlib/chacha20.c
@@ -166,14 +166,15 @@ chacha20_block (uint32_t *state, uint8_t *dst, const uint8_t *src)

 static void
 __attribute_maybe_unused__
-chacha20_crypt_generic (uint32_t *state, uint8_t *dst, const uint8_t *src)
+chacha20_crypt_generic (uint32_t *state, uint8_t dst[static CHACHA20_BUFSIZE],
+                       const uint8_t *src)
 {
-  size_t bytes = CHACHA20_BUFSIZE;
-  while (bytes >= CHACHA20_BLOCK_SIZE)
+  size_t dstlen = CHACHA20_BUFSIZE;
+  while (dstlen >= CHACHA20_BLOCK_SIZE)
     {
       chacha20_block (state, dst, src);

-      bytes -= CHACHA20_BLOCK_SIZE;
+      dstlen -= CHACHA20_BLOCK_SIZE;
       dst += CHACHA20_BLOCK_SIZE;
       src += CHACHA20_BLOCK_SIZE;
     }