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gpg: New import and keyserver option "self-sigs-only"

* g10/options.h (IMPORT_SELF_SIGS_ONLY): New.
* g10/import.c (parse_import_options): Add option "self-sigs-only".
(read_block): Handle that option.
--

This option is intended to help against importing keys with many bogus
key-signatures.  It has obvious drawbacks and is not a bullet-proof
solution because a self-signature can also be faked and would be
detected only later.

GnuPG-bug-id: 4591
Signed-off-by: Werner Koch <wk@gnupg.org>
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dd9jn committed Jul 1, 2019
1 parent 894b72d commit 2e349bb6173789e0e9e42c32873d89c7bc36cea4
Showing with 48 additions and 3 deletions.
  1. +8 −0 doc/gpg.texi
  2. +39 −3 g10/import.c
  3. +1 −0 g10/options.h
@@ -2341,6 +2341,14 @@ opposite meaning. The options are:
can be used to update only the subkeys or other non-user id related
information.

@item self-sigs-only
Accept only self-signatures while importing a key. All other
key-signatures are skipped at an early import stage. This option
can be used with @code{keyserver-options} to mitigate attempts to
flood a key with bogus signatures from a keyserver. The drawback is
that all other valid key-signatures, as required by the Web of Trust
are also not imported.

@item repair-keys
After import, fix various problems with the
keys. For example, this reorders signatures, and strips duplicate
@@ -190,7 +190,10 @@ parse_import_options(char *str,unsigned int *options,int noisy)
N_("remove as much as possible from key after import")},

{"import-drop-uids", IMPORT_DROP_UIDS, NULL,
N_("Do not import user id or attribute packets")},
N_("do not import user id or attribute packets")},

{"self-sigs-only", IMPORT_SELF_SIGS_ONLY, NULL,
N_("ignore key-signatures which are not self-signatures")},

{"import-export", IMPORT_EXPORT, NULL,
N_("run import filters and export key immediately")},
@@ -861,6 +864,8 @@ read_block( IOBUF a, unsigned int options,
PACKET *pkt;
kbnode_t root = NULL;
int in_cert, in_v3key, skip_sigs;
u32 keyid[2];
unsigned int dropped_nonselfsigs = 0;

*r_v3keys = 0;

@@ -983,16 +988,43 @@ read_block( IOBUF a, unsigned int options,
init_packet(pkt);
break;

case PKT_SIGNATURE:
if (!in_cert)
goto x_default;
if (!(options & IMPORT_SELF_SIGS_ONLY))
goto x_default;
if (pkt->pkt.signature->keyid[0] == keyid[0]
&& pkt->pkt.signature->keyid[1] == keyid[1])
{ /* This is likely a self-signature. We import this one.
* Eventually we should use the ISSUER_FPR to compare
* self-signatures, but that will work only for v5 keys
* which are currently not even deployed.
* Note that we do not do any crypto verify here because
* that would defeat this very mitigation of DoS by
* importing a key with a huge amount of faked
* key-signatures. A verification will be done later in
* the processing anyway. Here we want a cheap an early
* way to drop non-self-signatures. */
goto x_default;
}
/* Skip this signature. */
dropped_nonselfsigs++;
free_packet (pkt, &parsectx);
init_packet(pkt);
break;

case PKT_PUBLIC_KEY:
case PKT_SECRET_KEY:
if (in_cert ) /* Store this packet. */
if (in_cert) /* Store this packet. */
{
*pending_pkt = pkt;
pkt = NULL;
goto ready;
}
in_cert = 1;
/* fall through */
keyid_from_pk (pkt->pkt.public_key, keyid);
goto x_default;

default:
x_default:
if (in_cert && valid_keyblock_packet (pkt->pkttype))
@@ -1021,6 +1053,10 @@ read_block( IOBUF a, unsigned int options,
free_packet (pkt, &parsectx);
deinit_parse_packet (&parsectx);
xfree( pkt );
if (!rc && dropped_nonselfsigs && opt.verbose)
log_info ("key %s: number of dropped non-self-signatures: %u\n",
keystr (keyid), dropped_nonselfsigs);

return rc;
}

@@ -363,6 +363,7 @@ EXTERN_UNLESS_MAIN_MODULE int memory_stat_debug_mode;
#define IMPORT_REPAIR_KEYS (1<<11)
#define IMPORT_DRY_RUN (1<<12)
#define IMPORT_DROP_UIDS (1<<13)
#define IMPORT_SELF_SIGS_ONLY (1<<14)

#define EXPORT_LOCAL_SIGS (1<<0)
#define EXPORT_ATTRIBUTES (1<<1)

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