Hi,
On 30-11-2020 13:38, 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.
>
> Patch V2: use correct length for TLS-Crypt v2, use length variable
> non-tlscryptv2 test
>
> Signed-off-by: Arne Schwabe <a...@rfc2549.org>
> ---
> src/openvpn/ps.c | 34 +++++++++++++++++++++++++++++-----
> 1 file changed, 29 insertions(+), 5 deletions(-)
>
> diff --git a/src/openvpn/ps.c b/src/openvpn/ps.c
> index 2089e6b9..5d760782 100644
> --- a/src/openvpn/ps.c
> +++ b/src/openvpn/ps.c
> @@ -983,14 +983,38 @@ 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));
> + int plen = (p[0] << 8) | p[1];
> +
> + if (p[2] == (P_CONTROL_HARD_RESET_CLIENT_V3 << P_OPCODE_SHIFT))
> + {
> + /* WKc is at least 290 byte (not including metadata):
> + *
> + * 16 bit len + 256 bit HMAC + 2048 bit Kc = 2320 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.
> + */
> + return (plen >= 336 && plen < (1024 + 255));
> + }
> + else
> + {
> + /* For non tls-crypt2 we assume the packet length to valid
> between
> + * 14 and 255 */
> + return plen >= 14 && plen <= 255
> + && (p[2] == (P_CONTROL_HARD_RESET_CLIENT_V2 <<
> P_OPCODE_SHIFT));
> + }
> }
> else if (len >= 2)
> {
> - return p[0] == 0 && p[1] >= 14;
> + int plen = (p[0] << 8) | p[1];
> + return plen >= 14 && plen <= 255;
> }
> else
> {
>
Thanks. This looks good to me now.
Ran some tests to check that this correctly resolves the issue when
using --tls-crypt-v2 in combination with --port-share.
Acked-by: Steffan Karger <stef...@karger.me>
-Steffan
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