In order to prevent a valid push certificate for pushing into an
repository from getting replayed to push to an unrelated one, send a
nonce string from the receive-pack process and have the signer
include it in the push certificate. The original nonce is exported
as GIT_PUSH_CERT_NONCE for the hooks to examine and match against
the value on the "nonce" header in the certificate to notice a
replay.
Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
---
Documentation/git-receive-pack.txt | 8 ++++++++
Documentation/technical/pack-protocol.txt | 6 ++++++
Documentation/technical/protocol-capabilities.txt | 7 ++++---
builtin/receive-pack.c | 21 +++++++++++++++++++--
send-pack.c | 19 +++++++++++++++----
t/t5534-push-signed.sh | 17 +++++++++++------
6 files changed, 63 insertions(+), 15 deletions(-)
diff --git a/Documentation/git-receive-pack.txt b/Documentation/git-receive-pack.txt
index 60151a6..983b24e 100644
--- a/Documentation/git-receive-pack.txt
+++ b/Documentation/git-receive-pack.txt
@@ -72,6 +72,13 @@ GIT_PUSH_CERT_STATUS::
using the same mnemonic as used in `%G?` format of `git log`
family of commands (see linkgit:git-log[1]).
+GIT_PUSH_CERT_NONCE::
+ The nonce string the process asked the signer to include
+ in the push certificate. If this does not match the value
+ recorded on the "nonce" header in the push certificate, it
+ may indicate that the certificate is a valid one that is
+ being replayed from a separate "git push" session.
+
This hook is called before any refname is updated and before any
fast-forward checks are performed.
@@ -147,6 +154,7 @@ service:
if test -n "${GIT_PUSH_CERT-}" && test ${GIT_PUSH_CERT_STATUS} = G
then
(
+ echo expected nonce is ${GIT_PUSH_NONCE}
git cat-file blob ${GIT_PUSH_CERT}
) | mail -s "push from $GIT_PUSH_CERT_SIGNER" push-log@mydomain
fi
diff --git a/Documentation/technical/pack-protocol.txt b/Documentation/technical/pack-protocol.txt
index 7b543dc..dda1206 100644
--- a/Documentation/technical/pack-protocol.txt
+++ b/Documentation/technical/pack-protocol.txt
@@ -485,6 +485,7 @@ references.
PKT-LINE("certificate version 0.1" LF)
PKT-LINE("pusher" SP ident LF)
PKT-LINE("pushee" SP url LF)
+ PKT-LINE("nonce" SP nonce LF)
PKT-LINE(LF)
*PKT-LINE(command LF)
*PKT-LINE(gpg-signature-lines LF)
@@ -533,6 +534,11 @@ Currently, the following header fields are defined:
authentication material) the user who ran `git push`
intended to push into.
+`nonce` nonce::
+ The 'nonce' string the receiving repository asked the
+ pushing user to include in the certificate, to prevent
+ replay attacks.
+
The GPG signature lines are a detached signature for the contents
recorded in the push certificate before the signature block begins.
The detached signature is used to certify that the commands were
diff --git a/Documentation/technical/protocol-capabilities.txt b/Documentation/technical/protocol-capabilities.txt
index a478cc4..0c92dee 100644
--- a/Documentation/technical/protocol-capabilities.txt
+++ b/Documentation/technical/protocol-capabilities.txt
@@ -251,10 +251,11 @@ If the upload-pack server advertises this capability, fetch-pack may
send "want" lines with SHA-1s that exist at the server but are not
advertised by upload-pack.
-push-cert
----------
+push-cert=<nonce>
+-----------------
The receive-pack server that advertises this capability is willing
-to accept a signed push certificate. A send-pack client MUST NOT
+to accept a signed push certificate, and asks the <nonce> to be
+included in the push certificate. A send-pack client MUST NOT
send a push-cert packet unless the receive-pack server advertises
this capability.
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 2d93c87..9abfc94 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -52,6 +52,7 @@ static int accept_push_cert = 1;
static struct strbuf push_cert = STRBUF_INIT;
static unsigned char push_cert_sha1[20];
static struct signature_check sigcheck;
+static const char *push_cert_nonce;
static enum deny_action parse_deny_action(const char *var, const char *value)
{
@@ -157,8 +158,8 @@ static void show_ref(const char *path, const unsigned char *sha1)
"report-status delete-refs side-band-64k quiet");
if (prefer_ofs_delta)
strbuf_addstr(&cap, " ofs-delta");
- if (accept_push_cert)
- strbuf_addstr(&cap, " push-cert");
+ if (accept_push_cert && push_cert_nonce)
+ strbuf_addf(&cap, " push-cert=%s", push_cert_nonce);
strbuf_addf(&cap, " agent=%s", git_user_agent_sanitized());
packet_write(1, "%s %s%c%s\n",
sha1_to_hex(sha1), path, 0, cap.buf);
@@ -313,6 +314,8 @@ static void prepare_push_cert_sha1(struct child_process *proc)
argv_array_pushf(&env, "GIT_PUSH_CERT_KEY=%s",
sigcheck.key ? sigcheck.key : "");
argv_array_pushf(&env, "GIT_PUSH_CERT_STATUS=%c", sigcheck.result);
+ if (push_cert_nonce)
+ argv_array_pushf(&env, "GIT_PUSH_CERT_NONCE=%s", push_cert_nonce);
proc->env = env.argv;
}
@@ -1245,6 +1248,17 @@ static int delete_only(struct command *commands)
return 1;
}
+static char *prepare_push_cert_nonce(const char *dir)
+{
+ struct strbuf buf = STRBUF_INIT;
+ unsigned char sha1[20];
+
+ strbuf_addf(&buf, "%s:%lu", dir, time(NULL));
+ hash_sha1_file(buf.buf, buf.len, "blob", sha1);
+ strbuf_release(&buf);
+ return xstrdup(sha1_to_hex(sha1));
+}
+
int cmd_receive_pack(int argc, const char **argv, const char *prefix)
{
int advertise_refs = 0;
@@ -1304,6 +1318,8 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
die("'%s' does not appear to be a git repository", dir);
git_config(receive_pack_config, NULL);
+ if (accept_push_cert && !push_cert_nonce)
+ push_cert_nonce = prepare_push_cert_nonce(dir);
if (0 <= transfer_unpack_limit)
unpack_limit = transfer_unpack_limit;
@@ -1348,5 +1364,6 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
packet_flush(1);
sha1_array_clear(&shallow);
sha1_array_clear(&ref);
+ free((void *)push_cert_nonce);
return 0;
}
diff --git a/send-pack.c b/send-pack.c
index 642ebc8..141a6b2 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -228,7 +228,8 @@ static const char *next_line(const char *line, size_t len)
static int generate_push_cert(struct strbuf *req_buf,
const struct ref *remote_refs,
struct send_pack_args *args,
- const char *cap_string)
+ const char *cap_string,
+ const char *push_cert_nonce)
{
const struct ref *ref;
char stamp[60];
@@ -245,6 +246,8 @@ static int generate_push_cert(struct strbuf *req_buf,
strbuf_addf(&cert, "pushee %s\n", anon_url);
free(anon_url);
}
+ if (push_cert_nonce[0])
+ strbuf_addf(&cert, "nonce %s\n", push_cert_nonce);
strbuf_addstr(&cert, "\n");
for (ref = remote_refs; ref; ref = ref->next) {
@@ -295,6 +298,8 @@ int send_pack(struct send_pack_args *args,
unsigned cmds_sent = 0;
int ret;
struct async demux;
+ const char *push_cert_nonce = NULL;
+
/* Does the other end support the reporting? */
if (server_supports("report-status"))
@@ -311,8 +316,14 @@ 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"))
- die(_("the receiving end does not support --signed push"));
+ if (args->push_cert) {
+ int len;
+
+ push_cert_nonce = server_feature_value("push-cert", &len);
+ if (!push_cert_nonce)
+ die(_("the receiving end does not support --signed push"));
+ push_cert_nonce = xmemdupz(push_cert_nonce, len);
+ }
if (!remote_refs) {
fprintf(stderr, "No refs in common and none specified; doing nothing.\n"
@@ -343,7 +354,7 @@ int send_pack(struct send_pack_args *args,
if (!args->dry_run && args->push_cert)
cmds_sent = generate_push_cert(&req_buf, remote_refs, args,
- cap_buf.buf);
+ cap_buf.buf, push_cert_nonce);
/*
* Clear the status for each ref and see if we need to send
diff --git a/t/t5534-push-signed.sh b/t/t5534-push-signed.sh
index 35fe704..66fdaf2 100755
--- a/t/t5534-push-signed.sh
+++ b/t/t5534-push-signed.sh
@@ -72,17 +72,22 @@ test_expect_success GPG 'signed push sends push certificate' '
SIGNER=${GIT_PUSH_CERT_SIGNER-nobody}
KEY=${GIT_PUSH_CERT_KEY-nokey}
STATUS=${GIT_PUSH_CERT_STATUS-nostatus}
+ NONCE=${GIT_PUSH_CERT_NONCE-nononce}
E_O_F
EOF
- cat >expect <<-\EOF &&
- SIGNER=C O Mitter <committer@xxxxxxxxxxx>
- KEY=13B6F51ECDDE430D
- STATUS=G
- EOF
-
git push --signed dst noop ff +noff &&
+
+ (
+ cat <<-\EOF &&
+ SIGNER=C O Mitter <committer@xxxxxxxxxxx>
+ KEY=13B6F51ECDDE430D
+ STATUS=G
+ EOF
+ sed -n -e "s/^nonce /NONCE=/p" -e "/^$/q" dst/push-cert
+ ) >expect &&
+
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_cmp expect dst/push-cert-status
--
2.1.0-399-g1364b4d
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