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[Openvpn-devel] [PATCH v4] Add 'allow-compression stub-only' internally for DCO
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From: Arne S. <ar...@rf...> - 2023-03-24 10:06:56
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This changes the "no" setting of allow-compression to also refuse framing.
This is important for our DCO implementation as these do not implement framing.
This behaviour surfaced when a commercial VPN provider was pushing
"comp-lzo no" to a client with DCO. While we are technically at fault here
for announcing comp-lzo no support by announcing IV_LZO_STUB=1, the
VPN provider continues to push "comp-lzo no" even in absense of that
flag.
As the new default we default to allow-compression stub-only if a stub option
is found in the config and to allow-compression no otherwise. This ensures
that we only enable DCO when no compression framing is used.
This will now also bail out if the server pushes a compression setting that
we do not support as mismatching compression is almost never a working
connection. In my lz4-v2 and lzo-v2 you might have a connection that works
mostly but some packets will be dropped since they compressed which is not
desirable either since it becomes very hard to debug.
Patch v2: bail out if server pushes an unsupported method. Also include this
bail out logic when OpenVPN is compiled without compression support.
Patch v3: always parse all compression option and move logic to check method
Patch v4: fix for not setting correct default for non-dco
Change-Id: Ibd0c77af24e2214b3055d585dc23a4b06dccd414
Signed-off-by: Arne Schwabe <ar...@rf...>
---
doc/man-sections/protocol-options.rst | 4 ++-
src/openvpn/comp.c | 47 ++++++++++++++++++---------
src/openvpn/comp.h | 2 +-
src/openvpn/options.c | 14 ++++++--
4 files changed, 46 insertions(+), 21 deletions(-)
diff --git a/doc/man-sections/protocol-options.rst b/doc/man-sections/protocol-options.rst
index 248f65cfd..055d08f95 100644
--- a/doc/man-sections/protocol-options.rst
+++ b/doc/man-sections/protocol-options.rst
@@ -25,7 +25,9 @@ configured in a compatible way between both the local and remote side.
compression at the same time is not a feasible option.
:code:`no` (default)
- OpenVPN will refuse any non-stub compression.
+ OpenVPN will refuse any compression. If data-channel offloading
+ is enabled. OpenVPN will additionally also refuse compression
+ framing (stub).
:code:`yes`
OpenVPN will send and receive compressed packets.
diff --git a/src/openvpn/comp.c b/src/openvpn/comp.c
index d6d8029da..c7a562f5a 100644
--- a/src/openvpn/comp.c
+++ b/src/openvpn/comp.c
@@ -134,36 +134,51 @@ comp_print_stats(const struct compress_context *compctx, struct status_output *s
void
comp_generate_peer_info_string(const struct compress_options *opt, struct buffer *out)
{
- if (opt)
+ if (!opt || opt->flags & COMP_F_ALLOW_NOCOMP_ONLY)
+ {
+ return;
+ }
+
+ bool lzo_avail = false;
+ if (!(opt->flags & COMP_F_ADVERTISE_STUBS_ONLY))
{
- bool lzo_avail = false;
- if (!(opt->flags & COMP_F_ADVERTISE_STUBS_ONLY))
- {
#if defined(ENABLE_LZ4)
- buf_printf(out, "IV_LZ4=1\n");
- buf_printf(out, "IV_LZ4v2=1\n");
+ buf_printf(out, "IV_LZ4=1\n");
+ buf_printf(out, "IV_LZ4v2=1\n");
#endif
#if defined(ENABLE_LZO)
- buf_printf(out, "IV_LZO=1\n");
- lzo_avail = true;
+ buf_printf(out, "IV_LZO=1\n");
+ lzo_avail = true;
#endif
- }
- if (!lzo_avail)
- {
- buf_printf(out, "IV_LZO_STUB=1\n");
- }
- buf_printf(out, "IV_COMP_STUB=1\n");
- buf_printf(out, "IV_COMP_STUBv2=1\n");
}
+ if (!lzo_avail)
+ {
+ buf_printf(out, "IV_LZO_STUB=1\n");
+ }
+ buf_printf(out, "IV_COMP_STUB=1\n");
+ buf_printf(out, "IV_COMP_STUBv2=1\n");
}
bool
check_compression_settings_valid(struct compress_options *info, int msglevel)
{
+ /*
+ * We also allow comp-stub-v2 here as it technically allows escaping of
+ * weird mac address and IPv5 protocol but practically always is used
+ * as an way to disable all framing.
+ */
+ if (info->alg != COMP_ALGV2_UNCOMPRESSED && info->alg != COMP_ALG_UNDEF
+ && (info->flags & COMP_F_ALLOW_NOCOMP_ONLY))
+ {
+ msg(msglevel, "Compression or compression stub framing is not allowed "
+ "since data-channel offloading is enabled.");
+ return false;
+ }
+
if ((info->flags & COMP_F_ALLOW_STUB_ONLY) && comp_non_stub_enabled(info))
{
msg(msglevel, "Compression is not allowed since allow-compression is "
- "set to 'no'");
+ "set to 'stub-only'");
return false;
}
#ifndef ENABLE_LZ4
diff --git a/src/openvpn/comp.h b/src/openvpn/comp.h
index 8636727ab..71b350d09 100644
--- a/src/openvpn/comp.h
+++ b/src/openvpn/comp.h
@@ -60,7 +60,7 @@
* we still accept other compressions to be pushed */
#define COMP_F_MIGRATE (1<<5) /* push stub-v2 or comp-lzo no when we see a client with comp-lzo in occ */
#define COMP_F_ALLOW_ASYM (1<<6) /* Compression was explicitly set to allow asymetric compression */
-
+#define COMP_F_ALLOW_NOCOMP_ONLY (1<<7) /* Do not allow compression framing (breaks DCO) */
/*
* Length of prepended prefix on compressed packets
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 435e1ca9e..0ccff7213 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -3644,10 +3644,12 @@ options_set_backwards_compatible_options(struct options *o)
*
* Disable compression by default starting with 2.6.0 if no other
* compression related option has been explicitly set */
- if (!comp_non_stub_enabled(&o->comp) && !need_compatibility_before(o, 20600)
- && (o->comp.flags == 0))
+ if (!need_compatibility_before(o, 20600) && (o->comp.flags == 0))
{
- o->comp.flags = COMP_F_ALLOW_STUB_ONLY|COMP_F_ADVERTISE_STUBS_ONLY;
+ if (!comp_non_stub_enabled(&o->comp))
+ {
+ o->comp.flags = COMP_F_ALLOW_STUB_ONLY | COMP_F_ADVERTISE_STUBS_ONLY;
+ }
}
#endif
}
@@ -3749,6 +3751,12 @@ options_postprocess_mutate(struct options *o, struct env_set *es)
o->tuntap_options.disable_dco = !dco_check_option(D_DCO, o)
|| !dco_check_startup_option(D_DCO, o);
}
+#ifdef USE_COMP
+ if (dco_enabled(o))
+ {
+ o->comp.flags |= COMP_F_ALLOW_NOCOMP_ONLY;
+ }
+#endif
#ifdef _WIN32
if (dco_enabled(o))
--
2.37.1 (Apple Git-137.1)
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