While signed tags and commits assert that the objects thusly signed came from you, who signed these objects, there is not a good way to assert that you wanted to have a particular object at the tip of a particular branch. My signing v2.0.1 tag only means I want to call the version v2.0.1, and it does not mean I want to push it out to my 'master' branch---it is likely that I only want it in 'maint'.
Introduce a mechanism that allows you to sign a "push certificate" (for the lack of better name) every time you push, asserting that what object you are pushing to update which ref that used to point at what other object. Think of it as a cryptographic protection for ref updates, similar to signed tags/commits but working on an orthogonal axis.
The basic flow based on this mechanism goes like this:
1. You push out your work with "git push -s".
2. The sending side learns where the remote refs are as usual,
together with what protocol extension the receiving end
supports. If the receiving end does not advertise the protocol
extension "push-cert", the sending side falls back to the normal
push that is not signed. Otherwise, a text file, that looks like the following, is
prepared in core: certificate version 0.1
pusher Junio C Hamano <gitster@pobox.com> 1315427886 -0700
7339ca65... 21580ecb... refs/heads/master
3793ac56... 12850bec... refs/heads/next
Each line shows the old and the new object name at the tip of
the ref this push tries to update, in the way identical to how
the underlying "git push" protocol exchange tells the ref
updates to the receiving end (by recording the "old" object
name, the push certificate also protects against replaying). It
is expected that new command packet types other than the
old-new-refname kind will be included in push certificate in the
same way as would appear in the plain vanilla command packets in
unsigned pushes. The user then is asked to sign this push certificate using GPG,
formatted in a way similar to how signed tag objects are signed,
and the result is sent to the other side (i.e. receive-pack). In the protocol exchange, this step comes immediately before the
sender tells what the result of the push should be, which in
turn comes before it sends the pack data. 3. When the receiving end sees a push certificate, the certificate
is written out as a blob. The pre-receive hook can learn about
the certificate by checking GIT_PUSH_CERT environment variable,
which, if present, tells the object name of this blob, and make
the decision to allow or reject this push. Additionally, the
post-receive hook can also look at the certificate, which may be
a good place to log all the received certificates for later
audits.Because a push certificate carry the same information as the usual command packets in the protocol exchange, we can omit the latter when a push certificate is in use and reduce the protocol overhead. This however is not included in this patch to make it easier to review (in other words, the series at this step should never be released without the remainder of the series, as it implements an interim protocol that will be incompatible with the final one, merely for reviewing purposes). As such, the documentation update for the protocol is left out of this step.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
Documentation/git-push.txt | 9 +++++-
Documentation/git-receive-pack.txt | 16 ++++++++-
builtin/push.c | 1 +
builtin/receive-pack.c | 43 ++++++++++++++++++++++++-
send-pack.c | 66 ++++++++++++++++++++++++++++++++++++++
send-pack.h | 1 +
t/t5534-push-signed.sh | 63 ++++++++++++++++++++++++++++++++++++
transport.c | 4 +++
transport.h | 5 +++
9 files changed, 205 insertions(+), 3 deletions(-)
create mode 100755 t/t5534-push-signed.sh
Show changes to 9 files +205 −3
Documentation/git-push.txt, Documentation/git-receive-pack.txt, builtin/push.c, builtin/receive-pack.c, send-pack.c, send-pack.h, t/t5534-push-signed.sh, transport.c, transport.h
diff --git a/Documentation/git-push.txt b/Documentation/git-push.txt
index 21cd455..21b3f29 100644
--- a/Documentation/git-push.txt
+++ b/Documentation/git-push.txt
@@ -10,7 +10,8 @@ SYNOPSIS
--------
[verse]
'git push' [--all | --mirror | --tags] [--follow-tags] [-n | --dry-run] [--receive-pack=<git-receive-pack>]
- [--repo=<repository>] [-f | --force] [--prune] [-v | --verbose] [-u | --set-upstream]
+ [--repo=<repository>] [-f | --force] [--prune] [-v | --verbose]
+ [-u | --set-upstream] [--signed]
[--force-with-lease[=<refname>[:<expect>]]]
[--no-verify] [<repository> [<refspec>...]]
@@ -129,6 +130,12 @@ already exists on the remote side.
from the remote but are pointing at commit-ish that are
reachable from the refs being pushed.
+--signed::
+ GPG-sign the push request to update refs on the receiving
+ side, to allow it to be checked by the hooks and/or be
+ logged. See linkgit:git-receive-pack[1] for the details
+ on the receiving end.
+
--receive-pack=<git-receive-pack>::
--exec=<git-receive-pack>::
Path to the 'git-receive-pack' program on the remote
diff --git a/Documentation/git-receive-pack.txt b/Documentation/git-receive-pack.txt
index b1f7dc6..6c458af 100644
--- a/Documentation/git-receive-pack.txt
+++ b/Documentation/git-receive-pack.txt
@@ -53,6 +53,11 @@ the update. Refs to be created will have sha1-old equal to 0\{40},
while refs to be deleted will have sha1-new equal to 0\{40}, otherwise
sha1-old and sha1-new should be valid objects in the repository.
+When accepting a signed push (see linkgit:git-push[1]), the signed
+push certificate is stored in a blob and an environment variable
+`GIT_PUSH_CERT` can be consulted for its object name. See the
+description of `post-receive` hook for an example.
+
This hook is called before any refname is updated and before any
fast-forward checks are performed.
@@ -101,9 +106,13 @@ the update. Refs that were created will have sha1-old equal to
0\{40}, otherwise sha1-old and sha1-new should be valid objects in
the repository.
+The `GIT_PUSH_CERT` environment variable can be inspected, just as
+in `pre-receive` hook, after accepting a signed push.
+
Using this hook, it is easy to generate mails describing the updates
to the repository. This example script sends one mail message per
-ref listing the commits pushed to the repository:
+ref listing the commits pushed to the repository, and logs the push
+certificates of signed pushes to a file:
#!/bin/sh
# mail out commit update information.
@@ -119,6 +128,11 @@ ref listing the commits pushed to the repository:
fi |
mail -s "Changes to ref $ref" commit-list@mydomain
done
+ # log signed push certificate, if any
+ if test -n "${GIT_PUSH_CERT-}"
+ then
+ git cat-file blob ${GIT_PUSH_CERT} >>/var/log/push-log
+ fi
exit 0
The exit code from this hook invocation is ignored, however a
diff --git a/builtin/push.c b/builtin/push.c
index f50e3d5..ae56f73 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -506,6 +506,7 @@ int cmd_push(int argc, const char **argv, const char *prefix)
OPT_BIT(0, "no-verify", &flags, N_("bypass pre-push hook"), TRANSPORT_PUSH_NO_HOOK),
OPT_BIT(0, "follow-tags", &flags, N_("push missing but relevant tags"),
TRANSPORT_PUSH_FOLLOW_TAGS),
+ OPT_BIT(0, "signed", &flags, N_("GPG sign the push"), TRANSPORT_PUSH_CERT),
OPT_END()
};
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 341bb46..f30df8a 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -46,6 +46,8 @@ static void *head_name_to_free;
static int sent_capabilities;
static int shallow_update;
static const char *alt_shallow_file;
+static struct strbuf push_cert = STRBUF_INIT;
+static unsigned char push_cert_sha1[20];
static enum deny_action parse_deny_action(const char *var, const char *value)
{
@@ -142,7 +144,7 @@ static void show_ref(const char *path, const unsigned char *sha1)
else
packet_write(1, "%s %s%c%s%s agent=%s\n",
sha1_to_hex(sha1), path, 0,
- " report-status delete-refs side-band-64k quiet",
+ " report-status delete-refs side-band-64k quiet push-cert",
prefer_ofs_delta ? " ofs-delta" : "",
git_user_agent_sanitized());
sent_capabilities = 1;
@@ -252,6 +254,22 @@ static int copy_to_sideband(int in, int out, void *arg)
return 0;
}
+static void prepare_push_cert_sha1(struct child_process *proc)
+{
+ static int already_done;
+ struct argv_array env = ARGV_ARRAY_INIT;
+
+ if (!already_done) {
+ already_done = 1;
+ if (write_sha1_file(push_cert.buf, push_cert.len, "blob", push_cert_sha1))
+ hashclr(push_cert_sha1);
+ }
+ if (!is_null_sha1(push_cert_sha1)) {
+ argv_array_pushf(&env, "GIT_PUSH_CERT=%s", sha1_to_hex(push_cert_sha1));
+ proc->env = env.argv;
+ }
+}
+
typedef int (*feed_fn)(void *, const char **, size_t *);
static int run_and_feed_hook(const char *hook_name, feed_fn feed, void *feed_state)
{
@@ -271,6 +289,8 @@ static int run_and_feed_hook(const char *hook_name, feed_fn feed, void *feed_sta
proc.in = -1;
proc.stdout_to_stderr = 1;
+ prepare_push_cert_sha1(&proc);
+
if (use_sideband) {
memset(&muxer, 0, sizeof(muxer));
muxer.proc = copy_to_sideband;
@@ -890,6 +910,27 @@ static struct command *read_head_info(struct sha1_array *shallow)
quiet = 1;
}
+ if (!strcmp(line, "push-cert")) {
+ int true_flush = 0;
+ char certbuf[1024];
+
+ for (;;) {
+ len = packet_read(0, NULL, NULL,
+ certbuf, sizeof(certbuf), 0);
+ if (!len) {
+ true_flush = 1;
+ break;
+ }
+ if (!strcmp(certbuf, "push-cert-end\n"))
+ break; /* end of cert */
+ strbuf_addstr(&push_cert, certbuf);
+ }
+
+ if (true_flush)
+ break;
+ continue;
+ }
+
p = queue_command(p, line, linelen);
}
return commands;
diff --git a/send-pack.c b/send-pack.c
index 05926d2..a073891 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -11,6 +11,7 @@
#include "transport.h"
#include "version.h"
#include "sha1-array.h"
+#include "gpg-interface.h"
static int feed_object(const unsigned char *sha1, int fd, int negative)
{
@@ -210,6 +211,64 @@ static int ref_update_to_be_sent(const struct ref *ref, const struct send_pack_a
}
}
+/*
+ * the beginning of the next line, or the end of buffer.
+ *
+ * NEEDSWORK: perhaps move this to git-compat-util.h or somewhere and
+ * convert many similar uses found by "git grep -A4 memchr".
+ */
+static const char *next_line(const char *line, size_t len)
+{
+ const char *nl = memchr(line, '\n', len);
+ if (!nl)
+ return line + len; /* incomplete line */
+ return nl + 1;
+}
+
+static void generate_push_cert(struct strbuf *req_buf,
+ const struct ref *remote_refs,
+ struct send_pack_args *args)
+{
+ const struct ref *ref;
+ char stamp[60];
+ char *signing_key = xstrdup(get_signing_key());
+ const char *cp, *np;
+ struct strbuf cert = STRBUF_INIT;
+ int update_seen = 0;
+
+ datestamp(stamp, sizeof(stamp));
+ strbuf_addf(&cert, "certificate version 0.1\n");
+ strbuf_addf(&cert, "pusher %s %s\n", signing_key, stamp);
+ strbuf_addstr(&cert, "\n");
+
+ for (ref = remote_refs; ref; ref = ref->next) {
+ if (!ref_update_to_be_sent(ref, args))
+ continue;
+ update_seen = 1;
+ strbuf_addf(&cert, "%s %s %s\n",
+ sha1_to_hex(ref->old_sha1),
+ sha1_to_hex(ref->new_sha1),
+ ref->name);
+ }
+ if (!update_seen)
+ goto free_return;
+
+ if (sign_buffer(&cert, &cert, signing_key))
+ die(_("failed to sign the push certificate"));
+
+ packet_buf_write(req_buf, "push-cert\n");
+ for (cp = cert.buf; cp < cert.buf + cert.len; cp = np) {
+ np = next_line(cp, cert.buf + cert.len - cp);
+ packet_buf_write(req_buf,
+ "%.*s", (int)(np - cp), cp);
+ }
+ packet_buf_write(req_buf, "push-cert-end\n");
+
+free_return:
+ free(signing_key);
+ strbuf_release(&cert);
+}
+
int send_pack(struct send_pack_args *args,
int fd[], struct child_process *conn,
struct ref *remote_refs,
@@ -245,6 +304,10 @@ int send_pack(struct send_pack_args *args,
agent_supported = 1;
if (server_supports("no-thin"))
args->use_thin_pack = 0;
+ if (args->push_cert && !server_supports("push-cert")) {
+ warning(_("the receiving end does not support --signed push"));
+ args->push_cert = 0;
+ }
if (!remote_refs) {
fprintf(stderr, "No refs in common and none specified; doing nothing.\n"
@@ -273,6 +336,9 @@ int send_pack(struct send_pack_args *args,
if (!args->dry_run)
advertise_shallow_grafts_buf(&req_buf);
+ if (!args->dry_run && args->push_cert)
+ generate_push_cert(&req_buf, remote_refs, args);
+
/*
* Clear the status for each ref and see if we need to send
* the pack data.
diff --git a/send-pack.h b/send-pack.h
index 8e84392..3555d8e 100644
--- a/send-pack.h
+++ b/send-pack.h
@@ -11,6 +11,7 @@ struct send_pack_args {
use_thin_pack:1,
use_ofs_delta:1,
dry_run:1,
+ push_cert:1,
stateless_rpc:1;
};
diff --git a/t/t5534-push-signed.sh b/t/t5534-push-signed.sh
new file mode 100755
index 0000000..0eb5004
--- /dev/null
+++ b/t/t5534-push-signed.sh
@@ -0,0 +1,63 @@
+#!/bin/sh
+
+test_description='signed push'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-gpg.sh
+
+prepare_dst () {
+ rm -fr dst &&
+ test_create_repo dst &&
+
+ git push dst master:noop master:ff master:noff
+}
+
+test_expect_success setup '
+ # master, ff and noff branches pointing at the same commit
+ test_tick &&
+ git commit --allow-empty -m initial &&
+
+ git checkout -b noop &&
+ git checkout -b ff &&
+ git checkout -b noff &&
+
+ # noop stays the same, ff advances, noff rewrites
+ test_tick &&
+ git commit --allow-empty --amend -m rewritten &&
+ git checkout ff &&
+
+ test_tick &&
+ git commit --allow-empty -m second
+'
+
+test_expect_success 'unsigned push does not send push certificate' '
+ prepare_dst &&
+ mkdir -p dst/.git/hooks &&
+ write_script dst/.git/hooks/post-receive <<-\EOF &&
+ if test -n "${GIT_PUSH_CERT-}"
+ then
+ git cat-file blob $GIT_PUSH_CERT >../push-cert
+ fi
+ EOF
+
+ git push dst noop ff +noff &&
+ test -f dst/push-cert &&
+ ! test -s dst/push-cert
+'
+
+test_expect_success GPG 'signed push sends push certificate' '
+ prepare_dst &&
+ mkdir -p dst/.git/hooks &&
+ write_script dst/.git/hooks/post-receive <<-\EOF &&
+ if test -n "${GIT_PUSH_CERT-}"
+ then
+ git cat-file blob $GIT_PUSH_CERT >../push-cert
+ fi
+ EOF
+
+ git push --signed dst noop ff +noff &&
+ grep "$(git rev-parse noop ff) refs/heads/ff" dst/push-cert &&
+ grep "$(git rev-parse noop noff) refs/heads/noff" dst/push-cert
+'
+
+test_done
diff --git a/transport.c b/transport.c
index 662421b..07fdf86 100644
--- a/transport.c
+++ b/transport.c
@@ -480,6 +480,9 @@ static int set_git_option(struct git_transport_options *opts,
die("transport: invalid depth option '%s'", value);
}
return 0;
+ } else if (!strcmp(name, TRANS_OPT_PUSH_CERT)) {
+ opts->push_cert = !!value;
+ return 0;
}
return 1;
}
@@ -823,6 +826,7 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
args.progress = transport->progress;
args.dry_run = !!(flags & TRANSPORT_PUSH_DRY_RUN);
args.porcelain = !!(flags & TRANSPORT_PUSH_PORCELAIN);
+ args.push_cert = !!(flags & TRANSPORT_PUSH_CERT);
ret = send_pack(&args, data->fd, data->conn, remote_refs,
&data->extra_have);
diff --git a/transport.h b/transport.h
index 02ea248..3e0091e 100644
--- a/transport.h
+++ b/transport.h
@@ -12,6 +12,7 @@ struct git_transport_options {
unsigned check_self_contained_and_connected : 1;
unsigned self_contained_and_connected : 1;
unsigned update_shallow : 1;
+ unsigned push_cert : 1;
int depth;
const char *uploadpack;
const char *receivepack;
@@ -123,6 +124,7 @@ struct transport {
#define TRANSPORT_RECURSE_SUBMODULES_ON_DEMAND 256
#define TRANSPORT_PUSH_NO_HOOK 512
#define TRANSPORT_PUSH_FOLLOW_TAGS 1024
+#define TRANSPORT_PUSH_CERT 2048
#define TRANSPORT_SUMMARY_WIDTH (2 * DEFAULT_ABBREV + 3)
#define TRANSPORT_SUMMARY(x) (int)(TRANSPORT_SUMMARY_WIDTH + strlen(x) - gettext_width(x)), (x)
@@ -156,6 +158,9 @@ struct transport *transport_get(struct remote *, const char *);
/* Accept refs that may update .git/shallow without --depth */
#define TRANS_OPT_UPDATE_SHALLOW "updateshallow"
+/* Send push certificates */
+#define TRANS_OPT_PUSH_CERT "pushcert"
+
/**
* Returns 0 if the option was used, non-zero otherwise. Prints a
* message to stderr if the option is not used.
Junio C Hamano
