[PATCH v3 3/4] efi_loader: simplify efi_sigstore_parse_sigdb()

[Ilias Apalodimas]

On Thu, 7 Oct 2021 at 08:54, Heinrich Schuchardt
<heinrich.schuchardt at canonical.com> wrote:
>
>
>
> On 10/6/21 16:05, Ilias Apalodimas wrote:
> > On Wed, 6 Oct 2021 at 16:15, Heinrich Schuchardt
> > <heinrich.schuchardt at canonical.com> wrote:
> >>
> >> On 10/6/21 10:02, Ilias Apalodimas wrote:
> >>> On Wed, 6 Oct 2021 at 10:21, Heinrich Schuchardt
> >>> <heinrich.schuchardt at canonical.com> wrote:
> >>>>
> >>>>
> >>>>
> >>>> On 10/6/21 08:29, Ilias Apalodimas wrote:
> >>>>> On Sun, Oct 03, 2021 at 11:23:19AM +0200, Heinrich Schuchardt wrote:
> >>>>>> Simplify efi_sigstore_parse_sigdb() by using existing functions.
> >>>>>>
> >>>>>> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> >>>>>> ---
> >>>>>> v3:
> >>>>>>        Keep error handling in efi_sigstore_parse_sigdb()
> >>>>>> v2:
> >>>>>>        remove a superfluous check
> >>>>>> ---
> >>>>>>     lib/efi_loader/efi_signature.c | 11 ++---------
> >>>>>>     1 file changed, 2 insertions(+), 9 deletions(-)
> >>>>>>
> >>>>>> diff --git a/lib/efi_loader/efi_signature.c b/lib/efi_loader/efi_signature.c
> >>>>>> index bdd09881fc..97f6dfacd9 100644
> >>>>>> --- a/lib/efi_loader/efi_signature.c
> >>>>>> +++ b/lib/efi_loader/efi_signature.c
> >>>>>> @@ -746,18 +746,11 @@ struct efi_signature_store *efi_sigstore_parse_sigdb(u16 *name)
> >>>>>>        efi_uintn_t db_size;
> >>>>>>        efi_status_t ret;
> >>>>>>
> >>>>>> -    if (!u16_strcmp(name, L"PK") || !u16_strcmp(name, L"KEK")) {
> >>>>>> -            vendor = &efi_global_variable_guid;
> >>>>>> -    } else if (!u16_strcmp(name, L"db") || !u16_strcmp(name, L"dbx")) {
> >>>>>> -            vendor = &efi_guid_image_security_database;
> >>>>>> -    } else {
> >>>>>> -            EFI_PRINT("unknown signature database, %ls\n", name);
> >>>>>> -            return NULL;
> >>>>>> -    }
> >>>>>> +    vendor = efi_auth_var_get_guid(name);
> >>>>>
> >>>>> Should we return NULL if we get back the default guid?
> >>>>
> >>>> efi_sigstore_parse_sigdb() is only called with fixed values of 'name'.
> >>>> So how should this occur?
> >>>
> >>> Bugs that slip through maybe?  I generally prefer being more pedantic
> >>> with security related code
> >>
> >> PK and KEK use efi_global_variable_guid and will be used as argument for
> >> efi_sigstore_parse_sigdb(). Your proposed check would break the code.
> >
> > Yea that's the reason I was asking about efi_auth_var_get_guid().  I
> > would prefer if that returned NULL if the variable is not found
> > instead of the default GUID
>
> As discussed the functions is only called for hardcoded arguments.
>
> Function efi_auth_var_get_guid() parses a list contains dbx, AuditMode,
> DeployedMode. So the check that you propose cannot safeguard against a
> developer misusing efi_sigstore_parse_sigdb().

Yea fair enough, I was trying to think if it would make sense to
re-use it for other variables.


>
> Best regards
>
> Heinrich
>
> >
> > Regards
> > /Ilias
> >>
> >> Best regards
> >>
> >> Heinrich
> >>
> >>>
> >>> Regards
> >>> /Ilias
> >>>>
> >>>> Best regards
> >>>>
> >>>> Heinrich
> >>>>
> >>>>>
> >>>>>>
> >>>>>>        /* retrieve variable data */
> >>>>>>        db_size = 0;
> >>>>>> -    ret = EFI_CALL(efi_get_variable(name, vendor, NULL, &db_size, NULL));
> >>>>>> +    ret = efi_get_variable_int(name, vendor, NULL, &db_size, NULL);
> >>>>>>        if (ret == EFI_NOT_FOUND) {
> >>>>>>                EFI_PRINT("variable, %ls, not found\n", name);
> >>>>>>                sigstore = calloc(sizeof(*sigstore), 1);
> >>>>>> --
> >>>>>> 2.32.0
> >>>>>>
> >>>>>
> >>>>> Regards
> >>>>> /Ilias
> >>>>>
> >>

Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>