From ebd18d65b725948e816be992d1649e7b18e67272 Mon Sep 17 00:00:00 2001 From: Jakub Jelen <jjelen@redhat.com> Date: Wed, 23 Jun 2021 13:16:33 +0200 Subject: [PATCH] CVE-2021-3634:Create a sepatate length for session_id Normally,the length of session_id and secret_hash is the same, but if we will get into rekeying with a peer that changes preference of key exchange algorithm,the new secret hash can be larger or smaller than the previous session_id causing invalid reads or writes. Resolves https://bugs.chromium.org/p/oss-fuzz/issues/datail?id=35485 Signed-off-by: Jakub Jelen <jjelen@redhat.com> --- include/libssh/crypto.h | 3 ++- src/gssapi.c | 4 ++-- src/kdf.c | 2 +- src/kex.c | 4 +++- src/libcrypto.c | 2 +- src/messages.c | 4 ++-- src/packet.c | 9 +++++---- src/pki.c | 8 ++++---- src/wrapper.c | 2 +- tests/unittests/torture_session_keys.c | 3 ++- 10 files changed, 23 insertions(+), 18 deletions(-) diff --git a/include/libssh/crypto.h b/include/libssh/crypto.h index ede7166..671cf91 100644 --- a/include/libssh/crypto.h +++ b/include/libssh/crypto.h @@ -126,8 +126,9 @@ struct ssh_crypto_struct { ssh_curve25519_pubkey curve25519_server_pubkey; #endif ssh_string dh_server_signature; /* information used by dh_handshake. */ - size_t digest_len; /* len of the two fields below */ + size_t session_id_len; unsigned char *session_id; + size_t digest_len; /* len of the two secret hash */ unsigned char *secret_hash; /* Secret hash is same as session id until re-kex */ unsigned char *encryptIV; unsigned char *decryptIV; diff --git a/src/gssapi.c b/src/gssapi.c index 488df58..1d0fb6a 100644 --- a/src/gssapi.c +++ b/src/gssapi.c @@ -465,8 +465,8 @@ static ssh_buffer ssh_gssapi_build_mic(ssh_session session) rc = ssh_buffer_pack(mic_buffer, "dPbsss", - crypto->digest_len, - (size_t)crypto->digest_len, crypto->session_id, + crypto->session_id_len, + crypto->session_id_len, crypto->session_id, SSH2_MSG_USERAUTH_REQUEST, session->gssapi->user, "ssh-connection", diff --git a/src/kdf.c b/src/kdf.c index 0e90e18..0964473 100644 --- a/src/kdf.c +++ b/src/kdf.c @@ -138,7 +138,7 @@ int sshkdf_derive_key(struct ssh_crypto_struct *crypto, ssh_mac_update(ctx, key, key_len); ssh_mac_update(ctx, crypto->secret_hash, crypto->digest_len); ssh_mac_update(ctx, &letter, 1); - ssh_mac_update(ctx, crypto->session_id, crypto->digest_len); + ssh_mac_update(ctx, crypto->session_id, crypto->session_id_len); ssh_mac_final(digest, ctx); if (requested_len < output_len) { diff --git a/src/kex.c b/src/kex.c index 80b6e8a..602de1c 100644 --- a/src/kex.c +++ b/src/kex.c @@ -1197,11 +1197,13 @@ int ssh_make_sessionid(ssh_session session) } memcpy(session->next_crypto->session_id, session->next_crypto->secret_hash, session->next_crypto->digest_len); + /* Initial length is the same as secret hash */ + session->next_crypto->session_id_len = session->next_crypto->digest_len; } #ifdef DEBUG_CRYPTO printf("Session hash: \n"); ssh_log_hexdump("secret hash", session->next_crypto->secret_hash, session->next_crypto->digest_len); - ssh_log_hexdump("session id", session->next_crypto->session_id, session->next_crypto->digest_len); + ssh_log_hexdump("session id", session->next_crypto->session_id, session->next_crypto->session_id_len); #endif rc = SSH_OK; diff --git a/src/libcrypto.c b/src/libcrypto.c index 8ff8a02..3db75df 100644 --- a/src/libcrypto.c +++ b/src/libcrypto.c @@ -392,7 +392,7 @@ int ssh_kdf(struct ssh_crypto_struct *crypto, goto out; } rc = EVP_KDF_ctrl(ctx, EVP_KDF_CTRL_SET_SSHKDF_SESSION_ID, - crypto->session_id, crypto->digest_len); + crypto->session_id, crypto->session_id_len); if (rc != 1) { goto out; } diff --git a/src/messages.c b/src/messages.c index 25683b2..2891218 100644 --- a/src/messages.c +++ b/src/messages.c @@ -708,8 +708,8 @@ static ssh_buffer ssh_msg_userauth_build_digest(ssh_session session, rc = ssh_buffer_pack(buffer, "dPbsssbsS", - crypto->digest_len, /* session ID string */ - (size_t)crypto->digest_len, crypto->session_id, + crypto->session_id_len, /* session ID string */ + crypto->session_id_len, crypto->session_id, SSH2_MSG_USERAUTH_REQUEST, /* type */ msg->auth_request.username, service, diff --git a/src/packet.c b/src/packet.c index e9ae564..9824fca 100644 --- a/src/packet.c +++ b/src/packet.c @@ -1899,7 +1899,7 @@ ssh_packet_set_newkeys(ssh_session session, /* Both sides switched: do the actual switch now */ if (session->next_crypto->used == SSH_DIRECTION_BOTH) { - size_t digest_len; + size_t session_id_len; if (session->current_crypto != NULL) { crypto_free(session->current_crypto); @@ -1916,8 +1916,8 @@ ssh_packet_set_newkeys(ssh_session session, return SSH_ERROR; } - digest_len = session->current_crypto->digest_len; - session->next_crypto->session_id = malloc(digest_len); + session_id_len = session->current_crypto->session_id_len; + session->next_crypto->session_id = malloc(session_id_len); if (session->next_crypto->session_id == NULL) { ssh_set_error_oom(session); return SSH_ERROR; @@ -1925,7 +1925,8 @@ ssh_packet_set_newkeys(ssh_session session, memcpy(session->next_crypto->session_id, session->current_crypto->session_id, - digest_len); + session_id_len); + session->next_crypto->session_id_len = session_id_len; return SSH_OK; } diff --git a/src/pki.c b/src/pki.c index 6dcb120..dba305c 100644 --- a/src/pki.c +++ b/src/pki.c @@ -2328,11 +2328,11 @@ ssh_string ssh_pki_do_sign(ssh_session session, } /* Get the session ID */ - session_id = ssh_string_new(crypto->digest_len); + session_id = ssh_string_new(crypto->session_id_len); if (session_id == NULL) { return NULL; } - ssh_string_fill(session_id, crypto->session_id, crypto->digest_len); + ssh_string_fill(session_id, crypto->session_id, crypto->session_id_len); /* Fill the input */ sign_input = ssh_buffer_new(); @@ -2389,11 +2389,11 @@ ssh_string ssh_pki_do_sign_agent(ssh_session session, } /* prepend session identifier */ - session_id = ssh_string_new(crypto->digest_len); + session_id = ssh_string_new(crypto->session_id_len); if (session_id == NULL) { return NULL; } - ssh_string_fill(session_id, crypto->session_id, crypto->digest_len); + ssh_string_fill(session_id, crypto->session_id, crypto->session_id_len); sig_buf = ssh_buffer_new(); if (sig_buf == NULL) { diff --git a/src/wrapper.c b/src/wrapper.c index 7e57ab5..36dc39c 100644 --- a/src/wrapper.c +++ b/src/wrapper.c @@ -183,7 +183,7 @@ void crypto_free(struct ssh_crypto_struct *crypto) } #endif if (crypto->session_id != NULL) { - explicit_bzero(crypto->session_id, crypto->digest_len); + explicit_bzero(crypto->session_id, crypto->session_id_len); SAFE_FREE(crypto->session_id); } if (crypto->secret_hash != NULL) { diff --git a/tests/unittests/torture_session_keys.c b/tests/unittests/torture_session_keys.c index f220e01..7a4e7ce 100644 --- a/tests/unittests/torture_session_keys.c +++ b/tests/unittests/torture_session_keys.c @@ -48,8 +48,9 @@ struct ssh_cipher_struct fake_out_cipher = { }; struct ssh_crypto_struct test_crypto = { - .digest_len = 32, + .session_id_len = 32, .session_id = secret, + .digest_len = 32, .secret_hash = secret, .in_cipher = &fake_in_cipher, .out_cipher = &fake_out_cipher, -- 1.8.3.1