зеркало из https://github.com/microsoft/git.git
gpg-interface: prefer check_signature() for GPG verification
This commit refactors the use of verify_signed_buffer() outside of gpg-interface.c to use check_signature() instead. It also turns verify_signed_buffer() into a file-local function since it's now only invoked internally by check_signature(). There were previously two globally scoped functions used in different parts of Git to perform GPG signature verification: verify_signed_buffer() and check_signature(). Now only check_signature() is used. The verify_signed_buffer() function doesn't guard against duplicate signatures as described by Michał Górny [1]. Instead it only ensures a non-erroneous exit code from GPG and the presence of at least one GOODSIG status field. This stands in contrast with check_signature() that returns an error if more than one signature is encountered. The lower degree of verification makes the use of verify_signed_buffer() problematic if callers don't parse and validate the various parts of the GPG status message themselves. And processing these messages seems like a task that should be reserved to gpg-interface.c with the function check_signature(). Furthermore, the use of verify_signed_buffer() makes it difficult to introduce new functionality that relies on the content of the GPG status lines. Now all operations that does signature verification share a single entry point to gpg-interface.c. This makes it easier to propagate changed or additional functionality in GPG signature verification to all parts of Git, without having odd edge-cases that don't perform the same degree of verification. [1] https://dev.gentoo.org/~mgorny/articles/attack-on-git-signature-verification.html Signed-off-by: Hans Jerry Illikainen <hji@dyntopia.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Hans Jerry Illikainen
Junio C Hamano
Родитель
f1e3df3169
Коммит
6794898198
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@ -494,6 +494,7 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
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enum object_type type;
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unsigned long size, len;
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char *buf = read_object_file(oid, &type, &size);
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struct signature_check sigc = { 0 };
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struct strbuf sig = STRBUF_INIT;
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if (!buf || type != OBJ_TAG)
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@ -502,10 +503,12 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
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if (size == len)
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; /* merely annotated */
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else if (verify_signed_buffer(buf, len, buf + len, size - len, &sig, NULL)) {
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if (!sig.len)
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strbuf_addstr(&sig, "gpg verification failed.\n");
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}
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else if (check_signature(buf, len, buf + len, size - len, &sigc) &&
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!sigc.gpg_output)
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strbuf_addstr(&sig, "gpg verification failed.\n");
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else
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strbuf_addstr(&sig, sigc.gpg_output);
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signature_check_clear(&sigc);
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if (!tag_number++) {
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fmt_tag_signature(&tagbuf, &sig, buf, len);
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@ -256,6 +256,55 @@ error:
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FREE_AND_NULL(sigc->key);
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}
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static int verify_signed_buffer(const char *payload, size_t payload_size,
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const char *signature, size_t signature_size,
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struct strbuf *gpg_output,
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struct strbuf *gpg_status)
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{
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struct child_process gpg = CHILD_PROCESS_INIT;
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struct gpg_format *fmt;
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struct tempfile *temp;
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int ret;
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struct strbuf buf = STRBUF_INIT;
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temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
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if (!temp)
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return error_errno(_("could not create temporary file"));
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if (write_in_full(temp->fd, signature, signature_size) < 0 ||
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close_tempfile_gently(temp) < 0) {
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error_errno(_("failed writing detached signature to '%s'"),
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temp->filename.buf);
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delete_tempfile(&temp);
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return -1;
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}
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fmt = get_format_by_sig(signature);
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if (!fmt)
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BUG("bad signature '%s'", signature);
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argv_array_push(&gpg.args, fmt->program);
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argv_array_pushv(&gpg.args, fmt->verify_args);
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argv_array_pushl(&gpg.args,
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"--status-fd=1",
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"--verify", temp->filename.buf, "-",
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NULL);
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if (!gpg_status)
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gpg_status = &buf;
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sigchain_push(SIGPIPE, SIG_IGN);
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ret = pipe_command(&gpg, payload, payload_size,
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gpg_status, 0, gpg_output, 0);
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sigchain_pop(SIGPIPE);
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delete_tempfile(&temp);
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ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
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strbuf_release(&buf); /* no matter it was used or not */
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return ret;
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}
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int check_signature(const char *payload, size_t plen, const char *signature,
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size_t slen, struct signature_check *sigc)
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{
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@ -418,51 +467,3 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
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return 0;
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}
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int verify_signed_buffer(const char *payload, size_t payload_size,
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const char *signature, size_t signature_size,
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struct strbuf *gpg_output, struct strbuf *gpg_status)
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{
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struct child_process gpg = CHILD_PROCESS_INIT;
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struct gpg_format *fmt;
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struct tempfile *temp;
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int ret;
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struct strbuf buf = STRBUF_INIT;
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temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
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if (!temp)
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return error_errno(_("could not create temporary file"));
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if (write_in_full(temp->fd, signature, signature_size) < 0 ||
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close_tempfile_gently(temp) < 0) {
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error_errno(_("failed writing detached signature to '%s'"),
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temp->filename.buf);
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delete_tempfile(&temp);
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return -1;
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}
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fmt = get_format_by_sig(signature);
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if (!fmt)
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BUG("bad signature '%s'", signature);
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argv_array_push(&gpg.args, fmt->program);
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argv_array_pushv(&gpg.args, fmt->verify_args);
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argv_array_pushl(&gpg.args,
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"--status-fd=1",
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"--verify", temp->filename.buf, "-",
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NULL);
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if (!gpg_status)
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gpg_status = &buf;
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sigchain_push(SIGPIPE, SIG_IGN);
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ret = pipe_command(&gpg, payload, payload_size,
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gpg_status, 0, gpg_output, 0);
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sigchain_pop(SIGPIPE);
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delete_tempfile(&temp);
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ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
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strbuf_release(&buf); /* no matter it was used or not */
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return ret;
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}
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@ -54,15 +54,6 @@ size_t parse_signature(const char *buf, size_t size);
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int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
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const char *signing_key);
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/*
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* Run "gpg" to see if the payload matches the detached signature.
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* gpg_output, when set, receives the diagnostic output from GPG.
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* gpg_status, when set, receives the status output from GPG.
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*/
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int verify_signed_buffer(const char *payload, size_t payload_size,
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const char *signature, size_t signature_size,
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struct strbuf *gpg_output, struct strbuf *gpg_status);
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int git_gpg_config(const char *, const char *, void *);
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void set_signing_key(const char *);
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const char *get_signing_key(void);
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34
log-tree.c
34
log-tree.c
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@ -449,22 +449,21 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
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{
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struct strbuf payload = STRBUF_INIT;
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struct strbuf signature = STRBUF_INIT;
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struct strbuf gpg_output = STRBUF_INIT;
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struct signature_check sigc = { 0 };
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int status;
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if (parse_signed_commit(commit, &payload, &signature) <= 0)
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goto out;
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status = verify_signed_buffer(payload.buf, payload.len,
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signature.buf, signature.len,
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&gpg_output, NULL);
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if (status && !gpg_output.len)
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strbuf_addstr(&gpg_output, "No signature\n");
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show_sig_lines(opt, status, gpg_output.buf);
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status = check_signature(payload.buf, payload.len, signature.buf,
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signature.len, &sigc);
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if (status && !sigc.gpg_output)
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show_sig_lines(opt, status, "No signature\n");
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else
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show_sig_lines(opt, status, sigc.gpg_output);
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signature_check_clear(&sigc);
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out:
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strbuf_release(&gpg_output);
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strbuf_release(&payload);
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strbuf_release(&signature);
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}
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@ -497,8 +496,9 @@ static int show_one_mergetag(struct commit *commit,
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struct object_id oid;
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struct tag *tag;
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struct strbuf verify_message;
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struct signature_check sigc = { 0 };
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int status, nth;
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size_t payload_size, gpg_message_offset;
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size_t payload_size;
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hash_object_file(the_hash_algo, extra->value, extra->len,
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type_name(OBJ_TAG), &oid);
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@ -520,19 +520,19 @@ static int show_one_mergetag(struct commit *commit,
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else
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strbuf_addf(&verify_message,
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"parent #%d, tagged '%s'\n", nth + 1, tag->tag);
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gpg_message_offset = verify_message.len;
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payload_size = parse_signature(extra->value, extra->len);
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status = -1;
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if (extra->len > payload_size) {
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/* could have a good signature */
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if (!verify_signed_buffer(extra->value, payload_size,
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extra->value + payload_size,
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extra->len - payload_size,
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&verify_message, NULL))
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status = 0; /* good */
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else if (verify_message.len <= gpg_message_offset)
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status = check_signature(extra->value, payload_size,
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extra->value + payload_size,
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extra->len - payload_size, &sigc);
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if (sigc.gpg_output)
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strbuf_addstr(&verify_message, sigc.gpg_output);
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else
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strbuf_addstr(&verify_message, "No signature\n");
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signature_check_clear(&sigc);
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/* otherwise we couldn't verify, which is shown as bad */
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}
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