Re: [PATCH] crypto: rng.c: Cleaning up missing null-terminate in conjunction with strncpy
From: Mark D Rustad
Date: Sat Jul 26 2014 - 22:35:41 EST
On Jul 26, 2014, at 7:18 AM, Rickard Strandqvist <rickard_strandqvist@xxxxxxxxxxxxxxxxxx> wrote:
> Replacing strncpy with strlcpy to avoid strings that lacks null terminate.
> Signed-off-by: Rickard Strandqvist <rickard_strandqvist@xxxxxxxxxxxxxxxxxx>
> crypto/rng.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/crypto/rng.c b/crypto/rng.c
> index e0a25c2..c3d4fb3 100644
> --- a/crypto/rng.c
> +++ b/crypto/rng.c
> @@ -65,7 +65,7 @@ static int crypto_rng_report(struct sk_buff *skb, struct crypto_alg *alg)
> struct crypto_report_rng rrng;
> - strncpy(rrng.type, "rng", sizeof(rrng.type));
> + strlcpy(rrng.type, "rng", sizeof(rrng.type));
> rrng.seedsize = alg->cra_rng.seedsize;
Not to pick on this patch in particular, but you need to be careful about changing strncpy to strlcpy. Although strlcpy ensures termination, it does not prevent information leakage - strncpy ensures that the entire destination buffer is written. When leakage is a concern, it is better to use strncpy and then to store a zero in the last location of the buffer to ensure termination.
These "simple" transformations can be risky - and many of these do not represent any sort of problem when the source is smaller than the destination. I hope information leakage is being considered.
Mark Rustad, MRustad@xxxxxxxxx
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