Messages in this thread | | | From | Rickard Strandqvist <> | Date | Sun, 27 Jul 2014 14:14:00 +0200 | Subject | Re: [PATCH] crypto: rng.c: Cleaning up missing null-terminate in conjunction with strncpy |
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2014-07-27 4:35 GMT+02:00 Mark D Rustad <mrustad@gmail.com>: > Rickard, > > On Jul 26, 2014, at 7:18 AM, Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se> wrote: > >> Replacing strncpy with strlcpy to avoid strings that lacks null terminate. >> >> Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se> >> --- >> 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. >
Hi Mark
You clearly have a point there! Information leakage is not something I think about very often otherwise.
It is really unbelievable that C messed up when trying to make a better solution to strcpy. strncpy doing something completely new with zeroes whole size but still does not guarantee a terminating null character. And strlcpy that works great as a replacement for strcpy, but really can not replace strncpy in all cases. Incredibly stupid! :-(
But ok, I'll submit a [Patch V2] with foo[sizeof(foo) - 1] = '\ 0' on all under crypto/ then ?
Kind regards Rickard Strandqvist
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