Re: [PATCH v5 05/11] crypto: qce: skcipher: Return error for zero length messages

[Thara Gopinath]

Hi Eric,

On 2/4/21 5:48 PM, Eric Biggers wrote:
> On Thu, Feb 04, 2021 at 04:43:53PM -0500, Thara Gopinath wrote:
> > Crypto engine BAM dma does not support 0 length data. Return unsupported
> > if zero length messages are passed for transformation.
> >
> > Signed-off-by: Thara Gopinath <thara.gopinath@xxxxxxxxxx>
> > ---
> >   drivers/crypto/qce/skcipher.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/crypto/qce/skcipher.c b/drivers/crypto/qce/skcipher.c
> > index de1f37ed4ee6..331b3c3a5b59 100644
> > --- a/drivers/crypto/qce/skcipher.c
> > +++ b/drivers/crypto/qce/skcipher.c
> > @@ -8,6 +8,7 @@
> >   #include <linux/interrupt.h>
> >   #include <linux/moduleparam.h>
> >   #include <linux/types.h>
> > +#include <linux/errno.h>
> >   #include <crypto/aes.h>
> >   #include <crypto/internal/des.h>
> >   #include <crypto/internal/skcipher.h>
> > @@ -260,6 +261,10 @@ static int qce_skcipher_crypt(struct skcipher_request *req, int encrypt)
> >   	rctx->flags |= encrypt ? QCE_ENCRYPT : QCE_DECRYPT;
> >   	keylen = IS_XTS(rctx->flags) ? ctx->enc_keylen >> 1 : ctx->enc_keylen;
> >   
> > +	/* CE does not handle 0 length messages */
> > +	if (!req->cryptlen)
> > +		return -EOPNOTSUPP;
> > +
>
> For the algorithms in question, the correct behavior is to return 0.

What do you mean? The driver should return a 0 ?

> Aren't the tests catching that difference?

I was anyways planning on sending an email to the list with these 
queries. But since you asked,  these are my observations with fuzz 
testing which I have been doing quite a bit now (I am also working on 
adding a few qualcomm AEAD algorithms support in mainline).

- if the generic algorithm supports 0 length messages and the 
transformation I am testing does not, the test framework throws an error 
and stops.
- key support mismatch between the generic algorithm vs my algorithm 
/engine also does the same thing.For eg, Qualcomm CE engine does not 
support any three keys being same for triple des algorithms. Where as a 
two key 3des is a valid scenario for generic algorithm(k1=k3). Another 
example is hardware engine not supporting AES192.

How are these scenarios usually handled ? Why not allow the test 
framework to proceed with the testing if the algorithm does not support 
a particular scenario ?

> - Eric
--
Warm Regards
Thara