On Sun, Jul 28, 2024 at 05:56:33PM +0100, Jeremy Harris via Exim-users wrote:
> > BUT in the log, I get the following message:
> >
> > H=gmail-smtp-in.l.google.com [142.251.16.26] TLS error on
> > connection (recv): The TLS connection was non-properly terminated.
>
> Google is violating standards, according to the OpenSSL library.
No, rather the Google MTA is not wasting valuable resources doing
unnecessary TLS-layer framing to avoid truncation attacks that
don't apply to SMTP, which does application-layer framing.
> Complain to them (and you'll be ignoredr, like the rest of us).
Exim really should be updated to ignore OpenSSL's truncation detection,
I don't recall whether that even already happened and the OP is running
an older version?
All it takes is including `SSL_OP_IGNORE_UNEXPECTED_EOF` in a call
to `SSL_CTX_set_options()`.
For comparison, the associated delta in Postfix below.
--
Viktor.
commit 6876e420275bb44e98827c76306f7ff5481eb192
Author: Wietse Venema <wie...@porcupine.org>
Date: Sat Jan 21 00:00:00 2023 -0500
postfix-3.8-20230121
--- a/postfix/HISTORY
+++ b/postfix/HISTORY
@@ -26779 +26779,10 @@ Apologies for any names omitted.
warning message tls.tls_dh.c.
+
+20230115
+ Workaround for a breaking change in OpenSSL 3: always turn
+ on SSL_OP_IGNORE_UNEXPECTED_EOF, to avoid warning messages
+ and missed opportunities for TLS session reuse. This is
+ safe because the SMTP protocol implements application-level
+ framing, and is therefore not affected by TLS truncation
+ attacks. Fix by Viktor Dukhovni. Files: tls/tls.h, tls_client.c,
+ tls/tls_server.c.
--- a/postfix/src/tls/tls.h
+++ b/postfix/src/tls/tls.h
@@ -389,2 +389,9 @@ extern void tls_param_init(void);
+/*
+ * Always used when defined, SMTP has no truncation attacks.
+ */
+#ifndef SSL_OP_IGNORE_UNEXPECTED_EOF
+#define SSL_OP_IGNORE_UNEXPECTED_EOF 0L
+#endif
+
#define TLS_KNOWN_PROTOCOLS \
@@ -405,3 +412,4 @@ extern void tls_param_init(void);
#define TLS_SSL_OP_MANAGED_BITS \
- (SSL_OP_CIPHER_SERVER_PREFERENCE | TLS_SSL_OP_PROTOMASK(~0))
+ (SSL_OP_CIPHER_SERVER_PREFERENCE | SSL_OP_IGNORE_UNEXPECTED_EOF | \
+ TLS_SSL_OP_PROTOMASK(~0))
--- a/postfix/src/tls/tls_client.c
+++ b/postfix/src/tls/tls_client.c
@@ -715,2 +715,11 @@ TLS_APPL_STATE *tls_client_init(const
TLS_CLIENT_INIT_PROPS *props)
+ /*
+ * Presently we use TLS only with SMTP where truncation attacks are not
+ * possible as a result of application framing. If we ever use TLS in
+ * some other application protocol where truncation could be relevant,
+ * we'd need to disable truncation detection conditionally, or explicitly
+ * clear the option in that code path.
+ */
+ off |= SSL_OP_IGNORE_UNEXPECTED_EOF;
+
/*
diff --git a/postfix/src/tls/tls_server.c b/postfix/src/tls/tls_server.c
index 6caf3ab54..b76cfbc70 100644
--- a/postfix/src/tls/tls_server.c
+++ b/postfix/src/tls/tls_server.c
@@ -514,2 +514,11 @@ TLS_APPL_STATE *tls_server_init(const
TLS_SERVER_INIT_PROPS *props)
+ /*
+ * Presently we use TLS only with SMTP where truncation attacks are not
+ * possible as a result of application framing. If we ever use TLS in
+ * some other application protocol where truncation could be relevant,
+ * we'd need to disable truncation detection conditionally, or explicitly
+ * clear the option in that code path.
+ */
+ off |= SSL_OP_IGNORE_UNEXPECTED_EOF;
+
/*
--
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