On 13/06/2019 15:48, Arne Schwabe wrote:
> The previous auth-token implementation had a serious problem, especially when
> paired with an unpatched OpenVPN client that keeps trying the auth-token
> (commit e61b401a).
>
> The auth-token-gen implementation forgot the auth-token on reconnect, this
> lead to reconnect with auth-token never working.
>
> This new implementation implements the auth-token in a stateles variant. By
> using HMAC to sign the auth-token the server can verify if a token has been
> authenticated and by checking the embedded timestamp in the token it can
> also verify that the auth-token is still valid.
>
> Using the new config directive auth-gen-token-secret instead of
> extending auth-gen-token (--auth-gen-token [lifetime] [secret-key]) was
> chosen to allow inlinening the secret key.
>
> Patch V2: cleaned up code, use refactored read_pem_key_file function
> Patch V3: clarify some design decision in the commit message
> Patch V4: Use ephermal_generate_key
> ---
> doc/openvpn.8 | 25 ++++
> src/openvpn/Makefile.am | 1 +
> src/openvpn/auth_token.c | 272 +++++++++++++++++++++++++++++++++++++++
> src/openvpn/auth_token.h | 116 +++++++++++++++++
> src/openvpn/init.c | 30 ++++-
> src/openvpn/openvpn.h | 1 +
> src/openvpn/options.c | 22 +++-
> src/openvpn/options.h | 4 +
> src/openvpn/push.c | 70 ++++++++--
> src/openvpn/push.h | 8 ++
> src/openvpn/ssl.c | 7 +-
> src/openvpn/ssl_common.h | 36 ++++--
> src/openvpn/ssl_verify.c | 182 ++++++++++++--------------
> 13 files changed, 639 insertions(+), 135 deletions(-)
> create mode 100644 src/openvpn/auth_token.c
> create mode 100644 src/openvpn/auth_token.h
>
Not as heavy tested as in last round, but changes has been applied as
indicated. Thank you! Unfortunately, some compiler warnings are appearing:
------------------------------------------------------------
auth_token.c: In function ‘generate_auth_token’:
auth_token.c:115:9: warning: dereferencing type-punned pointer will break
strict-aliasing rules [-Wstrict-aliasing]
initial_timestamp = *((uint64_t *)(old_tstamp_decode));
^
auth_token.c: In function ‘verify_auth_token’:
auth_token.c:233:9: warning: format ‘%lld’ expects argument of type ‘long long
int’, but argument 3 has type ‘uint64_t’ [-Wformat=]
msg(M_WARN, "Initial timestamp (%lld) in token from client earlier
than "
^
auth_token.c:233:9: warning: format ‘%lld’ expects argument of type ‘long long
int’, but argument 4 has type ‘uint64_t’ [-Wformat=]
------------------------------------------------------------
The first one (dereferencing type-punned pointer) seems to only show up with
gcc-4.8.5 and 6.3.1. Below are warnings reported by both gcc-7.3.1 and 8.3.1,
which are also a bit more verbose, with a few additional twists.
------------------------------------------------------------
auth_token.c: In function ‘verify_auth_token’:
auth_token.c:233:21: warning: format ‘%lld’ expects argument of type ‘long long
int’, but argument 3 has type ‘uint64_t’ {aka ‘long unsigned int’} [-Wformat=]
msg(M_WARN, "Initial timestamp (%lld) in token from client earlier
than "
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
auth_token.c:235:13:
timestamp_initial, timestamp);
~~~~~~~~~~~~~~~~~
error.h:151:67: note: in definition of macro ‘msg’
#define msg(flags, ...) do { if (msg_test(flags)) {x_msg((flags),
__VA_ARGS__);} EXIT_FATAL(flags); } while (false)
^~~~~~~~~~~
auth_token.c:233:44: note: format string is defined here
msg(M_WARN, "Initial timestamp (%lld) in token from client earlier
than "
~~~^
%ld
In file included from buffer.h:28,
from auth_token.c:10:
auth_token.c:233:21: warning: format ‘%lld’ expects argument of type ‘long long
int’, but argument 4 has type ‘uint64_t’ {aka ‘long unsigned int’} [-Wformat=]
msg(M_WARN, "Initial timestamp (%lld) in token from client earlier
than "
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
auth_token.c:235:32:
timestamp_initial, timestamp);
~~~~~~~~~
error.h:151:67: note: in definition of macro ‘msg’
#define msg(flags, ...) do { if (msg_test(flags)) {x_msg((flags),
__VA_ARGS__);} EXIT_FATAL(flags); } while (false)
^~~~~~~~~~~
auth_token.c:234:36: note: format string is defined here
"current timestamp (%lld). Broken/unsynchronised clock?",
~~~^
%ld
------------------------------------------------------------
Other than these issues, things looks good and would normally get an ACK.
--
kind regards,
David Sommerseth
OpenVPN Inc
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