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Subject: Re: [PATCH] crypto: ablkcipher.c:  Cleaning up missing null-terminate in conjunction with strncpy
From: Mark D Rustad <mrustad@gmail.com>
In-Reply-To: <1406383757-1753-1-git-send-email-rickard_strandqvist@spectrumdigital.se>
Date: Sat, 26 Jul 2014 21:58:25 -0700
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>, linux-crypto@vger.kernel.org,
        linux-kernel@vger.kernel.org
Message-Id: <22C5E3AE-403A-48B7-86EC-F6E4AC42D4A5@gmail.com>
References: <1406383757-1753-1-git-send-email-rickard_strandqvist@spectrumdigital.se>
To: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
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Rickard,

On Jul 26, 2014, at 7:09 AM, Rickard Strandqvist =
<rickard_strandqvist@spectrumdigital.se> wrote:

> Replacing strncpy with strlcpy to avoid strings that lacks null =
terminate.
>=20
> Signed-off-by: Rickard Strandqvist =
<rickard_strandqvist@spectrumdigital.se>
> ---
> crypto/ablkcipher.c |    8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>=20
> diff --git a/crypto/ablkcipher.c b/crypto/ablkcipher.c
> index 40886c4..e446eef 100644
> --- a/crypto/ablkcipher.c
> +++ b/crypto/ablkcipher.c
> @@ -384,8 +384,8 @@ static int crypto_ablkcipher_report(struct sk_buff =
*skb, struct crypto_alg *alg)
> {
> 	struct crypto_report_blkcipher rblkcipher;
>=20
> -	strncpy(rblkcipher.type, "ablkcipher", sizeof(rblkcipher.type));
> -	strncpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: =
"<default>",
> +	strlcpy(rblkcipher.type, "ablkcipher", sizeof(rblkcipher.type));
> +	strlcpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: =
"<default>",
> 		sizeof(rblkcipher.geniv));
>=20
> 	rblkcipher.blocksize =3D alg->cra_blocksize;
> @@ -465,8 +465,8 @@ static int crypto_givcipher_report(struct sk_buff =
*skb, struct crypto_alg *alg)
> {
> 	struct crypto_report_blkcipher rblkcipher;
>=20
> -	strncpy(rblkcipher.type, "givcipher", sizeof(rblkcipher.type));
> -	strncpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: =
"<built-in>",
> +	strlcpy(rblkcipher.type, "givcipher", sizeof(rblkcipher.type));
> +	strlcpy(rblkcipher.geniv, alg->cra_ablkcipher.geniv ?: =
"<built-in>",
> 		sizeof(rblkcipher.geniv));
>=20
> 	rblkcipher.blocksize =3D alg->cra_blocksize;

It looks like all of these patches in the crypto area are introducing =
information leaks, including the one that first made me worry and =
respond. There were no bugs here (unless someone were to introduce a =
crypto method with a name longer than 63 characters), because stncpy =
fills the remainder of the destination with 0.

There are times when strncpy is the right function.

--=20
Mark Rustad, MRustad@gmail.com


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