passing same buffer as input and output to mbedtls_cipher_update leads to error

[cdriper]

I ported your code to Visual Studio and found a critical bug in aes_decrypt() code (AES decryption worked in a wrong way).
It's forbidden to pass same buffers as input and output to mbedtls_cipher_update.

Quote from mbedtls_cipher_update description:

param output: buffer for the output data. Should be able to hold at least ilen + block_size. Cannot be the same buffer as input!

Possible fix (with extra buffer allocation):

void aes_decrypt(aes_ctx_t *ctx, void *dst, const void *src, size_t l) 
{
    int bExtraBuff = 0; 

    if (src == dst)
    {
        bExtraBuff = 1;

        dst = malloc(l);
        assert(dst);
    }

    size_t out_len = 0;
    
    /* Prepare context */
    mbedtls_cipher_reset(&ctx->cipher_dec);
    
    /* XTS doesn't need per-block updating */
    if (mbedtls_cipher_get_cipher_mode(&ctx->cipher_dec) == MBEDTLS_MODE_XTS)
        mbedtls_cipher_update(&ctx->cipher_dec, (const unsigned char * )src, l, (unsigned char *)dst, &out_len);
    else
    {
        unsigned int blk_size = mbedtls_cipher_get_block_size(&ctx->cipher_dec);
        
        /* Do per-block updating */
        for (int offset = 0; (unsigned int)offset < l; offset += blk_size)
        {
            int len = ((unsigned int)(l - offset) > blk_size) ? blk_size : (unsigned int) (l - offset);
            mbedtls_cipher_update(&ctx->cipher_dec, (const unsigned char * )src + offset, len, (unsigned char *)dst + offset, &out_len);
        }
    }
    
    /* Flush all data */
    mbedtls_cipher_finish(&ctx->cipher_dec, NULL, NULL);

    if (bExtraBuff)
    {
        memcpy( (void*)src, dst, l );
        free(dst);
    }
}