[PATCH] lib: rsa: Add debug message on algo mismatch

[Simon Glass]

Hi Sean,

On Tue, 16 Feb 2021 at 10:05, Sean Anderson <sean.anderson at seco.com> wrote:
>
>
>
> On 2/16/21 12:01 PM, Wolfgang Denk wrote:
>  > Dear Sean Anderson,
>  >
>  > In message <20210216164016.635125-1-sean.anderson at seco.com> you wrote:
>  >> Currently we fail silently if there is an algorithm mismatch. To help
>  >> distinguish this failure condition.
>  >>
>  >> Signed-off-by: Sean Anderson <sean.anderson at seco.com>
>  >> ---
>  >>
>  >>   lib/rsa/rsa-verify.c | 5 ++++-
>  >>   1 file changed, 4 insertions(+), 1 deletion(-)
>  >>
>  >> diff --git a/lib/rsa/rsa-verify.c b/lib/rsa/rsa-verify.c
>  >> index e34d3293d1..aee76f42d5 100644
>  >> --- a/lib/rsa/rsa-verify.c
>  >> +++ b/lib/rsa/rsa-verify.c
>  >> @@ -447,8 +447,11 @@ static int rsa_verify_with_keynode(struct image_sign_info *info,
>  >>     }
>  >>
>  >>     algo = fdt_getprop(blob, node, "algo", NULL);
>  >> -   if (strcmp(info->name, algo))
>  >> +   if (strcmp(info->name, algo)) {
>  >> +           debug("%s: Wrong algo: have %s, expected %s", __func__,
>  >> +                 info->name, algo);
>  >>             return -EFAULT;
>  >> +   }
>  >
>  > If this is considered an error, should that not be a printf() then
>  > instead of a debug() which users will never see?
>
> I also thought that, but the much of the rest of this file also uses
> debug() to report errors. Perhaps there are security implications? Or
> perhaps it was done to reduce binary size? Simon, can you comment on
> this?

In general should not print messages in the bowels of the code, since
then there is no way to control what is printed. So long as the error
is produced it can be reported and propagated up, and you can document
what the different error codes mean. It also bloats the code to
include strings everywhere.

I suggest adding logging around the return value as it makes it easy
to trace things:

CONFIG_LOG_ERROR_RETURN=y

and return the error with:

   return log_msg_ret("algo", -EFAULT)

Regards,
Simon