ssh signing: retrieve a default key from ssh-agent
If user.signingkey is not set and a ssh signature is requested we call gpg.ssh.defaultKeyCommand (typically "ssh-add -L") and use the first key we get Signed-off-by: Fabian Stelzer <fs@gigacodes.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Fabian Stelzer committed
Sep 10, 2021 at 20:07 UTC
fd9e226776d1874af36b6b02fb2002b917af42fa
3 files changed
+77
-3
Documentation/config/gpg.txt
+6
@@ -33,3 +33,9 @@ gpg.minTrustLevel::
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* `marginal`
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* `fully`
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* `ultimate`
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+
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+gpg.ssh.defaultKeyCommand:
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+ This command that will be run when user.signingkey is not set and a ssh
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+ signature is requested. On successful exit a valid ssh public key is
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+ expected in the first line of its output. To automatically use the first
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+ available key from your ssh-agent set this to "ssh-add -L".
Documentation/config/user.txt
+3
-1
@@ -40,4 +40,6 @@ user.signingKey::
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key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and
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corresponds to the private key used for signing. The private key
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needs to be available via ssh-agent. Alternatively it can be set to
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- a file containing a private key directly.
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+ a file containing a private key directly. If not set git will call
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+ gpg.ssh.defaultKeyCommand (e.g.: "ssh-add -L") and try to use the first
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+ key available.
gpg-interface.c
+68
-2
@@ -6,8 +6,10 @@
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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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+#include "alias.h"
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static char *configured_signing_key;
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+static const char *ssh_default_key_command;
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static enum signature_trust_level configured_min_trust_level = TRUST_UNDEFINED;
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struct gpg_format {
@@ -21,6 +23,7 @@ struct gpg_format {
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size_t signature_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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+ const char *(*get_default_key)(void);
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};
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static const char *openpgp_verify_args[] = {
@@ -56,6 +59,8 @@ static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
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static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
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const char *signing_key);
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+static const char *get_default_ssh_signing_key(void);
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+
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static struct gpg_format gpg_format[] = {
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{
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.name = "openpgp",
@@ -64,6 +69,7 @@ static struct gpg_format gpg_format[] = {
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.sigs = openpgp_sigs,
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.verify_signed_buffer = verify_gpg_signed_buffer,
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.sign_buffer = sign_buffer_gpg,
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+ .get_default_key = NULL,
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},
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{
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.name = "x509",
@@ -72,6 +78,7 @@ static struct gpg_format gpg_format[] = {
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.sigs = x509_sigs,
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.verify_signed_buffer = verify_gpg_signed_buffer,
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.sign_buffer = sign_buffer_gpg,
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+ .get_default_key = NULL,
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},
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{
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.name = "ssh",
@@ -79,7 +86,8 @@ static struct gpg_format gpg_format[] = {
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.verify_args = ssh_verify_args,
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.sigs = ssh_sigs,
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.verify_signed_buffer = NULL, /* TODO */
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- .sign_buffer = sign_buffer_ssh
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+ .sign_buffer = sign_buffer_ssh,
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+ .get_default_key = get_default_ssh_signing_key,
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},
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};
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@@ -453,6 +461,12 @@ int git_gpg_config(const char *var, const char *value, void *cb)
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return 0;
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}
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+ if (!strcmp(var, "gpg.ssh.defaultkeycommand")) {
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+ if (!value)
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+ return config_error_nonbool(var);
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+ return git_config_string(&ssh_default_key_command, var, value);
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+ }
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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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@@ -470,11 +484,63 @@ int git_gpg_config(const char *var, const char *value, void *cb)
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return 0;
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}
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+/* Returns the first public key from an ssh-agent to use for signing */
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+static const char *get_default_ssh_signing_key(void)
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+{
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+ struct child_process ssh_default_key = CHILD_PROCESS_INIT;
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+ int ret = -1;
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+ struct strbuf key_stdout = STRBUF_INIT, key_stderr = STRBUF_INIT;
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+ struct strbuf **keys;
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+ char *key_command = NULL;
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+ const char **argv;
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+ int n;
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+ char *default_key = NULL;
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+
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+ if (!ssh_default_key_command)
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+ die(_("either user.signingkey or gpg.ssh.defaultKeyCommand needs to be configured"));
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+
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+ key_command = xstrdup(ssh_default_key_command);
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+ n = split_cmdline(key_command, &argv);
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+
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+ if (n < 0)
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+ die("malformed build-time gpg.ssh.defaultKeyCommand: %s",
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+ split_cmdline_strerror(n));
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+
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+ strvec_pushv(&ssh_default_key.args, argv);
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+ ret = pipe_command(&ssh_default_key, NULL, 0, &key_stdout, 0,
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+ &key_stderr, 0);
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+
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+ if (!ret) {
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+ keys = strbuf_split_max(&key_stdout, '\n', 2);
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+ if (keys[0] && starts_with(keys[0]->buf, "ssh-")) {
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+ default_key = strbuf_detach(keys[0], NULL);
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+ } else {
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+ warning(_("gpg.ssh.defaultKeycommand succeeded but returned no keys: %s %s"),
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+ key_stderr.buf, key_stdout.buf);
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+ }
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+
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+ strbuf_list_free(keys);
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+ } else {
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+ warning(_("gpg.ssh.defaultKeyCommand failed: %s %s"),
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+ key_stderr.buf, key_stdout.buf);
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+ }
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+
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+ free(key_command);
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+ free(argv);
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+ strbuf_release(&key_stdout);
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+
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+ return default_key;
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+}
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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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+ if (use_format->get_default_key) {
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+ return use_format->get_default_key();
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+ }
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+
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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)