/src/git/gpg-interface.c

Source (jump to first uncovered line)
#define USE_THE_REPOSITORY_VARIABLE

#include "git-compat-util.h"
#include "commit.h"
#include "config.h"
#include "date.h"
#include "gettext.h"
#include "run-command.h"
#include "strbuf.h"
#include "dir.h"
#include "ident.h"
#include "gpg-interface.h"
#include "path.h"
#include "sigchain.h"
#include "tempfile.h"
#include "alias.h"

static int git_gpg_config(const char *, const char *,
        const struct config_context *, void *);

static void gpg_interface_lazy_init(void)
{
  static int done;

  if (done)
    return;
  done = 1;
  git_config(git_gpg_config, NULL);
}

static char *configured_signing_key;
static char *ssh_default_key_command;
static char *ssh_allowed_signers;
static char *ssh_revocation_file;
static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;

struct gpg_format {
  const char *name;
  const char *program;
  const char **verify_args;
  const char **sigs;
  int (*verify_signed_buffer)(struct signature_check *sigc,
            struct gpg_format *fmt,
            const char *signature,
            size_t signature_size);
  int (*sign_buffer)(struct strbuf *buffer, struct strbuf *signature,
         const char *signing_key);
  const char *(*get_default_key)(void);
  const char *(*get_key_id)(void);
};

static const char *openpgp_verify_args[] = {
  "--keyid-format=long",
  NULL
};
static const char *openpgp_sigs[] = {
  "-----BEGIN PGP SIGNATURE-----",
  "-----BEGIN PGP MESSAGE-----",
  NULL
};

static const char *x509_verify_args[] = {
  NULL
};
static const char *x509_sigs[] = {
  "-----BEGIN SIGNED MESSAGE-----",
  NULL
};

static const char *ssh_verify_args[] = { NULL };
static const char *ssh_sigs[] = {
  "-----BEGIN SSH SIGNATURE-----",
  NULL
};

static int verify_gpg_signed_buffer(struct signature_check *sigc,
            struct gpg_format *fmt,
            const char *signature,
            size_t signature_size);
static int verify_ssh_signed_buffer(struct signature_check *sigc,
            struct gpg_format *fmt,
            const char *signature,
            size_t signature_size);
static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
         const char *signing_key);
static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
         const char *signing_key);

static const char *get_default_ssh_signing_key(void);

static const char *get_ssh_key_id(void);

static struct gpg_format gpg_format[] = {
  {
    .name = "openpgp",
    .program = "gpg",
    .verify_args = openpgp_verify_args,
    .sigs = openpgp_sigs,
    .verify_signed_buffer = verify_gpg_signed_buffer,
    .sign_buffer = sign_buffer_gpg,
    .get_default_key = NULL,
    .get_key_id = NULL,
  },
  {
    .name = "x509",
    .program = "gpgsm",
    .verify_args = x509_verify_args,
    .sigs = x509_sigs,
    .verify_signed_buffer = verify_gpg_signed_buffer,
    .sign_buffer = sign_buffer_gpg,
    .get_default_key = NULL,
    .get_key_id = NULL,
  },
  {
    .name = "ssh",
    .program = "ssh-keygen",
    .verify_args = ssh_verify_args,
    .sigs = ssh_sigs,
    .verify_signed_buffer = verify_ssh_signed_buffer,
    .sign_buffer = sign_buffer_ssh,
    .get_default_key = get_default_ssh_signing_key,
    .get_key_id = get_ssh_key_id,
  },
};

static struct gpg_format *use_format = &gpg_format[0];

static struct gpg_format *get_format_by_name(const char *str)
{
  int i;

  for (i = 0; i < ARRAY_SIZE(gpg_format); i++)
    if (!strcmp(gpg_format[i].name, str))
      return gpg_format + i;
  return NULL;
}

static struct gpg_format *get_format_by_sig(const char *sig)
{
  int i, j;

  for (i = 0; i < ARRAY_SIZE(gpg_format); i++)
    for (j = 0; gpg_format[i].sigs[j]; j++)
      if (starts_with(sig, gpg_format[i].sigs[j]))
        return gpg_format + i;
  return NULL;
}

void signature_check_clear(struct signature_check *sigc)
{
  FREE_AND_NULL(sigc->payload);
  FREE_AND_NULL(sigc->output);
  FREE_AND_NULL(sigc->gpg_status);
  FREE_AND_NULL(sigc->signer);
  FREE_AND_NULL(sigc->key);
  FREE_AND_NULL(sigc->fingerprint);
  FREE_AND_NULL(sigc->primary_key_fingerprint);
}

/* An exclusive status -- only one of them can appear in output */
#define GPG_STATUS_EXCLUSIVE  (1<<0)
/* The status includes key identifier */
#define GPG_STATUS_KEYID  (1<<1)
/* The status includes user identifier */
#define GPG_STATUS_UID    (1<<2)
/* The status includes key fingerprints */
#define GPG_STATUS_FINGERPRINT  (1<<3)
/* The status includes trust level */
#define GPG_STATUS_TRUST_LEVEL  (1<<4)

/* Short-hand for standard exclusive *SIG status with keyid & UID */
#define GPG_STATUS_STDSIG (GPG_STATUS_EXCLUSIVE|GPG_STATUS_KEYID|GPG_STATUS_UID)

static struct {
  char result;
  const char *check;
  unsigned int flags;
} sigcheck_gpg_status[] = {
  { 'G', "GOODSIG ", GPG_STATUS_STDSIG },
  { 'B', "BADSIG ", GPG_STATUS_STDSIG },
  { 'E', "ERRSIG ", GPG_STATUS_EXCLUSIVE|GPG_STATUS_KEYID },
  { 'X', "EXPSIG ", GPG_STATUS_STDSIG },
  { 'Y', "EXPKEYSIG ", GPG_STATUS_STDSIG },
  { 'R', "REVKEYSIG ", GPG_STATUS_STDSIG },
  { 0, "VALIDSIG ", GPG_STATUS_FINGERPRINT },
  { 0, "TRUST_", GPG_STATUS_TRUST_LEVEL },
};

/* Keep the order same as enum signature_trust_level */
static struct sigcheck_gpg_trust_level {
  const char *key;
  const char *display_key;
  enum signature_trust_level value;
} sigcheck_gpg_trust_level[] = {
  { "UNDEFINED", "undefined", TRUST_UNDEFINED },
  { "NEVER", "never", TRUST_NEVER },
  { "MARGINAL", "marginal", TRUST_MARGINAL },
  { "FULLY", "fully", TRUST_FULLY },
  { "ULTIMATE", "ultimate", TRUST_ULTIMATE },
};

static void replace_cstring(char **field, const char *line, const char *next)
{
  free(*field);

  if (line && next)
    *field = xmemdupz(line, next - line);
  else
    *field = NULL;
}

static int parse_gpg_trust_level(const char *level,
         enum signature_trust_level *res)
{
  size_t i;

  for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_trust_level); i++) {
    if (!strcmp(sigcheck_gpg_trust_level[i].key, level)) {
      *res = sigcheck_gpg_trust_level[i].value;
      return 0;
    }
  }
  return 1;
}

static void parse_gpg_output(struct signature_check *sigc)
{
  const char *buf = sigc->gpg_status;
  const char *line, *next;
  int i, j;
  int seen_exclusive_status = 0;

  /* Iterate over all lines */
  for (line = buf; *line; line = strchrnul(line+1, '\n')) {
    while (*line == '\n')
      line++;
    if (!*line)
      break;

    /* Skip lines that don't start with GNUPG status */
    if (!skip_prefix(line, "[GNUPG:] ", &line))
      continue;

    /* Iterate over all search strings */
    for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) {
      if (skip_prefix(line, sigcheck_gpg_status[i].check, &line)) {
        /*
         * GOODSIG, BADSIG etc. can occur only once for
         * each signature.  Therefore, if we had more
         * than one then we're dealing with multiple
         * signatures.  We don't support them
         * currently, and they're rather hard to
         * create, so something is likely fishy and we
         * should reject them altogether.
         */
        if (sigcheck_gpg_status[i].flags & GPG_STATUS_EXCLUSIVE) {
          if (seen_exclusive_status++)
            goto error;
        }

        if (sigcheck_gpg_status[i].result)
          sigc->result = sigcheck_gpg_status[i].result;
        /* Do we have key information? */
        if (sigcheck_gpg_status[i].flags & GPG_STATUS_KEYID) {
          next = strchrnul(line, ' ');
          replace_cstring(&sigc->key, line, next);
          /* Do we have signer information? */
          if (*next && (sigcheck_gpg_status[i].flags & GPG_STATUS_UID)) {
            line = next + 1;
            next = strchrnul(line, '\n');
            replace_cstring(&sigc->signer, line, next);
          }
        }

        /* Do we have trust level? */
        if (sigcheck_gpg_status[i].flags & GPG_STATUS_TRUST_LEVEL) {
          /*
           * GPG v1 and v2 differs in how the
           * TRUST_ lines are written.  Some
           * trust lines contain no additional
           * space-separated information for v1.
           */
          size_t trust_size = strcspn(line, " \n");
          char *trust = xmemdupz(line, trust_size);

          if (parse_gpg_trust_level(trust, &sigc->trust_level)) {
            free(trust);
            goto error;
          }
          free(trust);
        }

        /* Do we have fingerprint? */
        if (sigcheck_gpg_status[i].flags & GPG_STATUS_FINGERPRINT) {
          const char *limit;
          char **field;

          next = strchrnul(line, ' ');
          replace_cstring(&sigc->fingerprint, line, next);

          /*
           * Skip interim fields.  The search is
           * limited to the same line since only
           * OpenPGP signatures has a field with
           * the primary fingerprint.
           */
          limit = strchrnul(line, '\n');
          for (j = 9; j > 0; j--) {
            if (!*next || limit <= next)
              break;
            line = next + 1;
            next = strchrnul(line, ' ');
          }

          field = &sigc->primary_key_fingerprint;
          if (!j) {
            next = strchrnul(line, '\n');
            replace_cstring(field, line, next);
          } else {
            replace_cstring(field, NULL, NULL);
          }
        }

        break;
      }
    }
  }
  return;

error:
  sigc->result = 'E';
  /* Clear partial data to avoid confusion */
  FREE_AND_NULL(sigc->primary_key_fingerprint);
  FREE_AND_NULL(sigc->fingerprint);
  FREE_AND_NULL(sigc->signer);
  FREE_AND_NULL(sigc->key);
}

static int verify_gpg_signed_buffer(struct signature_check *sigc,
            struct gpg_format *fmt,
            const char *signature,
            size_t signature_size)
{
  struct child_process gpg = CHILD_PROCESS_INIT;
  struct tempfile *temp;
  int ret;
  struct strbuf gpg_stdout = STRBUF_INIT;
  struct strbuf gpg_stderr = STRBUF_INIT;

  temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
  if (!temp)
    return error_errno(_("could not create temporary file"));
  if (write_in_full(temp->fd, signature, signature_size) < 0 ||
      close_tempfile_gently(temp) < 0) {
    error_errno(_("failed writing detached signature to '%s'"),
          temp->filename.buf);
    delete_tempfile(&temp);
    return -1;
  }

  strvec_push(&gpg.args, fmt->program);
  strvec_pushv(&gpg.args, fmt->verify_args);
  strvec_pushl(&gpg.args,
         "--status-fd=1",
         "--verify", temp->filename.buf, "-",
         NULL);

  sigchain_push(SIGPIPE, SIG_IGN);
  ret = pipe_command(&gpg, sigc->payload, sigc->payload_len, &gpg_stdout, 0,
         &gpg_stderr, 0);
  sigchain_pop(SIGPIPE);

  delete_tempfile(&temp);

  ret |= !strstr(gpg_stdout.buf, "\n[GNUPG:] GOODSIG ");
  sigc->output = strbuf_detach(&gpg_stderr, NULL);
  sigc->gpg_status = strbuf_detach(&gpg_stdout, NULL);

  parse_gpg_output(sigc);

  strbuf_release(&gpg_stdout);
  strbuf_release(&gpg_stderr);

  return ret;
}

static void parse_ssh_output(struct signature_check *sigc)
{
  const char *line, *principal, *search;
  char *to_free;
  char *key = NULL;

  /*
   * ssh-keygen output should be:
   * Good "git" signature for PRINCIPAL with RSA key SHA256:FINGERPRINT
   *
   * or for valid but unknown keys:
   * Good "git" signature with RSA key SHA256:FINGERPRINT
   *
   * Note that "PRINCIPAL" can contain whitespace, "RSA" and
   * "SHA256" part could be a different token that names of
   * the algorithms used, and "FINGERPRINT" is a hexadecimal
   * string.  By finding the last occurence of " with ", we can
   * reliably parse out the PRINCIPAL.
   */
  sigc->result = 'B';
  sigc->trust_level = TRUST_NEVER;

  line = to_free = xmemdupz(sigc->output, strcspn(sigc->output, "\n"));

  if (skip_prefix(line, "Good \"git\" signature for ", &line)) {
    /* Search for the last "with" to get the full principal */
    principal = line;
    do {
      search = strstr(line, " with ");
      if (search)
        line = search + 1;
    } while (search != NULL);
    if (line == principal)
      goto cleanup;

    /* Valid signature and known principal */
    sigc->result = 'G';
    sigc->trust_level = TRUST_FULLY;
    sigc->signer = xmemdupz(principal, line - principal - 1);
  } else if (skip_prefix(line, "Good \"git\" signature with ", &line)) {
    /* Valid signature, but key unknown */
    sigc->result = 'G';
    sigc->trust_level = TRUST_UNDEFINED;
  } else {
    goto cleanup;
  }

  key = strstr(line, "key ");
  if (key) {
    sigc->fingerprint = xstrdup(strstr(line, "key ") + 4);
    sigc->key = xstrdup(sigc->fingerprint);
  } else {
    /*
     * Output did not match what we expected
     * Treat the signature as bad
     */
    sigc->result = 'B';
  }

cleanup:
  free(to_free);
}

static int verify_ssh_signed_buffer(struct signature_check *sigc,
            struct gpg_format *fmt,
            const char *signature,
            size_t signature_size)
{
  struct child_process ssh_keygen = CHILD_PROCESS_INIT;
  struct tempfile *buffer_file;
  int ret = -1;
  const char *line;
  char *principal;
  struct strbuf ssh_principals_out = STRBUF_INIT;
  struct strbuf ssh_principals_err = STRBUF_INIT;
  struct strbuf ssh_keygen_out = STRBUF_INIT;
  struct strbuf ssh_keygen_err = STRBUF_INIT;
  struct strbuf verify_time = STRBUF_INIT;
  const struct date_mode verify_date_mode = {
    .type = DATE_STRFTIME,
    .strftime_fmt = "%Y%m%d%H%M%S",
    /* SSH signing key validity has no timezone information - Use the local timezone */
    .local = 1,
  };

  if (!ssh_allowed_signers) {
    error(_("gpg.ssh.allowedSignersFile needs to be configured and exist for ssh signature verification"));
    return -1;
  }

  buffer_file = mks_tempfile_t(".git_vtag_tmpXXXXXX");
  if (!buffer_file)
    return error_errno(_("could not create temporary file"));
  if (write_in_full(buffer_file->fd, signature, signature_size) < 0 ||
      close_tempfile_gently(buffer_file) < 0) {
    error_errno(_("failed writing detached signature to '%s'"),
          buffer_file->filename.buf);
    delete_tempfile(&buffer_file);
    return -1;
  }

  if (sigc->payload_timestamp)
    strbuf_addf(&verify_time, "-Overify-time=%s",
      show_date(sigc->payload_timestamp, 0, verify_date_mode));

  /* Find the principal from the signers */
  strvec_pushl(&ssh_keygen.args, fmt->program,
         "-Y", "find-principals",
         "-f", ssh_allowed_signers,
         "-s", buffer_file->filename.buf,
         verify_time.buf,
         NULL);
  ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_principals_out, 0,
         &ssh_principals_err, 0);
  if (ret && strstr(ssh_principals_err.buf, "usage:")) {
    error(_("ssh-keygen -Y find-principals/verify is needed for ssh signature verification (available in openssh version 8.2p1+)"));
    goto out;
  }
  if (ret || !ssh_principals_out.len) {
    /*
     * We did not find a matching principal in the allowedSigners
     * Check without validation
     */
    child_process_init(&ssh_keygen);
    strvec_pushl(&ssh_keygen.args, fmt->program,
           "-Y", "check-novalidate",
           "-n", "git",
           "-s", buffer_file->filename.buf,
           verify_time.buf,
           NULL);
    pipe_command(&ssh_keygen, sigc->payload, sigc->payload_len,
           &ssh_keygen_out, 0, &ssh_keygen_err, 0);

    /*
     * Fail on unknown keys
     * we still call check-novalidate to display the signature info
     */
    ret = -1;
  } else {
    /* Check every principal we found (one per line) */
    const char *next;
    for (line = ssh_principals_out.buf;
         *line;
         line = next) {
      const char *end_of_text;

      next = end_of_text = strchrnul(line, '\n');

       /* Did we find a LF, and did we have CR before it? */
      if (*end_of_text &&
          line < end_of_text &&
          end_of_text[-1] == '\r')
        end_of_text--;

      /* Unless we hit NUL, skip over the LF we found */
      if (*next)
        next++;

      /* Not all lines are data.  Skip empty ones */
      if (line == end_of_text)
        continue;

      /* We now know we have an non-empty line. Process it */
      principal = xmemdupz(line, end_of_text - line);

      child_process_init(&ssh_keygen);
      strbuf_release(&ssh_keygen_out);
      strbuf_release(&ssh_keygen_err);
      strvec_push(&ssh_keygen.args, fmt->program);
      /*
       * We found principals
       * Try with each until we find a match
       */
      strvec_pushl(&ssh_keygen.args, "-Y", "verify",
             "-n", "git",
             "-f", ssh_allowed_signers,
             "-I", principal,
             "-s", buffer_file->filename.buf,
             verify_time.buf,
             NULL);

      if (ssh_revocation_file) {
        if (file_exists(ssh_revocation_file)) {
          strvec_pushl(&ssh_keygen.args, "-r",
                 ssh_revocation_file, NULL);
        } else {
          warning(_("ssh signing revocation file configured but not found: %s"),
            ssh_revocation_file);
        }
      }

      sigchain_push(SIGPIPE, SIG_IGN);
      ret = pipe_command(&ssh_keygen, sigc->payload, sigc->payload_len,
             &ssh_keygen_out, 0, &ssh_keygen_err, 0);
      sigchain_pop(SIGPIPE);

      FREE_AND_NULL(principal);

      if (!ret)
        ret = !starts_with(ssh_keygen_out.buf, "Good");

      if (!ret)
        break;
    }
  }

  strbuf_stripspace(&ssh_keygen_out, NULL);
  strbuf_stripspace(&ssh_keygen_err, NULL);
  /* Add stderr outputs to show the user actual ssh-keygen errors */
  strbuf_add(&ssh_keygen_out, ssh_principals_err.buf, ssh_principals_err.len);
  strbuf_add(&ssh_keygen_out, ssh_keygen_err.buf, ssh_keygen_err.len);
  sigc->output = strbuf_detach(&ssh_keygen_out, NULL);
  sigc->gpg_status = xstrdup(sigc->output);

  parse_ssh_output(sigc);

out:
  if (buffer_file)
    delete_tempfile(&buffer_file);
  strbuf_release(&ssh_principals_out);
  strbuf_release(&ssh_principals_err);
  strbuf_release(&ssh_keygen_out);
  strbuf_release(&ssh_keygen_err);
  strbuf_release(&verify_time);

  return ret;
}

static int parse_payload_metadata(struct signature_check *sigc)
{
  const char *ident_line = NULL;
  size_t ident_len;
  struct ident_split ident;
  const char *signer_header;

  switch (sigc->payload_type) {
  case SIGNATURE_PAYLOAD_COMMIT:
    signer_header = "committer";
    break;
  case SIGNATURE_PAYLOAD_TAG:
    signer_header = "tagger";
    break;
  case SIGNATURE_PAYLOAD_UNDEFINED:
  case SIGNATURE_PAYLOAD_PUSH_CERT:
    /* Ignore payloads we don't want to parse */
    return 0;
  default:
    BUG("invalid value for sigc->payload_type");
  }

  ident_line = find_commit_header(sigc->payload, signer_header, &ident_len);
  if (!ident_line || !ident_len)
    return 1;

  if (split_ident_line(&ident, ident_line, ident_len))
    return 1;

  if (!sigc->payload_timestamp && ident.date_begin && ident.date_end)
    sigc->payload_timestamp = parse_timestamp(ident.date_begin, NULL, 10);

  return 0;
}

int check_signature(struct signature_check *sigc,
        const char *signature, size_t slen)
{
  struct gpg_format *fmt;
  int status;

  gpg_interface_lazy_init();

  sigc->result = 'N';
  sigc->trust_level = TRUST_UNDEFINED;

  fmt = get_format_by_sig(signature);
  if (!fmt)
    die(_("bad/incompatible signature '%s'"), signature);

  if (parse_payload_metadata(sigc))
    return 1;

  status = fmt->verify_signed_buffer(sigc, fmt, signature, slen);

  if (status && !sigc->output)
    return !!status;

  status |= sigc->result != 'G';
  status |= sigc->trust_level < configured_min_trust_level;

  return !!status;
}

void print_signature_buffer(const struct signature_check *sigc, unsigned flags)
{
  const char *output = flags & GPG_VERIFY_RAW ? sigc->gpg_status :
                  sigc->output;

  if (flags & GPG_VERIFY_VERBOSE && sigc->payload)
    fwrite(sigc->payload, 1, sigc->payload_len, stdout);

  if (output)
    fputs(output, stderr);
}

size_t parse_signed_buffer(const char *buf, size_t size)
{
  size_t len = 0;
  size_t match = size;
  while (len < size) {
    const char *eol;

    if (get_format_by_sig(buf + len))
      match = len;

    eol = memchr(buf + len, '\n', size - len);
    len += eol ? eol - (buf + len) + 1 : size - len;
  }
  return match;
}

int parse_signature(const char *buf, size_t size, struct strbuf *payload, struct strbuf *signature)
{
  size_t match = parse_signed_buffer(buf, size);
  if (match != size) {
    strbuf_add(payload, buf, match);
    remove_signature(payload);
    strbuf_add(signature, buf + match, size - match);
    return 1;
  }
  return 0;
}

void set_signing_key(const char *key)
{
  gpg_interface_lazy_init();

  free(configured_signing_key);
  configured_signing_key = xstrdup(key);
}

static int git_gpg_config(const char *var, const char *value,
        const struct config_context *ctx UNUSED,
        void *cb UNUSED)
{
  struct gpg_format *fmt = NULL;
  const char *fmtname = NULL;
  char *trust;
  int ret;

  if (!strcmp(var, "user.signingkey")) {
    if (!value)
      return config_error_nonbool(var);
    set_signing_key(value);
    return 0;
  }

  if (!strcmp(var, "gpg.format")) {
    if (!value)
      return config_error_nonbool(var);
    fmt = get_format_by_name(value);
    if (!fmt)
      return error(_("invalid value for '%s': '%s'"),
             var, value);
    use_format = fmt;
    return 0;
  }

  if (!strcmp(var, "gpg.mintrustlevel")) {
    if (!value)
      return config_error_nonbool(var);

    trust = xstrdup_toupper(value);
    ret = parse_gpg_trust_level(trust, &configured_min_trust_level);
    free(trust);

    if (ret)
      return error(_("invalid value for '%s': '%s'"),
             var, value);
    return 0;
  }

  if (!strcmp(var, "gpg.ssh.defaultkeycommand"))
    return git_config_string(&ssh_default_key_command, var, value);

  if (!strcmp(var, "gpg.ssh.allowedsignersfile"))
    return git_config_pathname(&ssh_allowed_signers, var, value);

  if (!strcmp(var, "gpg.ssh.revocationfile"))
    return git_config_pathname(&ssh_revocation_file, var, value);

  if (!strcmp(var, "gpg.program") || !strcmp(var, "gpg.openpgp.program"))
    fmtname = "openpgp";

  if (!strcmp(var, "gpg.x509.program"))
    fmtname = "x509";

  if (!strcmp(var, "gpg.ssh.program"))
    fmtname = "ssh";

  if (fmtname) {
    fmt = get_format_by_name(fmtname);
    return git_config_string((char **) &fmt->program, var, value);
  }

  return 0;
}

/*
 * Returns 1 if `string` contains a literal ssh key, 0 otherwise
 * `key` will be set to the start of the actual key if a prefix is present.
 */
static int is_literal_ssh_key(const char *string, const char **key)
{
  if (skip_prefix(string, "key::", key))
    return 1;
  if (starts_with(string, "ssh-")) {
    *key = string;
    return 1;
  }
  return 0;
}

static char *get_ssh_key_fingerprint(const char *signing_key)
{
  struct child_process ssh_keygen = CHILD_PROCESS_INIT;
  int ret = -1;
  struct strbuf fingerprint_stdout = STRBUF_INIT;
  struct strbuf **fingerprint;
  char *fingerprint_ret;
  const char *literal_key = NULL;

  /*
   * With SSH Signing this can contain a filename or a public key
   * For textual representation we usually want a fingerprint
   */
  if (is_literal_ssh_key(signing_key, &literal_key)) {
    strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf", "-", NULL);
    ret = pipe_command(&ssh_keygen, literal_key,
           strlen(literal_key), &fingerprint_stdout, 0,
           NULL, 0);
  } else {
    strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf",
           configured_signing_key, NULL);
    ret = pipe_command(&ssh_keygen, NULL, 0, &fingerprint_stdout, 0,
           NULL, 0);
  }

  if (!!ret)
    die_errno(_("failed to get the ssh fingerprint for key '%s'"),
        signing_key);

  fingerprint = strbuf_split_max(&fingerprint_stdout, ' ', 3);
  if (!fingerprint[1])
    die_errno(_("failed to get the ssh fingerprint for key '%s'"),
        signing_key);

  fingerprint_ret = strbuf_detach(fingerprint[1], NULL);
  strbuf_list_free(fingerprint);
  strbuf_release(&fingerprint_stdout);
  return fingerprint_ret;
}

/* Returns the first public key from an ssh-agent to use for signing */
static const char *get_default_ssh_signing_key(void)
{
  struct child_process ssh_default_key = CHILD_PROCESS_INIT;
  int ret = -1;
  struct strbuf key_stdout = STRBUF_INIT, key_stderr = STRBUF_INIT;
  struct strbuf **keys;
  char *key_command = NULL;
  const char **argv;
  int n;
  char *default_key = NULL;
  const char *literal_key = NULL;

  if (!ssh_default_key_command)
    die(_("either user.signingkey or gpg.ssh.defaultKeyCommand needs to be configured"));

  key_command = xstrdup(ssh_default_key_command);
  n = split_cmdline(key_command, &argv);

  if (n < 0)
    die("malformed build-time gpg.ssh.defaultKeyCommand: %s",
        split_cmdline_strerror(n));

  strvec_pushv(&ssh_default_key.args, argv);
  ret = pipe_command(&ssh_default_key, NULL, 0, &key_stdout, 0,
         &key_stderr, 0);

  if (!ret) {
    keys = strbuf_split_max(&key_stdout, '\n', 2);
    if (keys[0] && is_literal_ssh_key(keys[0]->buf, &literal_key)) {
      /*
       * We only use `is_literal_ssh_key` here to check validity
       * The prefix will be stripped when the key is used.
       */
      default_key = strbuf_detach(keys[0], NULL);
    } else {
      warning(_("gpg.ssh.defaultKeyCommand succeeded but returned no keys: %s %s"),
        key_stderr.buf, key_stdout.buf);
    }

    strbuf_list_free(keys);
  } else {
    warning(_("gpg.ssh.defaultKeyCommand failed: %s %s"),
      key_stderr.buf, key_stdout.buf);
  }

  free(key_command);
  free(argv);
  strbuf_release(&key_stdout);

  return default_key;
}

static const char *get_ssh_key_id(void) {
  return get_ssh_key_fingerprint(get_signing_key());
}

/* Returns a textual but unique representation of the signing key */
const char *get_signing_key_id(void)
{
  gpg_interface_lazy_init();

  if (use_format->get_key_id) {
    return use_format->get_key_id();
  }

  /* GPG/GPGSM only store a key id on this variable */
  return get_signing_key();
}

const char *get_signing_key(void)
{
  gpg_interface_lazy_init();

  if (configured_signing_key)
    return configured_signing_key;
  if (use_format->get_default_key) {
    return use_format->get_default_key();
  }

  return git_committer_info(IDENT_STRICT | IDENT_NO_DATE);
}

const char *gpg_trust_level_to_str(enum signature_trust_level level)
{
  struct sigcheck_gpg_trust_level *trust;

  if (level < 0 || level >= ARRAY_SIZE(sigcheck_gpg_trust_level))
    BUG("invalid trust level requested %d", level);

  trust = &sigcheck_gpg_trust_level[level];
  if (trust->value != level)
    BUG("sigcheck_gpg_trust_level[] unsorted");

  return sigcheck_gpg_trust_level[level].display_key;
}

int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
{
  gpg_interface_lazy_init();

  return use_format->sign_buffer(buffer, signature, signing_key);
}

/*
 * Strip CR from the line endings, in case we are on Windows.
 * NEEDSWORK: make it trim only CRs before LFs and rename
 */
static void remove_cr_after(struct strbuf *buffer, size_t offset)
{
  size_t i, j;

  for (i = j = offset; i < buffer->len; i++) {
    if (buffer->buf[i] != '\r') {
      if (i != j)
        buffer->buf[j] = buffer->buf[i];
      j++;
    }
  }
  strbuf_setlen(buffer, j);
}

static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
        const char *signing_key)
{
  struct child_process gpg = CHILD_PROCESS_INIT;
  int ret;
  size_t bottom;
  const char *cp;
  struct strbuf gpg_status = STRBUF_INIT;

  strvec_pushl(&gpg.args,
         use_format->program,
         "--status-fd=2",
         "-bsau", signing_key,
         NULL);

  bottom = signature->len;

  /*
   * When the username signingkey is bad, program could be terminated
   * because gpg exits without reading and then write gets SIGPIPE.
   */
  sigchain_push(SIGPIPE, SIG_IGN);
  ret = pipe_command(&gpg, buffer->buf, buffer->len,
         signature, 1024, &gpg_status, 0);
  sigchain_pop(SIGPIPE);

  for (cp = gpg_status.buf;
       cp && (cp = strstr(cp, "[GNUPG:] SIG_CREATED "));
       cp++) {
    if (cp == gpg_status.buf || cp[-1] == '\n')
      break; /* found */
  }
  ret |= !cp;
  if (ret) {
    error(_("gpg failed to sign the data:\n%s"),
          gpg_status.len ? gpg_status.buf : "(no gpg output)");
    strbuf_release(&gpg_status);
    return -1;
  }
  strbuf_release(&gpg_status);

  /* Strip CR from the line endings, in case we are on Windows. */
  remove_cr_after(signature, bottom);

  return 0;
}

static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
         const char *signing_key)
{
  struct child_process signer = CHILD_PROCESS_INIT;
  int ret = -1;
  size_t bottom, keylen;
  struct strbuf signer_stderr = STRBUF_INIT;
  struct tempfile *key_file = NULL, *buffer_file = NULL;
  char *ssh_signing_key_file = NULL;
  struct strbuf ssh_signature_filename = STRBUF_INIT;
  const char *literal_key = NULL;
  int literal_ssh_key = 0;

  if (!signing_key || signing_key[0] == '\0')
    return error(
      _("user.signingKey needs to be set for ssh signing"));

  if (is_literal_ssh_key(signing_key, &literal_key)) {
    /* A literal ssh key */
    literal_ssh_key = 1;
    key_file = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
    if (!key_file)
      return error_errno(
        _("could not create temporary file"));
    keylen = strlen(literal_key);
    if (write_in_full(key_file->fd, literal_key, keylen) < 0 ||
        close_tempfile_gently(key_file) < 0) {
      error_errno(_("failed writing ssh signing key to '%s'"),
            key_file->filename.buf);
      goto out;
    }
    ssh_signing_key_file = strbuf_detach(&key_file->filename, NULL);
  } else {
    /* We assume a file */
    ssh_signing_key_file = interpolate_path(signing_key, 1);
  }

  buffer_file = mks_tempfile_t(".git_signing_buffer_tmpXXXXXX");
  if (!buffer_file) {
    error_errno(_("could not create temporary file"));
    goto out;
  }

  if (write_in_full(buffer_file->fd, buffer->buf, buffer->len) < 0 ||
      close_tempfile_gently(buffer_file) < 0) {
    error_errno(_("failed writing ssh signing key buffer to '%s'"),
          buffer_file->filename.buf);
    goto out;
  }

  strvec_pushl(&signer.args, use_format->program,
         "-Y", "sign",
         "-n", "git",
         "-f", ssh_signing_key_file,
         NULL);
  if (literal_ssh_key)
    strvec_push(&signer.args, "-U");
  strvec_push(&signer.args, buffer_file->filename.buf);

  sigchain_push(SIGPIPE, SIG_IGN);
  ret = pipe_command(&signer, NULL, 0, NULL, 0, &signer_stderr, 0);
  sigchain_pop(SIGPIPE);

  if (ret) {
    if (strstr(signer_stderr.buf, "usage:"))
      error(_("ssh-keygen -Y sign is needed for ssh signing (available in openssh version 8.2p1+)"));

    ret = error("%s", signer_stderr.buf);
    goto out;
  }

  bottom = signature->len;

  strbuf_addbuf(&ssh_signature_filename, &buffer_file->filename);
  strbuf_addstr(&ssh_signature_filename, ".sig");
  if (strbuf_read_file(signature, ssh_signature_filename.buf, 0) < 0) {
    ret = error_errno(
      _("failed reading ssh signing data buffer from '%s'"),
      ssh_signature_filename.buf);
    goto out;
  }
  /* Strip CR from the line endings, in case we are on Windows. */
  remove_cr_after(signature, bottom);

out:
  if (key_file)
    delete_tempfile(&key_file);
  if (buffer_file)
    delete_tempfile(&buffer_file);
  if (ssh_signature_filename.len)
    unlink_or_warn(ssh_signature_filename.buf);
  strbuf_release(&signer_stderr);
  strbuf_release(&ssh_signature_filename);
  FREE_AND_NULL(ssh_signing_key_file);
  return ret;
}

Coverage Report

Created: 2024-09-08 06:24