[PATCH] lib/rsa: avoid -Wdiscarded-qualifiers

[Tom Rini]

On Mon, Jan 10, 2022 at 09:00:29AM -0600, Alex G. wrote:
> 
> 
> On 1/9/22 8:39 AM, Heinrich Schuchardt wrote:
> > The return type of EVP_PKEY_get0_RSA() is const struct rsa_st *.
> > Our code drops the const qualifier leading to
> > 
> > In file included from tools/lib/rsa/rsa-sign.c:1:
> > ./tools/../lib/rsa/rsa-sign.c: In function ‘rsa_add_verify_data’:
> > ./tools/../lib/rsa/rsa-sign.c:631:13: warning:
> > assignment discards ‘const’ qualifier from pointer target type
> > [-Wdiscarded-qualifiers]
> >    631 |         rsa = EVP_PKEY_get0_RSA(pkey);
> >        |             ^
> > 
> > Add a type conversion.
> > 
> > Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> > ---
> >   lib/rsa/rsa-sign.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/lib/rsa/rsa-sign.c b/lib/rsa/rsa-sign.c
> > index 44f21416ce..3b6e5f0f86 100644
> > --- a/lib/rsa/rsa-sign.c
> > +++ b/lib/rsa/rsa-sign.c
> > @@ -628,7 +628,7 @@ int rsa_add_verify_data(struct image_sign_info *info, void *keydest)
> >   	if (ret)
> >   		goto err_get_pub_key;
> > -	rsa = EVP_PKEY_get0_RSA(pkey);
> > +	rsa = (RSA *)EVP_PKEY_get0_RSA(pkey);
> 
> I think it's the wrong path to discard const qualifiers, whether unwillingly
> or by type punning. I suggest making 'rsa' a "const RSA *" and fixing the
> downstream users to do the same.

So, how do we trigger this warning, exactly?  The line here has been in
place for several releases, but only with fe68a67a5f11 and removing
legacy paths did this become the only option.  Of course, CI isn't
kicking this problem right now.  But CI is Ubuntu 18.04, and while post
v2022.01 we should at least move up to 20.04, I'm guessing this gets hit
with something recent like 20.04, or Debian 11 or what will be Ubuntu
22.04.

Should we take the cast now, and fix this up properly post release?

-- 
Tom
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