Jeff King venit, vidit, dixit 14.06.2016 13:20:
> On Tue, Jun 14, 2016 at 01:11:19PM +0200, Michael J Gruber wrote:
>
>> When we create a signature, it may happen that gpg returns with
>> "success" but not with an actual detached signature on stdout.
>>
>> Check for the correct header to catch these cases better.
>
> Seems like a reasonable idea.
>
> I do worry that checking for PGP_SIGNATURE is a little fragile, though.
> We currently let you sign with gpgsm, for example, and I think this
> would break it (the verification side is not great because we don't
> recognize gpgsm headers, but this feels like a step backwards).
>
> That wouldn't be too hard to work around with a "is this a signature"
> function that checks both types.
>
>> diff --git a/gpg-interface.c b/gpg-interface.c
>> index c4b1e8c..664796f 100644
>> --- a/gpg-interface.c
>> +++ b/gpg-interface.c
>> @@ -185,7 +185,7 @@ int sign_buffer(struct strbuf *buffer, struct strbuf
>> *signature, const char *sig
>>
>> sigchain_pop(SIGPIPE);
>>
>> - if (finish_command(&gpg) || !len || len < 0)
>> + if (finish_command(&gpg) || !len || len < 0 || strncmp(signature->buf,
>> PGP_SIGNATURE, strlen(PGP_SIGNATURE)))
>> return error(_("gpg failed to sign the data"));
>
> I think your strncmp is better spelled:
>
> starts_with(signature->buf, PGP_SIGNATURE);
>
> The check for "!len" is redundant now. I think you could drop "len < 0"
> as well (and in fact, drop the "len" variable entirely), as in the error
> case we'd simply have an empty signature->len.
>
> Your patch effectively swaps out "did we get any data" for "did we get
> the data we expect", which is what those "len" checks were doing.
>
> -Peff
>
My patch actually makes several tests fail, sorry. (I did check before
that I can still create signatures...) Maybe my offset in buf is wrong.
starts_with, yes.
Can't check any further now, sorry. But we do check for the
PGP_SIGNATURE in our signed objects anyways. So I feel that we can either
- tighthen the check for valid gpg signatures
or
- make our signature interface completely pluggable.
We can't have it both ways, but at least things are localised in
gpg-interface.c now.
The proposed patch is just some consistency check that does not rely on
gpg.program itself(!), or else we could simply call verify.
Michael
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