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![Hans Jerry Illikainen](/assets/img/avatar_default.png)
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>
470 lines
12 KiB
C
470 lines
12 KiB
C
#include "cache.h"
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#include "config.h"
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#include "run-command.h"
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#include "strbuf.h"
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#include "gpg-interface.h"
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#include "sigchain.h"
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#include "tempfile.h"
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static char *configured_signing_key;
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static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
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struct gpg_format {
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const char *name;
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const char *program;
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const char **verify_args;
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const char **sigs;
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};
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static const char *openpgp_verify_args[] = {
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"--keyid-format=long",
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NULL
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};
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static const char *openpgp_sigs[] = {
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"-----BEGIN PGP SIGNATURE-----",
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"-----BEGIN PGP MESSAGE-----",
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NULL
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};
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static const char *x509_verify_args[] = {
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NULL
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};
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static const char *x509_sigs[] = {
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"-----BEGIN SIGNED MESSAGE-----",
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NULL
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};
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static struct gpg_format gpg_format[] = {
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{ .name = "openpgp", .program = "gpg",
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.verify_args = openpgp_verify_args,
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.sigs = openpgp_sigs
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},
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{ .name = "x509", .program = "gpgsm",
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.verify_args = x509_verify_args,
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.sigs = x509_sigs
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},
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};
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static struct gpg_format *use_format = &gpg_format[0];
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static struct gpg_format *get_format_by_name(const char *str)
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{
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int i;
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for (i = 0; i < ARRAY_SIZE(gpg_format); i++)
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if (!strcmp(gpg_format[i].name, str))
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return gpg_format + i;
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return NULL;
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}
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static struct gpg_format *get_format_by_sig(const char *sig)
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{
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int i, j;
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for (i = 0; i < ARRAY_SIZE(gpg_format); i++)
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for (j = 0; gpg_format[i].sigs[j]; j++)
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if (starts_with(sig, gpg_format[i].sigs[j]))
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return gpg_format + i;
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return NULL;
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}
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void signature_check_clear(struct signature_check *sigc)
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{
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FREE_AND_NULL(sigc->payload);
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FREE_AND_NULL(sigc->gpg_output);
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FREE_AND_NULL(sigc->gpg_status);
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FREE_AND_NULL(sigc->signer);
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FREE_AND_NULL(sigc->key);
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FREE_AND_NULL(sigc->fingerprint);
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FREE_AND_NULL(sigc->primary_key_fingerprint);
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}
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/* An exclusive status -- only one of them can appear in output */
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#define GPG_STATUS_EXCLUSIVE (1<<0)
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/* The status includes key identifier */
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#define GPG_STATUS_KEYID (1<<1)
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/* The status includes user identifier */
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#define GPG_STATUS_UID (1<<2)
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/* The status includes key fingerprints */
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#define GPG_STATUS_FINGERPRINT (1<<3)
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/* The status includes trust level */
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#define GPG_STATUS_TRUST_LEVEL (1<<4)
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/* Short-hand for standard exclusive *SIG status with keyid & UID */
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#define GPG_STATUS_STDSIG (GPG_STATUS_EXCLUSIVE|GPG_STATUS_KEYID|GPG_STATUS_UID)
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static struct {
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char result;
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const char *check;
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unsigned int flags;
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} sigcheck_gpg_status[] = {
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{ 'G', "GOODSIG ", GPG_STATUS_STDSIG },
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{ 'B', "BADSIG ", GPG_STATUS_STDSIG },
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{ 'E', "ERRSIG ", GPG_STATUS_EXCLUSIVE|GPG_STATUS_KEYID },
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{ 'X', "EXPSIG ", GPG_STATUS_STDSIG },
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{ 'Y', "EXPKEYSIG ", GPG_STATUS_STDSIG },
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{ 'R', "REVKEYSIG ", GPG_STATUS_STDSIG },
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{ 0, "VALIDSIG ", GPG_STATUS_FINGERPRINT },
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{ 0, "TRUST_", GPG_STATUS_TRUST_LEVEL },
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};
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static struct {
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const char *key;
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enum signature_trust_level value;
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} sigcheck_gpg_trust_level[] = {
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{ "UNDEFINED", TRUST_UNDEFINED },
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{ "NEVER", TRUST_NEVER },
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{ "MARGINAL", TRUST_MARGINAL },
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{ "FULLY", TRUST_FULLY },
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{ "ULTIMATE", TRUST_ULTIMATE },
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};
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static void replace_cstring(char **field, const char *line, const char *next)
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{
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free(*field);
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if (line && next)
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*field = xmemdupz(line, next - line);
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else
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*field = NULL;
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}
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static int parse_gpg_trust_level(const char *level,
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enum signature_trust_level *res)
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{
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size_t i;
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for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_trust_level); i++) {
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if (!strcmp(sigcheck_gpg_trust_level[i].key, level)) {
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*res = sigcheck_gpg_trust_level[i].value;
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return 0;
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}
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}
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return 1;
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}
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static void parse_gpg_output(struct signature_check *sigc)
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{
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const char *buf = sigc->gpg_status;
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const char *line, *next;
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int i, j;
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int seen_exclusive_status = 0;
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/* Iterate over all lines */
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for (line = buf; *line; line = strchrnul(line+1, '\n')) {
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while (*line == '\n')
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line++;
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if (!*line)
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break;
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/* Skip lines that don't start with GNUPG status */
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if (!skip_prefix(line, "[GNUPG:] ", &line))
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continue;
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/* Iterate over all search strings */
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for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) {
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if (skip_prefix(line, sigcheck_gpg_status[i].check, &line)) {
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/*
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* GOODSIG, BADSIG etc. can occur only once for
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* each signature. Therefore, if we had more
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* than one then we're dealing with multiple
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* signatures. We don't support them
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* currently, and they're rather hard to
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* create, so something is likely fishy and we
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* should reject them altogether.
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*/
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if (sigcheck_gpg_status[i].flags & GPG_STATUS_EXCLUSIVE) {
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if (seen_exclusive_status++)
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goto error;
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}
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if (sigcheck_gpg_status[i].result)
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sigc->result = sigcheck_gpg_status[i].result;
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/* Do we have key information? */
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if (sigcheck_gpg_status[i].flags & GPG_STATUS_KEYID) {
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next = strchrnul(line, ' ');
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replace_cstring(&sigc->key, line, next);
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/* Do we have signer information? */
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if (*next && (sigcheck_gpg_status[i].flags & GPG_STATUS_UID)) {
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line = next + 1;
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next = strchrnul(line, '\n');
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replace_cstring(&sigc->signer, line, next);
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}
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}
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/* Do we have trust level? */
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if (sigcheck_gpg_status[i].flags & GPG_STATUS_TRUST_LEVEL) {
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/*
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* GPG v1 and v2 differs in how the
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* TRUST_ lines are written. Some
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* trust lines contain no additional
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* space-separated information for v1.
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*/
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size_t trust_size = strcspn(line, " \n");
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char *trust = xmemdupz(line, trust_size);
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if (parse_gpg_trust_level(trust, &sigc->trust_level)) {
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free(trust);
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goto error;
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}
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free(trust);
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}
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/* Do we have fingerprint? */
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if (sigcheck_gpg_status[i].flags & GPG_STATUS_FINGERPRINT) {
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const char *limit;
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char **field;
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next = strchrnul(line, ' ');
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replace_cstring(&sigc->fingerprint, line, next);
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/*
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* Skip interim fields. The search is
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* limited to the same line since only
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* OpenPGP signatures has a field with
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* the primary fingerprint.
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*/
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limit = strchrnul(line, '\n');
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for (j = 9; j > 0; j--) {
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if (!*next || limit <= next)
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break;
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line = next + 1;
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next = strchrnul(line, ' ');
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}
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field = &sigc->primary_key_fingerprint;
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if (!j) {
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next = strchrnul(line, '\n');
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replace_cstring(field, line, next);
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} else {
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replace_cstring(field, NULL, NULL);
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}
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}
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break;
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}
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}
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}
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return;
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error:
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sigc->result = 'E';
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/* Clear partial data to avoid confusion */
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FREE_AND_NULL(sigc->primary_key_fingerprint);
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FREE_AND_NULL(sigc->fingerprint);
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FREE_AND_NULL(sigc->signer);
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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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struct strbuf gpg_output = STRBUF_INIT;
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struct strbuf gpg_status = STRBUF_INIT;
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int status;
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sigc->result = 'N';
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sigc->trust_level = -1;
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status = verify_signed_buffer(payload, plen, signature, slen,
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&gpg_output, &gpg_status);
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if (status && !gpg_output.len)
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goto out;
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sigc->payload = xmemdupz(payload, plen);
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sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
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sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
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parse_gpg_output(sigc);
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status |= sigc->result != 'G';
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status |= sigc->trust_level < configured_min_trust_level;
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out:
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strbuf_release(&gpg_status);
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strbuf_release(&gpg_output);
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return !!status;
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}
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void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
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{
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const char *output = flags & GPG_VERIFY_RAW ?
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sigc->gpg_status : sigc->gpg_output;
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if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
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fputs(sigc->payload, stdout);
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if (output)
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fputs(output, stderr);
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}
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size_t parse_signature(const char *buf, size_t size)
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{
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size_t len = 0;
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size_t match = size;
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while (len < size) {
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const char *eol;
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if (get_format_by_sig(buf + len))
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match = len;
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eol = memchr(buf + len, '\n', size - len);
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len += eol ? eol - (buf + len) + 1 : size - len;
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}
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return match;
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}
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void set_signing_key(const char *key)
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{
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free(configured_signing_key);
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configured_signing_key = xstrdup(key);
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}
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int git_gpg_config(const char *var, const char *value, void *cb)
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{
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struct gpg_format *fmt = NULL;
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char *fmtname = NULL;
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char *trust;
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int ret;
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if (!strcmp(var, "user.signingkey")) {
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if (!value)
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return config_error_nonbool(var);
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set_signing_key(value);
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return 0;
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}
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if (!strcmp(var, "gpg.format")) {
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if (!value)
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return config_error_nonbool(var);
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fmt = get_format_by_name(value);
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if (!fmt)
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return error("unsupported value for %s: %s",
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var, value);
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use_format = fmt;
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return 0;
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}
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if (!strcmp(var, "gpg.mintrustlevel")) {
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if (!value)
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return config_error_nonbool(var);
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trust = xstrdup_toupper(value);
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ret = parse_gpg_trust_level(trust, &configured_min_trust_level);
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free(trust);
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if (ret)
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return error("unsupported value for %s: %s", var,
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value);
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return 0;
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}
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if (!strcmp(var, "gpg.program") || !strcmp(var, "gpg.openpgp.program"))
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fmtname = "openpgp";
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if (!strcmp(var, "gpg.x509.program"))
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fmtname = "x509";
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if (fmtname) {
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fmt = get_format_by_name(fmtname);
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return git_config_string(&fmt->program, var, value);
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}
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return 0;
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}
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const char *get_signing_key(void)
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{
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if (configured_signing_key)
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return configured_signing_key;
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return git_committer_info(IDENT_STRICT|IDENT_NO_DATE);
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}
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int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
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{
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struct child_process gpg = CHILD_PROCESS_INIT;
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int ret;
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size_t i, j, bottom;
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struct strbuf gpg_status = STRBUF_INIT;
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argv_array_pushl(&gpg.args,
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use_format->program,
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"--status-fd=2",
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"-bsau", signing_key,
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NULL);
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bottom = signature->len;
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/*
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* When the username signingkey is bad, program could be terminated
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* because gpg exits without reading and then write gets SIGPIPE.
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*/
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sigchain_push(SIGPIPE, SIG_IGN);
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ret = pipe_command(&gpg, buffer->buf, buffer->len,
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signature, 1024, &gpg_status, 0);
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sigchain_pop(SIGPIPE);
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ret |= !strstr(gpg_status.buf, "\n[GNUPG:] SIG_CREATED ");
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strbuf_release(&gpg_status);
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if (ret)
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return error(_("gpg failed to sign the data"));
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/* Strip CR from the line endings, in case we are on Windows. */
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for (i = j = bottom; i < signature->len; i++)
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if (signature->buf[i] != '\r') {
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if (i != j)
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signature->buf[j] = signature->buf[i];
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j++;
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}
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strbuf_setlen(signature, j);
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return 0;
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}
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