| Message ID | 20201008115959.21151-1-arne@rfc2549.org |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [Openvpn-devel,v3] Allow 'none' cipher being specified in --data-ciphers | expand |
Acked-by: Gert Doering <gert@greenie.muc.de> I have added two new cases to my server test suite: client with "--data-ciphers none" and "--ncp-disable --cipher none", against a server instance that permits "none" as part of its data-ciphers. The first case failed on the client side ("unrecognized cipher: none"), the second case was refused by the server side ("No common cipher... client supports cipher '[null-cipher]'). Of course the server side *also* needs the patch to accept "none" as part of --data-ciphers :-) Then, this works: 2020-10-04 15:04:28 us=208824 2001:608:4:0:669a:56c1:4175:2c5b peer info: IV_CIPHERS=none 2020-10-04 15:04:28 us=251968 Data Channel: using negotiated cipher 'none' 2020-10-04 15:04:28 us=252006 ******* WARNING *******: '--cipher none' was ... The warning in the logs is very clear and explicit - and I think this is good. This is a very special-use setting, and should only be used with sufficient information and consideration. Big IPv4 packets (t_client test with 3000 bytes) do not work - something is wrong in our mtu/overhead calcululation. But this is not something new (as the v3 commit message rightly points out) - if I do "client connects with --data-cipher DES-EDE3-CBC" (non AEAD) I get the same TCP/UDP packet too large on write to ... (tried=1544,max=1542) error as I have with "none" (there, it is tried=1529,max=1526). Strange enough this only happens for IPv4 packets. Your patch has been applied to the master and release/2.5 branch. commit c018fc00be25aee5921d234531f87753a3a7aec7 (master) commit f308251acdc539acb370aeccf46b0ec5587129c1 (release/2.5) Author: Arne Schwabe Date: Thu Oct 8 13:59:59 2020 +0200 Allow 'none' cipher being specified in --data-ciphers Signed-off-by: Arne Schwabe <arne@rfc2549.org> Acked-by: Gert Doering <gert@greenie.muc.de> Message-Id: <20201008115959.21151-1-arne@rfc2549.org> URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21181.html Signed-off-by: Gert Doering <gert@greenie.muc.de> -- kind regards, Gert Doering
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c index 3535fc72..f90c6a85 100644 --- a/src/openvpn/ssl.c +++ b/src/openvpn/ssl.c @@ -2554,6 +2554,14 @@ key_method_2_read(struct buffer *buf, struct tls_multi *multi, struct tls_sessio multi->remote_ciphername = options_string_extract_option(options, "cipher", NULL); + /* In OCC we send '[null-cipher]' instead 'none' */ + if (multi->remote_ciphername + && strcmp(multi->remote_ciphername, "[null-cipher]") == 0) + { + free(multi->remote_ciphername); + multi->remote_ciphername = string_alloc("none", NULL); + } + if (tls_session_user_pass_enabled(session)) { /* Perform username/password authentication */ diff --git a/src/openvpn/ssl_ncp.c b/src/openvpn/ssl_ncp.c index 55496395..c8229044 100644 --- a/src/openvpn/ssl_ncp.c +++ b/src/openvpn/ssl_ncp.c @@ -110,7 +110,15 @@ mutate_ncp_cipher_list(const char *list, struct gc_arena *gc) * e.g. replacing AeS-128-gCm with AES-128-GCM */ const cipher_kt_t *ktc = cipher_kt_get(token); - if (!ktc) + if (strcmp(token, "none") == 0) + { + msg(M_WARN, "WARNING: cipher 'none' specified for --data-ciphers. " + "This allows negotiation of NO encryption and " + "tunnelled data WILL then be transmitted in clear text " + "over the network! " + "PLEASE DO RECONSIDER THIS SETTING!"); + } + if (!ktc && strcmp(token, "none")!= 0) { msg(M_WARN, "Unsupported cipher in --data-ciphers: %s", token); error_found = true; @@ -118,6 +126,12 @@ mutate_ncp_cipher_list(const char *list, struct gc_arena *gc) else { const char *ovpn_cipher_name = cipher_kt_name(ktc); + if (ktc == NULL) + { + /* NULL resolves to [null-cipher] but we need none for + * data-ciphers */ + ovpn_cipher_name = "none"; + } if (buf_len(&new_list)> 0) { diff --git a/tests/unit_tests/openvpn/test_ncp.c b/tests/unit_tests/openvpn/test_ncp.c index a4334c89..4077be5e 100644 --- a/tests/unit_tests/openvpn/test_ncp.c +++ b/tests/unit_tests/openvpn/test_ncp.c @@ -50,7 +50,9 @@ test_check_ncp_ciphers_list(void **state) struct gc_arena gc = gc_new(); bool have_chacha = cipher_kt_get("CHACHA20-POLY1305"); - + assert_string_equal(mutate_ncp_cipher_list("none", &gc), "none"); + assert_string_equal(mutate_ncp_cipher_list("AES-256-GCM:none", &gc), + "AES-256-GCM:none"); assert_string_equal(mutate_ncp_cipher_list(aes_ciphers, &gc), aes_ciphers); @@ -139,7 +141,7 @@ test_poor_man(void **state) char *best_cipher; const char *serverlist = "CHACHA20_POLY1305:AES-128-GCM"; - const char *serverlistbfcbc = "CHACHA20_POLY1305:AES-128-GCM:BF-CBC"; + const char *serverlistbfcbc = "CHACHA20_POLY1305:AES-128-GCM:BF-CBC:none"; best_cipher = ncp_get_best_cipher(serverlist, "IV_YOLO=NO\nIV_BAR=7", @@ -166,6 +168,14 @@ test_poor_man(void **state) assert_string_equal(best_cipher, "AES-128-GCM"); + best_cipher = ncp_get_best_cipher(serverlist, NULL, + "none", &gc); + assert_ptr_equal(best_cipher, NULL); + + best_cipher = ncp_get_best_cipher(serverlistbfcbc, NULL, + "none", &gc); + assert_string_equal(best_cipher, "none"); + best_cipher = ncp_get_best_cipher(serverlist, NULL,NULL, &gc); assert_ptr_equal(best_cipher, NULL);
Although we want to get rid of none as cipher, we still have not deprecated it. In order to use it currently you need --ncp-disable together with --cipher none to use the none cipher otherwise OpenVPN will spit out an error about an unrecognised cipher in --data-ciphers. In our current situation allowing none to be specified in data-ciphers is the lesser evil. This commit also fixes that we use '[null-cipher]' instead 'none' when setting remote_cipher. Note that negotiating to cipher 'none' can the same the same problems with frame size calculation as any other non AEAD cipher. If --cipher none is also specified in the configuration, the workaround of commit e539c95dc will also apply to cipher none. Patch V2: Also work correctly if remote_cipher is NULL. Patch V3: fix unit tests, add note about corner case Signed-off-by: Arne Schwabe <arne@rfc2549.org> --- src/openvpn/ssl.c | 8 ++++++++ src/openvpn/ssl_ncp.c | 16 +++++++++++++++- tests/unit_tests/openvpn/test_ncp.c | 14 ++++++++++++-- 3 files changed, 35 insertions(+), 3 deletions(-)