Check for overflow on input lengths

[sneves]

On 64-bit architectures it is currently possible to have passwords that hash and verify to the same value, as demonstrated below:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include "argon2.h"

int main(void) {
    unsigned char out[32];
    char encoded[108];
    int ret;

    const char pwd[] = "a not very long password";
    const char salt[] = "a very long salt";

    ret = argon2_hash(2, 1 << 16, 1, pwd, strlen(pwd), salt, strlen(salt), out,
                      sizeof(out), encoded, sizeof(encoded), Argon2_i, ARGON2_VERSION_13);
    assert(ret == ARGON2_OK);

    ret = argon2_verify(encoded, pwd, strlen(pwd), Argon2_i);
    assert(ret == ARGON2_OK);

    char * pwd2 = (char *)calloc(strlen(pwd) + (1ULL << 32) + 1, 1);
    memset(pwd2, 'A', strlen(pwd) + (1ULL << 32));
    memcpy(pwd2, pwd, strlen(pwd));

    ret = argon2_verify(encoded, pwd2, strlen(pwd2), Argon2_i);
    assert(ret == ARGON2_OK);

    printf("BUG\n");
}

The reason for this is that argon2_verify receives a size_t password length, but it is converted to uint32_t before being verified in validate_inputs. Therefore truncation can occur.

Checks to prevent this used to exist on argon2_hash but were removed in #131. On argon2_verify, as far as I can tell, they never existed.

[codecov-io]

Codecov Report

Merging #195 into master will decrease coverage by -0.41%.
The diff coverage is 42.85%.

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
- Coverage   68.38%   67.98%   -0.41%     
==========================================
  Files           9        9              
  Lines        1006     1012       +6     
  Branches      163      166       +3     
==========================================
  Hits          688      688              
- Misses        242      245       +3     
- Partials       76       79       +3

Impacted Files	Coverage Δ
src/argon2.c	43.04% <42.85%> (-1.16%)	❌
src/opt.c	92.59% <0%> (ø)	✅

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 69341f7...9f1e531. Read the comment docs.