From 37bcc9f3d2f2df0335a42c9692e7d5deafc03514 Mon Sep 17 00:00:00 2001 From: George Kadianakis Date: Mon, 30 Mar 2020 16:09:52 +0300 Subject: [PATCH 1/2] hs-v3: Don't allow registration of an all-zeroes client auth key. The client auth protocol allows attacker-controlled x25519 private keys being passed around, which allows an attacker to potentially trigger the all-zeroes assert for client_auth_sk in hs_descriptor.c:decrypt_descriptor_cookie(). We fixed that by making sure that an all-zeroes client auth key will not be used. There are no guidelines for validating x25519 private keys, and the assert was there as a sanity check for code flow issues (we don't want to enter that function with an unitialized key if client auth is being used). To avoid such crashes in the future, we also changed the assert to a BUG-and-err. --- changes/bug33545 | 4 ++++ src/feature/control/control_hs.c | 9 ++++++++- src/feature/hs/hs_client.h | 2 +- src/test/test_hs_control.c | 14 ++++++++++++++ 4 files changed, 27 insertions(+), 2 deletions(-) create mode 100644 changes/bug33545 diff --git a/changes/bug33545 b/changes/bug33545 new file mode 100644 index 0000000000..c051b01605 --- /dev/null +++ b/changes/bug33545 @@ -0,0 +1,4 @@ + o Minor bugfixes (hidden services): + - Block a client-side assert by disallowing the registration of an x25519 + client auth key that's all zeroes. Fixes bug 33545; bugfix on + 0.4.3.1-alpha. Patch based on patch from "cypherpunks". \ No newline at end of file diff --git a/src/feature/control/control_hs.c b/src/feature/control/control_hs.c index d3cd363f63..f5b331de9a 100644 --- a/src/feature/control/control_hs.c +++ b/src/feature/control/control_hs.c @@ -50,11 +50,18 @@ parse_private_key_from_control_port(const char *client_privkey_str, if (base64_decode((char*)privkey->secret_key, sizeof(privkey->secret_key), key_blob, - strlen(key_blob)) != sizeof(privkey->secret_key)) { + strlen(key_blob)) != sizeof(privkey->secret_key)) { control_printf_endreply(conn, 512, "Failed to decode x25519 private key"); goto err; } + if (fast_mem_is_zero((const char*)privkey->secret_key, + sizeof(privkey->secret_key))) { + control_printf_endreply(conn, 553, + "Invalid private key \"%s\"", key_blob); + goto err; + } + retval = 0; err: diff --git a/src/feature/hs/hs_client.h b/src/feature/hs/hs_client.h index 3660bfa96c..d0a3a7015f 100644 --- a/src/feature/hs/hs_client.h +++ b/src/feature/hs/hs_client.h @@ -45,7 +45,7 @@ typedef enum { REGISTER_SUCCESS_AND_DECRYPTED, /* We failed to register these credentials, because of a bad HS address. */ REGISTER_FAIL_BAD_ADDRESS, - /* We failed to register these credentials, because of a bad HS address. */ + /* We failed to store these credentials in a persistent file on disk. */ REGISTER_FAIL_PERMANENT_STORAGE, } hs_client_register_auth_status_t; diff --git a/src/test/test_hs_control.c b/src/test/test_hs_control.c index 9277711d2a..8ba9f1173c 100644 --- a/src/test/test_hs_control.c +++ b/src/test/test_hs_control.c @@ -467,6 +467,20 @@ test_hs_control_bad_onion_client_auth_add(void *arg) cp1 = buf_get_contents(TO_CONN(&conn)->outbuf, &sz); tt_str_op(cp1, OP_EQ, "512 Failed to decode x25519 private key\r\n"); + tor_free(cp1); + tor_free(args); + + /* Register with an all zero client key */ + args = tor_strdup("jt4grrjwzyz3pjkylwfau5xnjaj23vxmhskqaeyfhrfylelw4hvxcuyd " + "x25519:AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA="); + retval = handle_control_command(&conn, (uint32_t) strlen(args), args); + tt_int_op(retval, OP_EQ, 0); + + /* Check contents */ + cp1 = buf_get_contents(TO_CONN(&conn)->outbuf, &sz); + tt_str_op(cp1, OP_EQ, "553 Invalid private key \"AAAAAAAAAAAAAAAAAAAA" + "AAAAAAAAAAAAAAAAAAAAAAA=\"\r\n"); + client_auths = get_hs_client_auths_map(); tt_assert(!client_auths); From f2f718bca504d0fe1cce566185f8c17e23862335 Mon Sep 17 00:00:00 2001 From: George Kadianakis Date: Mon, 30 Mar 2020 16:33:30 +0300 Subject: [PATCH 2/2] hs-v3: Change all-zeroes hard-assert to a BUG-and-err. And also disallow all-zeroes keys from the filesystem; add a test for it too. --- src/feature/hs/hs_client.c | 7 +++++++ src/feature/hs/hs_descriptor.c | 8 ++++++-- src/test/test_hs_client.c | 4 ++++ 3 files changed, 17 insertions(+), 2 deletions(-) diff --git a/src/feature/hs/hs_client.c b/src/feature/hs/hs_client.c index af8cb0b410..da1202b642 100644 --- a/src/feature/hs/hs_client.c +++ b/src/feature/hs/hs_client.c @@ -2132,6 +2132,13 @@ parse_auth_file_content(const char *client_key_str) "can't be decoded: %s", seckey_b32); goto err; } + + if (fast_mem_is_zero((const char*)auth->enc_seckey.secret_key, + sizeof(auth->enc_seckey.secret_key))) { + log_warn(LD_REND, "Client authorization private key can't be all-zeroes"); + goto err; + } + strncpy(auth->onion_address, onion_address, HS_SERVICE_ADDR_LEN_BASE32); /* We are reading this from the disk, so set the permanent flag anyway. */ diff --git a/src/feature/hs/hs_descriptor.c b/src/feature/hs/hs_descriptor.c index 65d6c7a581..27823aa796 100644 --- a/src/feature/hs/hs_descriptor.c +++ b/src/feature/hs/hs_descriptor.c @@ -1424,10 +1424,14 @@ decrypt_descriptor_cookie(const hs_descriptor_t *desc, tor_assert(!fast_mem_is_zero( (char *) &desc->superencrypted_data.auth_ephemeral_pubkey, sizeof(desc->superencrypted_data.auth_ephemeral_pubkey))); - tor_assert(!fast_mem_is_zero((char *) client_auth_sk, - sizeof(*client_auth_sk))); tor_assert(!fast_mem_is_zero((char *) desc->subcredential, DIGEST256_LEN)); + /* Catch potential code-flow cases of an unitialized private key sneaking + * into this function. */ + if (BUG(fast_mem_is_zero((char *)client_auth_sk, sizeof(*client_auth_sk)))) { + goto done; + } + /* Get the KEYS component to derive the CLIENT-ID and COOKIE-KEY. */ keystream_length = build_descriptor_cookie_keys(desc->subcredential, DIGEST256_LEN, diff --git a/src/test/test_hs_client.c b/src/test/test_hs_client.c index 5f7fe9c404..4d938e4637 100644 --- a/src/test/test_hs_client.c +++ b/src/test/test_hs_client.c @@ -732,6 +732,10 @@ test_parse_auth_file_content(void *arg) /* Bigger key than it should be */ tt_assert(!parse_auth_file_content("xx:descriptor:x25519:" "vjqea4jbhwwc4hto7ekyvqfbeodghbaq6nxi45hz4wr3qvhqv3yqa")); + /* All-zeroes key */ + tt_assert(!parse_auth_file_content("xx:descriptor:x25519:" + "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")); + done: tor_free(auth); }