On Wed, Feb 02, 2022 at 05:52:30AM +0300, Vitaly Chikunov wrote: > Eric, > > On Mon, Jan 31, 2022 at 04:34:13PM -0800, Eric Biggers wrote: > > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > > > Most callers of public_key_verify_signature(), including most indirect > > callers via verify_signature() as well as pkcs7_verify_sig_chain(), > > don't check that public_key_signature::pkey_algo matches > > public_key::pkey_algo. These should always match. > > Why should they match? For the reasons I explain in the rest of the commit message. To summarize: to have a valid signature verification scheme the algorithm must be fixed by the key, and not attacker-controlled. > > public_key_signature is the data prepared to verify the cert's > signature. The cert's signature algorithm could be different from the > public key algorithm defined in the cert itself. They should match only > for self-signed certs. For example, you should be able to sign RSA > public key with ECDSA signature and vice versa. Or 256-bit EC-RDSA with > 512-bit EC-RDSA. This check will prevent this. That has nothing to do with this patch, as this patch is only dealing with the signature. A cert's public key algorithm can be different, and that is fine. > > diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c > > index 4fefb219bfdc8..aba7113d86c76 100644 > > --- a/crypto/asymmetric_keys/public_key.c > > +++ b/crypto/asymmetric_keys/public_key.c > > @@ -325,6 +325,21 @@ int public_key_verify_signature(const struct public_key *pkey, > > BUG_ON(!sig); > > BUG_ON(!sig->s); > > > > + /* > > + * The signature's claimed public key algorithm *must* match the key's > > + * actual public key algorithm. > > + * > > + * Small exception: ECDSA signatures don't specify the curve, but ECDSA > > + * keys do. So the strings can mismatch slightly in that case: > > + * "ecdsa-nist-*" for the key, but "ecdsa" for the signature. > > + */ > > + if (!sig->pkey_algo) > > + return -EINVAL; > > This seem incorrect too, as sig->pkey_algo could be NULL for direct > signature verification calls. For example, for keyctl pkey_verify. We can make it optional if some callers aren't providing it. Of course, such callers wouldn't be able to verify ECDSA signatures. - Eric
