fix(a7-auth): persist dummy key in owner-only sidecar
The store-wide dummy key was regenerated on every credentials_load, so an unknown user's dummy salt changed across daemon restarts while a real user's stored salt stayed stable -- a restart-gated username-enumeration oracle. Persist the 32-byte key in a 0600 <store>.dummykey sidecar next to the credential store. An absent sidecar is created with O_EXCL and fsynced; a present sidecar is read only when it is an owner-only regular file of exactly 32 bytes (otherwise the load fails closed). If the sidecar cannot be created (read-only mount, missing directory) fall back to a transient per-run key with a warning. A NULL store path keeps the key ephemeral.
This commit is contained in:
+149
-2
@@ -70,8 +70,28 @@ static char* make_tmp_file(const char* contents) {
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}
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static void rm_temp(const char* path) {
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if (path)
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unlink(path);
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if (!path)
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return;
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unlink(path);
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/* Every successfully loaded store auto-creates an owner-only
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* `<store>.dummykey` sidecar; remove it too so tests leave no stray key. */
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size_t n = strlen(path) + strlen(".dummykey") + 1;
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char* sidecar = malloc(n);
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if (sidecar) {
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snprintf(sidecar, n, "%s.dummykey", path);
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unlink(sidecar);
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free(sidecar);
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}
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}
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/* `<store>.dummykey` sidecar path (caller frees). */
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static char* dummy_sidecar_path(const char* store_path) {
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size_t n = strlen(store_path) + strlen(".dummykey") + 1;
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char* out = malloc(n);
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if (!out)
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return NULL;
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snprintf(out, n, "%s.dummykey", store_path);
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return out;
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}
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/* Build a valid new-format line for user/password at iters. */
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@@ -745,6 +765,130 @@ static void test_credentials_rejects_group_or_other_accessible() {
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free(path);
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}
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/* Loading a store auto-creates an owner-only `<store>.dummykey` sidecar whose
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* key is stable across reloads, so an unknown-user dummy salt is identical
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* across two loads (the anti-restart enumeration property). */
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static void test_credentials_dummy_key_persisted() {
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char line[CREDENTIAL_MAX_LINE];
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EXPECT_TRUE(make_store_line("alice", KAT_PASSWORD, CREDENTIAL_MIN_ITERS, line, sizeof(line)));
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char contents[CREDENTIAL_MAX_LINE + 2];
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snprintf(contents, sizeof(contents), "%s\n", line);
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char* path = make_tmp_file(contents);
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EXPECT_NOT_NULL(path);
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char* sidecar = dummy_sidecar_path(path);
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EXPECT_NOT_NULL(sidecar);
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char err[512];
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CredentialStore* store = credentials_load(path, NULL, err, sizeof(err));
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EXPECT_NOT_NULL(store);
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struct stat st;
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EXPECT_EQ_INT(stat(sidecar, &st), 0);
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EXPECT_TRUE(S_ISREG(st.st_mode));
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EXPECT_TRUE((st.st_mode & (S_IRWXG | S_IRWXO)) == 0);
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EXPECT_EQ_INT((int)(st.st_mode & 07777), 0600);
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EXPECT_EQ_INT((int)st.st_size, CREDENTIAL_KEY_LEN);
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CredentialVerifier v1;
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EXPECT_TRUE(credentials_get_verifier(store, "unknown-user", NULL, 0, &v1));
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EXPECT_FALSE(v1.found);
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credentials_free(store);
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store = credentials_load(path, NULL, err, sizeof(err));
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EXPECT_NOT_NULL(store);
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CredentialVerifier v2;
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EXPECT_TRUE(credentials_get_verifier(store, "unknown-user", NULL, 0, &v2));
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EXPECT_FALSE(v2.found);
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EXPECT_TRUE(memcmp(v1.salt, v2.salt, sizeof(v1.salt)) == 0);
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credentials_free(store);
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rm_temp(path);
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free(path);
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free(sidecar);
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}
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/* A sidecar that is group/other accessible, the wrong size, or not a regular
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* file must fail the load closed. */
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static void test_credentials_dummy_key_rejects_bad_sidecar() {
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char err[512];
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char line[CREDENTIAL_MAX_LINE];
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EXPECT_TRUE(make_store_line("alice", KAT_PASSWORD, CREDENTIAL_MIN_ITERS, line, sizeof(line)));
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char contents[CREDENTIAL_MAX_LINE + 2];
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snprintf(contents, sizeof(contents), "%s\n", line);
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/* Group/other permission bits on the sidecar. */
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char* path = make_tmp_file(contents);
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EXPECT_NOT_NULL(path);
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char* sidecar = dummy_sidecar_path(path);
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EXPECT_NOT_NULL(sidecar);
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uint8_t key[CREDENTIAL_KEY_LEN];
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memset(key, 0x5a, sizeof(key));
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FILE* fp = fopen(sidecar, "wb");
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EXPECT_NOT_NULL(fp);
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EXPECT_TRUE(fwrite(key, 1, sizeof(key), fp) == sizeof(key));
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fclose(fp);
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EXPECT_EQ_INT(chmod(sidecar, 0640), 0);
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EXPECT_NULL(credentials_load(path, NULL, err, sizeof(err)));
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EXPECT_TRUE(err[0] != '\0');
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rm_temp(path);
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free(path);
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free(sidecar);
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/* Wrong size (not exactly 32 bytes). */
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path = make_tmp_file(contents);
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EXPECT_NOT_NULL(path);
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sidecar = dummy_sidecar_path(path);
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EXPECT_NOT_NULL(sidecar);
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fp = fopen(sidecar, "wb");
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EXPECT_NOT_NULL(fp);
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EXPECT_TRUE(fwrite(key, 1, CREDENTIAL_SALT_LEN, fp) == CREDENTIAL_SALT_LEN);
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fclose(fp);
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EXPECT_EQ_INT(chmod(sidecar, 0600), 0);
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EXPECT_NULL(credentials_load(path, NULL, err, sizeof(err)));
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EXPECT_TRUE(err[0] != '\0');
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rm_temp(path);
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free(path);
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free(sidecar);
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/* Non-regular file (a directory at the sidecar path). */
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path = make_tmp_file(contents);
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EXPECT_NOT_NULL(path);
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sidecar = dummy_sidecar_path(path);
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EXPECT_NOT_NULL(sidecar);
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EXPECT_EQ_INT(mkdir(sidecar, 0700), 0);
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EXPECT_NULL(credentials_load(path, NULL, err, sizeof(err)));
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EXPECT_TRUE(err[0] != '\0');
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rmdir(sidecar);
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rm_temp(path);
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free(path);
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free(sidecar);
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}
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/* A NULL store path has nowhere to persist a key, so each load gets a fresh
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* ephemeral key (and creates no sidecar). */
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static void test_credentials_dummy_key_null_store_ephemeral() {
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char err[512];
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CredentialStore* store = credentials_load(NULL, NULL, err, sizeof(err));
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EXPECT_NOT_NULL(store);
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CredentialVerifier v1;
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CredentialVerifier v1b;
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EXPECT_TRUE(credentials_get_verifier(store, "nobody", NULL, 0, &v1));
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EXPECT_FALSE(v1.found);
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/* Within one store the dummy challenge is still deterministic. */
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EXPECT_TRUE(credentials_get_verifier(store, "nobody", NULL, 0, &v1b));
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EXPECT_TRUE(memcmp(v1.salt, v1b.salt, sizeof(v1.salt)) == 0);
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credentials_free(store);
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store = credentials_load(NULL, NULL, err, sizeof(err));
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EXPECT_NOT_NULL(store);
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CredentialVerifier v2;
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EXPECT_TRUE(credentials_get_verifier(store, "nobody", NULL, 0, &v2));
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/* No persistence path, so the second load's random key differs (and with it
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* the dummy salt). */
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EXPECT_TRUE(memcmp(v1.salt, v2.salt, sizeof(v1.salt)) != 0);
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credentials_free(store);
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}
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static void test_credentials_burn() {
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char secret[32];
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memcpy(secret, "supersecretvalue", 17);
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@@ -777,5 +921,8 @@ void test_credentials(void) {
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test_credentials_read_secret_file_bad();
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test_credentials_hash_file();
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test_credentials_rejects_group_or_other_accessible();
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test_credentials_dummy_key_persisted();
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test_credentials_dummy_key_rejects_bad_sidecar();
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test_credentials_dummy_key_null_store_ephemeral();
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test_credentials_burn();
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}
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