Re: [PATCH 1/4] evm: check hash algorithm passed to init_desc()

From: Mimi Zohar <zohar@linux.ibm.com>
To: Roberto Sassu <roberto.sassu@huawei.com>,
	dmitry.kasatkin@huawei.com, mjg59@google.com
Cc: linux-integrity@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org, silviu.vlasceanu@huawei.com,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/4] evm: check hash algorithm passed to init_desc()
Date: Mon, 20 May 2019 17:19:03 -0400	[thread overview]
Message-ID: <1558387143.4039.74.camel@linux.ibm.com> (raw)
In-Reply-To: <20190516161257.6640-1-roberto.sassu@huawei.com>

On Thu, 2019-05-16 at 18:12 +0200, Roberto Sassu wrote:
> This patch prevents memory access beyond the evm_tfm array by checking the
> validity of the index (hash algorithm) passed to init_desc(). The hash
> algorithm can be arbitrarily set if the security.ima xattr type is not
> EVM_XATTR_HMAC.
> 
> Fixes: 5feeb61183dde ("evm: Allow non-SHA1 digital signatures")
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> Cc: stable@vger.kernel.org

Thanks!

> ---
>  security/integrity/evm/evm_crypto.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> index e11564eb645b..82a38e801ee4 100644
> --- a/security/integrity/evm/evm_crypto.c
> +++ b/security/integrity/evm/evm_crypto.c
> @@ -89,6 +89,9 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
>  		tfm = &hmac_tfm;
>  		algo = evm_hmac;
>  	} else {
> +		if (hash_algo >= HASH_ALGO__LAST)
> +			return ERR_PTR(-EINVAL);
> +
>  		tfm = &evm_tfm[hash_algo];
>  		algo = hash_algo_name[hash_algo];
>  	}