Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
From:   Yiyuan guo <yguoaz@gmail.com>
Date:   Fri, 21 May 2021 11:23:36 +0800
Message-ID: <CAM7=BFrCTTuBkYb-ceX5C=e8VhAuWBVb_pYQ+K0LB1gn3h=hqA@mail.gmail.com>
Subject: A possible divide by zero bug in drbg_ctr_df
To:     herbert@gondor.apana.org.au
Cc:     linux-crypto@vger.kernel.org, davem@davemloft.net,
        Yiyuan guo <yguoaz@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

In crypto/drbg.c, the function drbg_ctr_df has the following code:

padlen = (inputlen + sizeof(L_N) + 1) % (drbg_blocklen(drbg));

However, the function drbg_blocklen may return zero:

static inline __u8 drbg_blocklen(struct drbg_state *drbg)
{
    if (drbg && drbg->core)
        return drbg->core->blocklen_bytes;
    return 0;
}

Is it possible to trigger a divide by zero problem here?