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![Michał Górny](/assets/img/avatar_default.png)
GnuPG supports creating signatures consisting of multiple signature packets. If such a signature is verified, it outputs all the status messages for each signature separately. However, git currently does not account for such scenario and gets terribly confused over getting multiple *SIG statuses. For example, if a malicious party alters a signed commit and appends a new untrusted signature, git is going to ignore the original bad signature and report untrusted commit instead. However, %GK and %GS format strings may still expand to the data corresponding to the original signature, potentially tricking the scripts into trusting the malicious commit. Given that the use of multiple signatures is quite rare, git does not support creating them without jumping through a few hoops, and finally supporting them properly would require extensive API improvement, it seems reasonable to just reject them at the moment. Signed-off-by: Michał Górny <mgorny@gentoo.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
346 lines
8.4 KiB
C
346 lines
8.4 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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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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}
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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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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_EXCLUSIVE },
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{ 'B', "BADSIG ", GPG_STATUS_EXCLUSIVE },
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{ 'U', "TRUST_NEVER", 0 },
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{ 'U', "TRUST_UNDEFINED", 0 },
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{ 'E', "ERRSIG ", GPG_STATUS_EXCLUSIVE },
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{ 'X', "EXPSIG ", GPG_STATUS_EXCLUSIVE },
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{ 'Y', "EXPKEYSIG ", GPG_STATUS_EXCLUSIVE },
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{ 'R', "REVKEYSIG ", GPG_STATUS_EXCLUSIVE },
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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;
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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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/* 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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if (sigcheck_gpg_status[i].flags & GPG_STATUS_EXCLUSIVE) {
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if (++seen_exclusive_status > 1)
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goto found_duplicate_status;
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}
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sigc->result = sigcheck_gpg_status[i].result;
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/* The trust messages are not followed by key/signer information */
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if (sigc->result != 'U') {
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next = strchrnul(line, ' ');
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free(sigc->key);
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sigc->key = xmemdupz(line, next - line);
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/* The ERRSIG message is not followed by signer information */
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if (*next && sigc->result != 'E') {
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line = next + 1;
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next = strchrnul(line, '\n');
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free(sigc->signer);
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sigc->signer = xmemdupz(line, next - line);
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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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found_duplicate_status:
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/*
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* GOODSIG, BADSIG etc. can occur only once for each signature.
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* Therefore, if we had more than one then we're dealing with multiple
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* signatures. We don't support them currently, and they're rather
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* hard to create, so something is likely fishy and we should reject
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* them altogether.
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*/
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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->signer);
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FREE_AND_NULL(sigc->key);
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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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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' && sigc->result != 'U';
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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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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.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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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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