| Message ID | 20201120160418.17690-1-arne@rfc2549.org |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | [Openvpn-devel] Fix port-share option with TLS-Crypt v2 | expand |
Hi, On 20-11-2020 17:04, Arne Schwabe wrote: > The port-share option assumed that all openvpn initial reset packets > are between 14 and 255 bytes long. This is not true for tls-crypt-v2. Good catch, I totally missed this in the tls-crypt-v2 patch set. > --- > src/openvpn/ps.c | 34 ++++++++++++++++++++++++++++++---- > 1 file changed, 30 insertions(+), 4 deletions(-) > > diff --git a/src/openvpn/ps.c b/src/openvpn/ps.c > index 2089e6b9..cd00bc23 100644 > --- a/src/openvpn/ps.c > +++ b/src/openvpn/ps.c > @@ -983,10 +983,36 @@ is_openvpn_protocol(const struct buffer *buf) > const int len = BLEN(buf); > if (len >= 3) > { > - return p[0] == 0 > - && p[1] >= 14 > - && (p[2] == (P_CONTROL_HARD_RESET_CLIENT_V2 << P_OPCODE_SHIFT) > - || p[2] == (P_CONTROL_HARD_RESET_CLIENT_V3 << P_OPCODE_SHIFT)); > + if (p[2] == (P_CONTROL_HARD_RESET_CLIENT_V3 << P_OPCODE_SHIFT)) > + { > + /* WKc is at least 306 byte (not including metadata): > + * > + * 16 bit len + 256 bit HMAC + 128 bit IV + 2048 bit Kc = 2448 bit The IV is part of the HMAC, so does not need to be counted here. So this this be 2320 bits / 290 bytes. > + * > + * This is increased by the normal length of client handshake + > + * tls-crypt overhead (32) > + * > + * For metadata tls-crypt-v2.txt does not explicitly specify > + * an upper limit but we also have TLS_CRYPT_V2_MAX_WKC_LEN > + * as 1024 bytes. We err on the safe side with 255 extra overhead > + * > + * We don't do the 2 byte check for tls-crypt-v2 because it is very > + * unrealistic to have only 2 bytes available. > + */ > + int plen = (p[0] << 8) | p[1]; > + > + return (plen >= 352 && plen < (1024 + 255)); > + } > + else > + { > + /* first two bytes are the size field. This is an openvpn packet > + * between 14 bytes and 255 (otherwise p[1] would be 01 or larger. > + * on the hard reset packet key_id is zero, so only the opcode > + * part is non-null */ Instead of explaining the length field in the comment, why not just move the "int plen = (p[0] << 8) | p[1];" outside the if to have the code explain that by itself? > + return p[0] == 0 > + && p[1] >= 14 > + && (p[2] == (P_CONTROL_HARD_RESET_CLIENT_V2 << P_OPCODE_SHIFT)); > + } > } > else if (len >= 2) > { > Thanks, -Steffan
diff --git a/src/openvpn/ps.c b/src/openvpn/ps.c index 2089e6b9..cd00bc23 100644 --- a/src/openvpn/ps.c +++ b/src/openvpn/ps.c @@ -983,10 +983,36 @@ is_openvpn_protocol(const struct buffer *buf) const int len = BLEN(buf); if (len >= 3) { - return p[0] == 0 - && p[1] >= 14 - && (p[2] == (P_CONTROL_HARD_RESET_CLIENT_V2 << P_OPCODE_SHIFT) - || p[2] == (P_CONTROL_HARD_RESET_CLIENT_V3 << P_OPCODE_SHIFT)); + if (p[2] == (P_CONTROL_HARD_RESET_CLIENT_V3 << P_OPCODE_SHIFT)) + { + /* WKc is at least 306 byte (not including metadata): + * + * 16 bit len + 256 bit HMAC + 128 bit IV + 2048 bit Kc = 2448 bit + * + * This is increased by the normal length of client handshake + + * tls-crypt overhead (32) + * + * For metadata tls-crypt-v2.txt does not explicitly specify + * an upper limit but we also have TLS_CRYPT_V2_MAX_WKC_LEN + * as 1024 bytes. We err on the safe side with 255 extra overhead + * + * We don't do the 2 byte check for tls-crypt-v2 because it is very + * unrealistic to have only 2 bytes available. + */ + int plen = (p[0] << 8) | p[1]; + + return (plen >= 352 && plen < (1024 + 255)); + } + else + { + /* first two bytes are the size field. This is an openvpn packet + * between 14 bytes and 255 (otherwise p[1] would be 01 or larger. + * on the hard reset packet key_id is zero, so only the opcode + * part is non-null */ + return p[0] == 0 + && p[1] >= 14 + && (p[2] == (P_CONTROL_HARD_RESET_CLIENT_V2 << P_OPCODE_SHIFT)); + } } else if (len >= 2) {