Re: [PATCH] crypto: blkcipher: prefer strlcpy to strncpy

From: Eric Biggers
Date: Tue May 29 2018 - 12:34:06 EST


On Mon, May 28, 2018 at 10:44:43PM -0700, Nick Desaulniers wrote:
> Fixes stringop-truncation warnings from gcc-8.
>
> Signed-off-by: Nick Desaulniers <nick.desaulniers@xxxxxxxxx>
> ---
> crypto/ablkcipher.c | 8 ++++----
> crypto/blkcipher.c | 4 ++--
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/crypto/ablkcipher.c b/crypto/ablkcipher.c
> index d880a48..e38867f 100644
> --- a/crypto/ablkcipher.c
> +++ b/crypto/ablkcipher.c
> @@ -370,8 +370,8 @@ static int crypto_ablkcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
> {
> struct crypto_report_blkcipher rblkcipher;
>
> - 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));
>
> rblkcipher.blocksize = alg->cra_blocksize;
> @@ -444,8 +444,8 @@ static int crypto_givcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
> {
> struct crypto_report_blkcipher rblkcipher;
>
> - 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));
>
> rblkcipher.blocksize = alg->cra_blocksize;
> diff --git a/crypto/blkcipher.c b/crypto/blkcipher.c
> index 01c0d4a..ee88e48 100644
> --- a/crypto/blkcipher.c
> +++ b/crypto/blkcipher.c
> @@ -509,8 +509,8 @@ static int crypto_blkcipher_report(struct sk_buff *skb, struct crypto_alg *alg)
> {
> struct crypto_report_blkcipher rblkcipher;
>
> - strncpy(rblkcipher.type, "blkcipher", sizeof(rblkcipher.type));
> - strncpy(rblkcipher.geniv, alg->cra_blkcipher.geniv ?: "<default>",
> + strlcpy(rblkcipher.type, "blkcipher", sizeof(rblkcipher.type));
> + strlcpy(rblkcipher.geniv, alg->cra_blkcipher.geniv ?: "<default>",
> sizeof(rblkcipher.geniv));
>
> rblkcipher.blocksize = alg->cra_blocksize;
> --
> 2.7.4
>

Hi Nick, this patch is wrong. The 'struct crypto_report_blkcipher' is being
copied to userspace via netlink, so all bytes of it must be initialized.
strncpy() does this but strlcpy() does not.

I noticed that you're sending out some other patches replacing strncpy() with
strlcpy() too. Can you please double check them for this same bug?

Thanks,

- Eric