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authorJunio C Hamano <gitster@pobox.com>2014-09-05 17:46:04 (GMT)
committerJunio C Hamano <gitster@pobox.com>2014-09-17 22:19:54 (GMT)
commit5732373daacf9486a0db9741cf0de4e7a41b08b3 (patch)
treece6e9a4c1262238e1a63f01817abb95b8e1c0984 /builtin/receive-pack.c
parent0ea47f9d3307bdb1cd9364acd3e4a463b244bba2 (diff)
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signed push: allow stale nonce in stateless mode
When operating with the stateless RPC mode, we will receive a nonce issued by another instance of us that advertised our capability and refs some time ago. Update the logic to check received nonce to detect this case, compute how much time has passed since the nonce was issued and report the status with a new environment variable GIT_PUSH_CERT_NONCE_SLOP to the hooks. GIT_PUSH_CERT_NONCE_STATUS will report "SLOP" in such a case. The hooks are free to decide how large a slop it is willing to accept. Strictly speaking, the "nonce" is not really a "nonce" anymore in the stateless RPC mode, as it will happily take any "nonce" issued by it (which is protected by HMAC and its secret key) as long as it is fresh enough. The degree of this security degradation, relative to the native protocol, is about the same as the "we make sure that the 'git push' decided to update our refs with new objects based on the freshest observation of our refs by making sure the values they claim the original value of the refs they ask us to update exactly match the current state" security is loosened to accomodate the stateless RPC mode in the existing code without this series, so there is no need for those who are already using smart HTTP to push to their repositories to be alarmed any more than they already are. In addition, the server operator can set receive.certnonceslop configuration variable to specify how stale a nonce can be (in seconds). When this variable is set, and if the nonce received in the certificate that passes the HMAC check was less than that many seconds old, hooks are given "OK" in GIT_PUSH_CERT_NONCE_STATUS (instead of "SLOP") and the received nonce value is given in GIT_PUSH_CERT_NONCE, which makes it easier for a simple-minded hook to check if the certificate we received is recent enough. Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'builtin/receive-pack.c')
-rw-r--r--builtin/receive-pack.c89
1 files changed, 79 insertions, 10 deletions
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 91d1a6f..efb13b1 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -43,6 +43,8 @@ static int prefer_ofs_delta = 1;
static int auto_update_server_info;
static int auto_gc = 1;
static int fix_thin = 1;
+static int stateless_rpc;
+static const char *service_dir;
static const char *head_name;
static void *head_name_to_free;
static int sent_capabilities;
@@ -58,7 +60,10 @@ static const char *NONCE_UNSOLICITED = "UNSOLICITED";
static const char *NONCE_BAD = "BAD";
static const char *NONCE_MISSING = "MISSING";
static const char *NONCE_OK = "OK";
+static const char *NONCE_SLOP = "SLOP";
static const char *nonce_status;
+static long nonce_stamp_slop;
+static unsigned long nonce_stamp_slop_limit;
static enum deny_action parse_deny_action(const char *var, const char *value)
{
@@ -145,6 +150,11 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
if (strcmp(var, "receive.certnonceseed") == 0)
return git_config_string(&cert_nonce_seed, var, value);
+ if (strcmp(var, "receive.certnonceslop") == 0) {
+ nonce_stamp_slop_limit = git_config_ulong(var, value);
+ return 0;
+ }
+
return git_default_config(var, value, cb);
}
@@ -359,6 +369,8 @@ static char *find_header(const char *msg, size_t len, const char *key)
static const char *check_nonce(const char *buf, size_t len)
{
char *nonce = find_header(buf, len, "nonce");
+ unsigned long stamp, ostamp;
+ char *bohmac, *expect = NULL;
const char *retval = NONCE_BAD;
if (!nonce) {
@@ -372,11 +384,67 @@ static const char *check_nonce(const char *buf, size_t len)
goto leave;
}
- /* returned nonce MUST match what we gave out earlier */
- retval = NONCE_BAD;
+ if (!stateless_rpc) {
+ /* returned nonce MUST match what we gave out earlier */
+ retval = NONCE_BAD;
+ goto leave;
+ }
+
+ /*
+ * In stateless mode, we may be receiving a nonce issued by
+ * another instance of the server that serving the same
+ * repository, and the timestamps may not match, but the
+ * nonce-seed and dir should match, so we can recompute and
+ * report the time slop.
+ *
+ * In addition, when a nonce issued by another instance has
+ * timestamp within receive.certnonceslop seconds, we pretend
+ * as if we issued that nonce when reporting to the hook.
+ */
+
+ /* nonce is concat(<seconds-since-epoch>, "-", <hmac>) */
+ if (*nonce <= '0' || '9' < *nonce) {
+ retval = NONCE_BAD;
+ goto leave;
+ }
+ stamp = strtoul(nonce, &bohmac, 10);
+ if (bohmac == nonce || bohmac[0] != '-') {
+ retval = NONCE_BAD;
+ goto leave;
+ }
+
+ expect = prepare_push_cert_nonce(service_dir, stamp);
+ if (strcmp(expect, nonce)) {
+ /* Not what we would have signed earlier */
+ retval = NONCE_BAD;
+ goto leave;
+ }
+
+ /*
+ * By how many seconds is this nonce stale? Negative value
+ * would mean it was issued by another server with its clock
+ * skewed in the future.
+ */
+ ostamp = strtoul(push_cert_nonce, NULL, 10);
+ nonce_stamp_slop = (long)ostamp - (long)stamp;
+
+ if (nonce_stamp_slop_limit &&
+ abs(nonce_stamp_slop) <= nonce_stamp_slop_limit) {
+ /*
+ * Pretend as if the received nonce (which passes the
+ * HMAC check, so it is not a forged by third-party)
+ * is what we issued.
+ */
+ free((void *)push_cert_nonce);
+ push_cert_nonce = xstrdup(nonce);
+ retval = NONCE_OK;
+ } else {
+ retval = NONCE_SLOP;
+ }
leave:
free(nonce);
+ free(expect);
return retval;
}
@@ -426,6 +494,9 @@ static void prepare_push_cert_sha1(struct child_process *proc)
if (push_cert_nonce) {
argv_array_pushf(&env, "GIT_PUSH_CERT_NONCE=%s", push_cert_nonce);
argv_array_pushf(&env, "GIT_PUSH_CERT_NONCE_STATUS=%s", nonce_status);
+ if (nonce_status == NONCE_SLOP)
+ argv_array_pushf(&env, "GIT_PUSH_CERT_NONCE_SLOP=%ld",
+ nonce_stamp_slop);
}
proc->env = env.argv;
}
@@ -1361,9 +1432,7 @@ static int delete_only(struct command *commands)
int cmd_receive_pack(int argc, const char **argv, const char *prefix)
{
int advertise_refs = 0;
- int stateless_rpc = 0;
int i;
- const char *dir = NULL;
struct command *commands;
struct sha1_array shallow = SHA1_ARRAY_INIT;
struct sha1_array ref = SHA1_ARRAY_INIT;
@@ -1396,21 +1465,21 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
usage(receive_pack_usage);
}
- if (dir)
+ if (service_dir)
usage(receive_pack_usage);
- dir = arg;
+ service_dir = arg;
}
- if (!dir)
+ if (!service_dir)
usage(receive_pack_usage);
setup_path();
- if (!enter_repo(dir, 0))
- die("'%s' does not appear to be a git repository", dir);
+ if (!enter_repo(service_dir, 0))
+ die("'%s' does not appear to be a git repository", service_dir);
git_config(receive_pack_config, NULL);
if (cert_nonce_seed)
- push_cert_nonce = prepare_push_cert_nonce(dir, time(NULL));
+ push_cert_nonce = prepare_push_cert_nonce(service_dir, time(NULL));
if (0 <= transfer_unpack_limit)
unpack_limit = transfer_unpack_limit;