[PATCH] g10: Skip signing keys where no secret key is available.

[Patrick Brunschwig]

On 05.02.17 22:31, Daniel Kahn Gillmor wrote:
> From: Simon Arlott <simon at arlott.org>
> 
> * g10/getkey.c (finish_lookup): When requiring PUBKEY_USAGE_SIG, skip
> over keys where no signing key is available.
> 
> --
> 
> This should only be relevant when gpg is required to choose which key
> to sign with -- if verifying signatures, we already know which subkey
> to look at, and indeed gpg doesn't seem to have a problem with this.
> 
> This patch comes from
> https://bugs.gnupg.org/gnupg/file793/sign-fix.patch
> 
> I (dkg) have reviewed and tested it with missing local keys, and it
> makes sense to me as the default behavior.  If the user has the secret
> key for a signing-capable subkey available and the command is --sign,
> it should be used.
> 
> If the user has explicitly specified a subkey that happens to be
> missing (e.g. with the trailing ! for --default-key 0x${FPR}!) then
> this does not override that behavior (the signature will still fail).
> 
> GnuPG-bug-id: 1967
> Debian-bug-id: 834922
> 
> Signed-off-by: Daniel Kahn Gillmor <dkg at fifthhorseman.net>
> ---
>  g10/getkey.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/g10/getkey.c b/g10/getkey.c
> index e39de28ae..d2349ee6c 100644
> --- a/g10/getkey.c
> +++ b/g10/getkey.c
> @@ -3523,6 +3523,13 @@ finish_lookup (kbnode_t keyblock, unsigned int req_usage, int want_exact,
>  	      continue;
>  	    }
>  
> +	  if ((req_usage & PUBKEY_USAGE_SIG) && agent_probe_secret_key (NULL, pk))
> +	    {
> +	      if (DBG_LOOKUP)
> +		log_debug ("\tno secret key for signing\n");
> +	      continue;
> +	    }
> +
>  	  if (DBG_LOOKUP)
>  	    log_debug ("\tsubkey might be fine\n");
>  	  /* In case a key has a timestamp of 0 set, we make sure

Would this patch still issue a "MISSING_KEY" line for --status-fd? If
no, you break existing logic (which for example Enigmail relies on).

-Patrick

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