[PATCH] lib/crypto: Enable more algorithms in cert verification

[Ilias Apalodimas]

Hi Heinrich,

On Tue, 18 Jan 2022 at 18:22, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> On 1/18/22 15:03, Ilias Apalodimas wrote:
> > Hi Heinrich,
> >
> >>>>> -         info.checksum = image_get_checksum_algo("sha256,rsa2048");
> >
> > [...]
> >
> >>>>> -         info.name = "sha256,rsa2048";
> >>>>> - } else {
> >>>>> -         pr_warn("unknown msg digest algo: %s\n", sig->hash_algo);
> >>>>> + if (strcmp(sig->pkey_algo, "rsa")) {
> >>>>> +         pr_err("Encryption is not RSA: %s\n", sig->pkey_algo);
> >>>>>                   return -ENOPKG;
> >>>>>           }
> >>>>> + ret = snprintf(algo, sizeof(algo), "%s,%s%d", sig->hash_algo,
> >>>>> +                sig->pkey_algo, sig->s_size * 8);
> >>
> >> How do we ensure that the unsafe SHA1 algorithm is not used?
> >
> > We don't,  but the current code allows it as well.  Should we enforce this
> > from U-Boot  though?  The spec doesn't forbid it as far as I remember
>
> Collisions for SHA1 have been first created successfully in 2017.
>
> It is feasible to create two different EFI binaries with the same SHA1.
> One will be reviewed and signed. After copying the signature to the
> other one it will happily boot on U-Boot. Ouch. This is exactly what
> signatures are meant to avoid.
>
> We must not accept SHA1 for signatures.

Right, but is this the right place to do it? This is function to
verify signatures.  Isn't it better to keep this as is and then
explicitly deny adding sha1 hashed keys into db?

Cheers
/Ilias
>
> Best regards
>
> Heinrich
>
> >
> > Regards
> > /Ilias
> >>
> >> Best regards
> >>
> >> Heinrich
> >>
> >>>>
> >>>> I'm not sure that this naming rule, in particular the latter part, will
> >>>> always hold in the future while all the existing algo's observe it.
> >>>> (Maybe we need some note somewhere?)
> >>>
> >>> The if a few lines below will shield us and return -EINVAL.  How about
> >>> adding an error message there?
> >>>
> >>> Cheers
> >>> /Ilias
> >>>>
> >>>> -Takahiro Akashi
> >>>>
> >>>>> +
> >>>>> + if (ret >= sizeof(algo))
> >>>>> +         return -EINVAL;
> >>>>> +
> >>>>> + info.checksum = image_get_checksum_algo((const char *)algo);
> >>>>> + info.name = (const char *)algo;
> >>>>>           info.crypto = image_get_crypto_algo(info.name);
> >>>>> - if (IS_ERR(info.checksum) || IS_ERR(info.crypto))
> >>>>> + if (!info.checksum || !info.crypto)
> >>>>>                   return -ENOPKG;
> >>>>>
> >>>>>           info.key = pkey->key;
> >>>>> --
> >>>>> 2.30.2
> >>>>>
> >>
>