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List:       linux-api
Subject:    Re: [PATCH v6 6/6] crypto: AF_ALG - add support for key_id
From:       Tadeusz Struk <tadeusz.struk () intel ! com>
Date:       2016-05-31 17:44:03
Message-ID: 304aa8f1-ef22-3f2d-53e5-3c020f7ceb40 () intel ! com
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Hi Mat,
On 05/25/2016 05:45 PM, Mat Martineau wrote:
> 
> On Sat, 14 May 2016, Tadeusz Struk wrote:
> 
> > diff --git a/crypto/algif_akcipher.c b/crypto/algif_akcipher.c
> > index e00793d..6733df1 100644
> > --- a/crypto/algif_akcipher.c
> > +++ b/crypto/algif_akcipher.c
> > +static int asym_key_verify(const struct key *key, struct akcipher_request *req)
> > +{
> > +    struct public_key_signature sig;
> > +    char *src = NULL, *in;
> > +    int ret;
> > +
> > +    if (!sg_is_last(req->src)) {
> > +        src = kmalloc(req->src_len, GFP_KERNEL);
> > +        if (!src)
> > +            return -ENOMEM;
> > +        scatterwalk_map_and_copy(src, req->src, 0, req->src_len, 0);
> > +        in = src;
> > +    } else {
> > +        in = sg_virt(req->src);
> > +    }
> > +    sig.pkey_algo = "rsa";
> > +    sig.encoding = "pkcs1";
> > +    /* Need to find a way to pass the hash param */
> 
> Are you referring to sig.digest here? It looks like you will hit a BUG_ON() in \
> public_key_verify_signature() if sig.digest is 0. However, sig.digest is unlikely \
> to be 0 because the struct is not cleared - should fix this, since \
> public_key_verify_signature() will try to follow that random pointer. 

Right, I need to have a local buffer for the digest here.

> > +    sig.hash_algo = "sha1";
> > +    sig.digest_size = 20;
> > +    sig.s_size = req->src_len;
> > +    sig.s = src;
> > +    ret = verify_signature(key, NULL, &sig);
> 
> Is the idea to write the signature to the socket, and then read out the expected \
> digest (the digest comparison being done elsewhere)? Is that something that will be \
> supported by a future hardware asymmetric key subtype?

After the verify operation the output will be copied to the user,
and the user needs to verify it.

> 
> verify_signature() ends up calling public_key_verify_signature(), which currently \
> expects to get both the digest and signature as input and returns an error if \
> verification fails. The output of crypto_akcipher_verify() is discarded before \
> public_key_verify_signature() returns so nothing ends up in req->dst to read from \
> the socket. 
> ALG_OP_VERIFY should behave the same whether using ALG_SET_PUBKEY or \
> ALG_SET_PUBKEY_ID, and they aren't right now. 
> If sig.digest is 0, verify_signature() could return the expected digest in the sig \
> structure and skip the digest comparison it currently does. Then that data could be \
> packaged up in req as if crypto_akcipher_verify() had been called. I don't know if \
> this change confuses the semantics of verify_signature() too much, maybe a new \
> function is required with all the requisite plumbing to the asymmetric key subtype. \
> 

We need to copy output to the user to verify because we don't have it.
That will be consistent for both ALG_SET_PUBKEY and ALG_SET_PUBKEY_ID.
Thanks for your comments and sorry for the delayed response. I'll will send v7 soon.
-- 
TS
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