From: Arne Schwabe <a...@rfc2549.org>
This makes OpenVPN more picky in accepting control message in two aspects:
- Characters are checked in the whole buffer and not until the first
NUL byte
- if the message contains invalid characters, we no longer continue
evaluating a fixed up version of the message but rather stop
processing it completely.
Previously it was possible to get invalid characters to end up in log
files or on a terminal.
This also prepares the logic a bit in the direction of having a proper
framing of control messages separated by null bytes instead of relying
on the TLS framing for that. All OpenVPN implementations write the 0
bytes between control commands.
This patch also include several improvement suggestion from Reynir
(thanks!).
CVE: 2024-5594
Reported-By: Reynir Bj�rnsson <rey...@reynir.dk>
Change-Id: I0d926f910637dabc89bf5fa919dc6beef1eb46d9
Signed-off-by: Arne Schwabe <a...@rfc2549.org>
Acked-by: Antonio Quartulli <a...@unstable.cc>
---
src/openvpn/buffer.c | 17 ++++
src/openvpn/buffer.h | 12 +++
src/openvpn/forward.c | 123 ++++++++++++++++---------
tests/unit_tests/openvpn/test_buffer.c | 24 +++++
4 files changed, 132 insertions(+), 44 deletions(-)
diff --git a/src/openvpn/buffer.c b/src/openvpn/buffer.c
index 3a8069c56..abe6a9c89 100644
--- a/src/openvpn/buffer.c
+++ b/src/openvpn/buffer.c
@@ -1087,6 +1087,23 @@ string_mod(char *str, const unsigned int inclusive,
const unsigned int exclusive
return ret;
}
+bool
+string_check_buf(struct buffer *buf, const unsigned int inclusive, const
unsigned int exclusive)
+{
+ ASSERT(buf);
+
+ for (int i = 0; i < BLEN(buf); i++)
+ {
+ char c = BSTR(buf)[i];
+
+ if (!char_inc_exc(c, inclusive, exclusive))
+ {
+ return false;
+ }
+ }
+ return true;
+}
+
const char *
string_mod_const(const char *str,
const unsigned int inclusive,
diff --git a/src/openvpn/buffer.h b/src/openvpn/buffer.h
index 27c319952..8a40010bc 100644
--- a/src/openvpn/buffer.h
+++ b/src/openvpn/buffer.h
@@ -943,6 +943,18 @@ bool string_class(const char *str, const unsigned int
inclusive, const unsigned
*/
bool string_mod(char *str, const unsigned int inclusive, const unsigned int
exclusive, const char replace);
+
+/**
+ * Check a buffer if it only consists of allowed characters.
+ *
+ * @param buf The buffer to be checked.
+ * @param inclusive The character classes that are allowed.
+ * @param exclusive Character classes that are not allowed even if they are
also in inclusive.
+ * @return True if the string consists only of allowed characters, false
otherwise.
+ */
+bool
+string_check_buf(struct buffer *buf, const unsigned int inclusive, const
unsigned int exclusive);
+
/**
* Returns a copy of a string with certain classes of characters of it
replaced with a specified
* character.
diff --git a/src/openvpn/forward.c b/src/openvpn/forward.c
index 01165b2ed..ef35bc619 100644
--- a/src/openvpn/forward.c
+++ b/src/openvpn/forward.c
@@ -230,6 +230,51 @@ check_tls(struct context *c)
}
}
+static void
+parse_incoming_control_channel_command(struct context *c, struct buffer *buf)
+{
+ if (buf_string_match_head_str(buf, "AUTH_FAILED"))
+ {
+ receive_auth_failed(c, buf);
+ }
+ else if (buf_string_match_head_str(buf, "PUSH_"))
+ {
+ incoming_push_message(c, buf);
+ }
+ else if (buf_string_match_head_str(buf, "RESTART"))
+ {
+ server_pushed_signal(c, buf, true, 7);
+ }
+ else if (buf_string_match_head_str(buf, "HALT"))
+ {
+ server_pushed_signal(c, buf, false, 4);
+ }
+ else if (buf_string_match_head_str(buf, "INFO_PRE"))
+ {
+ server_pushed_info(c, buf, 8);
+ }
+ else if (buf_string_match_head_str(buf, "INFO"))
+ {
+ server_pushed_info(c, buf, 4);
+ }
+ else if (buf_string_match_head_str(buf, "CR_RESPONSE"))
+ {
+ receive_cr_response(c, buf);
+ }
+ else if (buf_string_match_head_str(buf, "AUTH_PENDING"))
+ {
+ receive_auth_pending(c, buf);
+ }
+ else if (buf_string_match_head_str(buf, "EXIT"))
+ {
+ receive_exit_message(c);
+ }
+ else
+ {
+ msg(D_PUSH_ERRORS, "WARNING: Received unknown control message: %s",
BSTR(buf));
+ }
+}
+
/*
* Handle incoming configuration
* messages on the control channel.
@@ -245,51 +290,41 @@ check_incoming_control_channel(struct context *c)
struct buffer buf = alloc_buf_gc(len, &gc);
if (tls_rec_payload(c->c2.tls_multi, &buf))
{
- /* force null termination of message */
- buf_null_terminate(&buf);
-
- /* enforce character class restrictions */
- string_mod(BSTR(&buf), CC_PRINT, CC_CRLF, 0);
- if (buf_string_match_head_str(&buf, "AUTH_FAILED"))
+ while (BLEN(&buf) > 1)
{
- receive_auth_failed(c, &buf);
- }
- else if (buf_string_match_head_str(&buf, "PUSH_"))
- {
- incoming_push_message(c, &buf);
- }
- else if (buf_string_match_head_str(&buf, "RESTART"))
- {
- server_pushed_signal(c, &buf, true, 7);
- }
- else if (buf_string_match_head_str(&buf, "HALT"))
- {
- server_pushed_signal(c, &buf, false, 4);
- }
- else if (buf_string_match_head_str(&buf, "INFO_PRE"))
- {
- server_pushed_info(c, &buf, 8);
- }
- else if (buf_string_match_head_str(&buf, "INFO"))
- {
- server_pushed_info(c, &buf, 4);
- }
- else if (buf_string_match_head_str(&buf, "CR_RESPONSE"))
- {
- receive_cr_response(c, &buf);
- }
- else if (buf_string_match_head_str(&buf, "AUTH_PENDING"))
- {
- receive_auth_pending(c, &buf);
- }
- else if (buf_string_match_head_str(&buf, "EXIT"))
- {
- receive_exit_message(c);
- }
- else
- {
- msg(D_PUSH_ERRORS, "WARNING: Received unknown control message:
%s", BSTR(&buf));
+ /* commands on the control channel are seperated by \0x00 bytes.
+ * cmdlen does not include the 0 byte of the string */
+ int cmdlen = (int)strnlen(BSTR(&buf), BLEN(&buf));
+
+ if (cmdlen < BLEN(&buf))
+ {
+ /* include the NUL byte and ensure NUL termination */
+ int cmdlen = (int)strlen(BSTR(&buf)) + 1;
+
+ /* Construct a buffer that only holds the current command and
+ * its closing NUL byte */
+ struct buffer cmdbuf = alloc_buf_gc(cmdlen, &gc);
+ buf_write(&cmdbuf, BPTR(&buf), cmdlen);
+
+ /* check we have only printable characters or null byte in the
+ * command string and no newlines */
+ if (!string_check_buf(&buf, CC_PRINT | CC_NULL, CC_CRLF))
+ {
+ msg(D_PUSH_ERRORS, "WARNING: Received control with invalid
characters: %s",
+ format_hex(BPTR(&buf), BLEN(&buf), 256, &gc));
+ }
+ else
+ {
+ parse_incoming_control_channel_command(c, &cmdbuf);
+ }
+ }
+ else
+ {
+ msg(D_PUSH_ERRORS, "WARNING: Ignoring control channel "
+ "message command without NUL termination");
+ }
+ buf_advance(&buf, cmdlen);
}
}
else
diff --git a/tests/unit_tests/openvpn/test_buffer.c
b/tests/unit_tests/openvpn/test_buffer.c
index fbfb937d1..6b860b4cd 100644
--- a/tests/unit_tests/openvpn/test_buffer.c
+++ b/tests/unit_tests/openvpn/test_buffer.c
@@ -354,6 +354,29 @@ test_character_class(void **state)
assert_string_equal(buf, "There is a .'nice.' \"1234\" [.] year old
.tree!");
}
+
+static void
+test_character_string_mod_buf(void **state)
+{
+ struct gc_arena gc = gc_new();
+
+ struct buffer buf = alloc_buf_gc(1024, &gc);
+
+ const char test1[] = "There is a nice 1234\x00 year old tree!";
+ buf_write(&buf, test1, sizeof(test1));
+
+ /* allow the null bytes and string but not the ! */
+ assert_false(string_check_buf(&buf, CC_ALNUM | CC_SPACE | CC_NULL, 0));
+
+ /* remove final ! and null byte to pass */
+ buf_inc_len(&buf, -2);
+ assert_true(string_check_buf(&buf, CC_ALNUM | CC_SPACE | CC_NULL, 0));
+
+ /* Check excluding digits works */
+ assert_false(string_check_buf(&buf, CC_ALNUM | CC_SPACE | CC_NULL,
CC_DIGIT));
+ gc_free(&gc);
+}
+
static void
test_snprintf(void **state)
{
@@ -437,6 +460,7 @@ main(void)
cmocka_unit_test(test_buffer_free_gc_two),
cmocka_unit_test(test_buffer_gc_realloc),
cmocka_unit_test(test_character_class),
+ cmocka_unit_test(test_character_string_mod_buf),
cmocka_unit_test(test_snprintf)
};
--
2.39.3 (Apple Git-146)
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