linux-kernel - Re: [PATCH] certs: always use secondary keyring first if possible

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Date:   Fri, 8 Jun 2018 16:53:05 +0800
From:   Dave Young <dyoung@...hat.com>
To:     David Howells <dhowells@...hat.com>
Cc:     keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, David Woodhouse <dwmw2@...radead.org>,
        mathew.j.martineau@...ux.intel.com,
        Laura Abbott <labbott@...hat.com>, jwboyer@...hat.com
Subject: Re: [PATCH] certs: always use secondary keyring first if possible

On 06/08/18 at 03:28pm, Dave Young wrote:
> On 12/14/17 at 06:25pm, Dave Young wrote:
> > On 11/18/17 at 12:47pm, Dave Young wrote:
> > > Commit d3bfe84129f6 introduced secondary_trusted_keys keyring, current
> > > users of verify_pkcs7_signature are below:
> > > net/wireless/reg.c : uses its own trusted_keys
> > > kernel/module_signing.c : pass NULL trusted_keys 
> > > crypto/asymmetric_keys/verify_pefile.c : pass NULL trusted_keys
> > > 
> > > For both module and pefile verification, there is no reason to use builtin
> > > keys only. Actually in Fedora kernel module signing code passes 1UL, but
> > > kexec code does not pass 1UL for pefile verification thus we have below bug
> > > https://bugzilla.redhat.com/show_bug.cgi?id=1470995
> > > 
> > > Drop the hard code 1UL checking so that pefile verification can use
> > > secondary keyring as well.
> > > 
> > > Signed-off-by: Dave Young <dyoung@...hat.com>
> > > ---
> > >  certs/system_keyring.c |    2 --
> > >  1 file changed, 2 deletions(-)
> > > 
> > > --- linux-x86.orig/certs/system_keyring.c
> > > +++ linux-x86/certs/system_keyring.c
> > > @@ -229,8 +229,6 @@ int verify_pkcs7_signature(const void *d
> > >  		goto error;
> > >  
> > >  	if (!trusted_keys) {
> > > -		trusted_keys = builtin_trusted_keys;
> > > -	} else if (trusted_keys == (void *)1UL) {
> > >  #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
> > >  		trusted_keys = secondary_trusted_keys;
> > >  #else
> > 
> > Another ping.
> > 
> > If the (-1UL) is really needed, below file need update to use it
> > But I think it is ugly..
> > crypto/asymmetric_keys/verify_pefile.c
> 
> Ping again.  Can anyone response to this issue?
> 
> Let me describe more details about the problem:
> 
> In Fedora kernel there is a patch below which is not upstreamed:
> https://src.fedoraproject.org/rpms/kernel/blob/master/f/Fix-for-module-sig-verification.patch
> 
> It has below changes:
> 
> ---
> diff --git a/kernel/module_signing.c b/kernel/module_signing.c
> index 937c844..d3d6f95 100644
> --- a/kernel/module_signing.c
> +++ b/kernel/module_signing.c
> @@ -81,6 +81,6 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen)
>  	}
> 
>  	return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
> -				      NULL, VERIFYING_MODULE_SIGNATURE,
> +				      (void *)1UL, VERIFYING_MODULE_SIGNATURE,
>  				      NULL, NULL);
>  }
> ---
> 
> Above change is needed because the verify_pkcs7_signature is doing
> below:
> ---
>         if (!trusted_keys) {
>                 trusted_keys = builtin_trusted_keys;
>         } else if (trusted_keys == (void *)1UL) {
> #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
>                 trusted_keys = secondary_trusted_keys;
> #else
>                 trusted_keys = builtin_trusted_keys;
> #endif
>         }
> ---
> 
> The trusted_keys is an argument passed to verify_pkcs7_signature
> function. We can see that users of this function must pass "-1UL"
> as trusted_keys to use secondary keyring.  This "-1UL" is not

I meant to say "1UL" instead of "-1UL"..

> documented and it looks a hardcode api.   Besides of the module
> signing code, actually as I mentioned in the patch log kexec/kdump
> also need passing "-1UL" to use the secondary keyring.
> 
> But why do we need that hack?  If I understand it correctly
> if use secondary then builtin can still be used, see commit log
> of d3bfe84129f65e0af2450743ebdab33d161d01c9:
>     If the secondary keyring is enabled, a link is created from that to
>     .builtin_trusted_keys so that the the latter will automatically be searched
>     too if the secondary keyring is searched.
> 
> So why not directly use secondary in case trusted_keys == NULL?
> 
> I'm not familar with the certs/keyring code, if I'm wrong please
> correct me.
> 
> --
> Thanks
> Dave
>