* Re: Builtin GnuTLS support and certificate verification
[not found] ` <87y53v7n44.fsf@guybrush.luffy.cx>
@ 2013-12-08 16:08 ` Ted Zlatanov
2013-12-14 18:06 ` Ted Zlatanov
0 siblings, 1 reply; 2+ messages in thread
From: Ted Zlatanov @ 2013-12-08 16:08 UTC (permalink / raw)
To: ding; +Cc: emacs-devel
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On Sun, 08 Dec 2013 09:39:23 +0100 Vincent Bernat <bernat@luffy.cx> wrote:
VB> ❦ 8 décembre 2013 05:22 CET, Ted Zlatanov <tzz@lifelogs.com> :
>>>> Verification options could be:
>>>>
>>>> - `expired-certificate`
>>>> - `revoked-certificate`
>>>> - `untrusted-certificate`
>>>> - `hostname-mismatch`
>>
>> I'm not sure this granularity is necessary. I just have :trustfiles and
>> :hostname as options right now. Anyone else with an opinion?
VB> I thought you wanted something granular, hence the proposition. I don't
VB> know of any other software proposing granular verification. So, no
VB> problem with dropping this.
Yeah, I went back and forth. I think two (:trustfiles and :hostname)
verification options is the right balance for now. I couldn't think of
any cases where I'd want more granularity, but that's why I'm asking :)
>> My concern is that suddenly connections will start failing for our users
>> and bug reports will flow, and I don't have time to explain to everyone
>> why their self-signed certificates need exceptions. This can be really,
>> really annoying. But logging in *Messages* is not very useful either,
>> users don't read it. So what's the right thing? How about a default
>> behavior of flashing a warning, then sit-for 3 seconds? A hard error
>> can be optional but not the default.
VB> For a first release, just default to the previous behaviour. However,
VB> some day, it would be nice to be "secure by default".
http://debbugs.gnu.org/13374 and other related bugs are about enabling
"secure by default" and I would like to make that change now, before the
Emacs code freeze.
It feels like the sit-for option is safest. It preserves the current
behavior while forcing the user to notice something's wrong. In the
next release, based on user feedback, we can turn verify-error on. If
no one disagrees, I will implement it on top of the patch attached here.
>> I'm also not sure I like the look and feel of the `gnutls-verify-error'
>> defcustom. It's kind of awkward.
VB> I am don't know defcustom enough to know if this would give something
VB> like this:
VB> '((".*\\.internal" :hostname)
VB> (".*" :trustfiles :hostname))
VB> If yes, this seems fine for me. Just add the possible values for tags in
VB> the document string.
Yes, except the cdr is a nested list because I use the "set"
customization type. So it's '((".*" (:hostname :trustfiles)))
>> I'd like to get this done before the Emacs code freeze next week or so.
>> Please give me your opinions and test the code.
VB> I'll try to test later this day.
Thanks. Posting patch to emacs-devel as well for review and feedback.
Ted
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=== modified file 'lisp/net/gnutls.el'
--- lisp/net/gnutls.el 2013-09-18 04:50:54 +0000
+++ lisp/net/gnutls.el 2013-12-08 04:00:04 +0000
@@ -51,6 +51,19 @@
:type '(choice (const nil)
string))
+(defcustom gnutls-verify-error nil
+ "If non-nil, this should be a list of checks per hostname regex or t."
+ :group 'gnutls
+ :type '(choice
+ (const t)
+ (repeat :tag "List of hostname regexps with flags for each"
+ (list
+ (choice :tag "Hostname"
+ (const ".*" :tag "Any hostname")
+ regexp)
+ (set (const :trustfiles)
+ (const :hostname))))))
+
(defcustom gnutls-trustfiles
'(
"/etc/ssl/certs/ca-certificates.crt" ; Debian, Ubuntu, Gentoo and Arch Linux
@@ -138,19 +151,25 @@
\(see `gnutls-min-prime-bits' for more information). Use nil for the
default.
-When VERIFY-HOSTNAME-ERROR is not nil, an error will be raised
-when the hostname does not match the presented certificate's host
-name. The exact verification algorithm is a basic implementation
-of the matching described in RFC2818 (HTTPS), which takes into
-account wildcards, and the DNSName/IPAddress subject alternative
-name PKIX extension. See GnuTLS' gnutls_x509_crt_check_hostname
-for details. When VERIFY-HOSTNAME-ERROR is nil, only a warning
-will be issued.
-
-When VERIFY-ERROR is not nil, an error will be raised when the
-peer certificate verification fails as per GnuTLS'
-gnutls_certificate_verify_peers2. Otherwise, only warnings will
-be shown about the verification failure.
+VERIFY-HOSTNAME-ERROR is a backwards compatibility option for
+putting `:hostname' in VERIFY-ERROR.
+
+When VERIFY-ERROR is t or a list containing `:trustfiles', an
+error will be raised when the peer certificate verification fails
+as per GnuTLS' gnutls_certificate_verify_peers2. Otherwise, only
+warnings will be shown about the verification failure.
+
+When VERIFY-ERROR is t or a list containing `:hostname', an error
+will be raised when the hostname does not match the presented
+certificate's host name. The exact verification algorithm is a
+basic implementation of the matching described in
+RFC2818 (HTTPS), which takes into account wildcards, and the
+DNSName/IPAddress subject alternative name PKIX extension. See
+GnuTLS' gnutls_x509_crt_check_hostname for details. Otherwise,
+only a warning will be issued.
+
+Note that the list in `gnutls-verify-error', matched against the
+HOSTNAME, is the default VERIFY-ERROR.
VERIFY-FLAGS is a numeric OR of verification flags only for
`gnutls-x509pki' connections. See GnuTLS' x509.h for details;
@@ -183,8 +202,28 @@
(if gnutls-algorithm-priority
(upcase gnutls-algorithm-priority)
"NORMAL")))))
+ (verify-error (or verify-error
+ ;; this uses the value of `gnutls-verify-error'
+ (cond
+ ;; if t, pass it on
+ ((eq gnutls-verify-error t)
+ t)
+ ;; if a list, look for hostname matches
+ ((listp gnutls-verify-error)
+ (mapcan
+ (lambda (check)
+ (when (string-match (car check) hostname)
+ (cdr check)))
+ gnutls-verify-error))
+ ;; else it's nil
+ (t nil))))
(min-prime-bits (or min-prime-bits gnutls-min-prime-bits))
- (params `(:priority ,priority-string
+ params ret)
+
+ (when verify-hostname-error
+ (push :hostname verify-error))
+
+ (setq params `(:priority ,priority-string
:hostname ,hostname
:loglevel ,gnutls-log-level
:min-prime-bits ,min-prime-bits
@@ -193,9 +232,7 @@
:keylist ,keylist
:verify-flags ,verify-flags
:verify-error ,verify-error
- :verify-hostname-error ,verify-hostname-error
:callbacks nil))
- ret)
(gnutls-message-maybe
(setq ret (gnutls-boot process type params))
=== modified file 'src/gnutls.c'
--- src/gnutls.c 2013-11-30 13:31:39 +0000
+++ src/gnutls.c 2013-12-08 04:10:44 +0000
@@ -49,7 +49,7 @@
static Lisp_Object QCgnutls_bootprop_hostname;
static Lisp_Object QCgnutls_bootprop_min_prime_bits;
static Lisp_Object QCgnutls_bootprop_verify_flags;
-static Lisp_Object QCgnutls_bootprop_verify_hostname_error;
+static Lisp_Object QCgnutls_bootprop_verify_error;
/* Callback keys for `gnutls-boot'. Unused currently. */
static Lisp_Object QCgnutls_bootprop_callbacks_verify;
@@ -753,8 +753,12 @@
:verify-flags is a bitset as per GnuTLS'
gnutls_certificate_set_verify_flags.
-:verify-hostname-error, if non-nil, makes a hostname mismatch an
-error. Otherwise it will be just a warning.
+:verify-hostname-error is ignored. Pass :hostname in :verify-error
+instead.
+
+:verify-error is a list of symbols to express verification checks or
+`t' to do all checks. Currently it can contain `:trustfiles' and
+`:hostname' to verify the certificate or the hostname respectively.
:min-prime-bits is the minimum accepted number of bits the client will
accept in Diffie-Hellman key exchange.
@@ -798,8 +802,7 @@
/* Lisp_Object callbacks; */
Lisp_Object loglevel;
Lisp_Object hostname;
- /* Lisp_Object verify_error; */
- Lisp_Object verify_hostname_error;
+ Lisp_Object verify_error;
Lisp_Object prime_bits;
CHECK_PROCESS (proc);
@@ -818,11 +821,14 @@
keylist = Fplist_get (proplist, QCgnutls_bootprop_keylist);
crlfiles = Fplist_get (proplist, QCgnutls_bootprop_crlfiles);
loglevel = Fplist_get (proplist, QCgnutls_bootprop_loglevel);
- verify_hostname_error = Fplist_get (proplist, QCgnutls_bootprop_verify_hostname_error);
+ verify_error = Fplist_get (proplist, QCgnutls_bootprop_verify_error);
prime_bits = Fplist_get (proplist, QCgnutls_bootprop_min_prime_bits);
+ if (!Flistp (verify_error))
+ error ("gnutls-boot: invalid :verify_error parameter (not a list)");
+
if (!STRINGP (hostname))
- error ("gnutls-boot: invalid :hostname parameter");
+ error ("gnutls-boot: invalid :hostname parameter (not a string)");
c_hostname = SSDATA (hostname);
state = XPROCESS (proc)->gnutls_state;
@@ -1047,14 +1053,17 @@
if (peer_verification != 0)
{
- if (NILP (verify_hostname_error))
- GNUTLS_LOG2 (1, max_log_level, "certificate validation failed:",
- c_hostname);
- else
- {
+ if (EQ (verify_error, Qt)
+ || !NILP (Fmember (QCgnutls_bootprop_trustfiles, verify_error)))
+ {
emacs_gnutls_deinit (proc);
error ("Certificate validation failed %s, verification code %d",
c_hostname, peer_verification);
+ }
+ else
+ {
+ GNUTLS_LOG2 (1, max_log_level, "certificate validation failed:",
+ c_hostname);
}
}
@@ -1094,14 +1103,17 @@
if (!fn_gnutls_x509_crt_check_hostname (gnutls_verify_cert, c_hostname))
{
- if (NILP (verify_hostname_error))
- GNUTLS_LOG2 (1, max_log_level, "x509 certificate does not match:",
- c_hostname);
- else
- {
+ if (EQ (verify_error, Qt)
+ || !NILP (Fmember (QCgnutls_bootprop_hostname, verify_error)))
+ {
fn_gnutls_x509_crt_deinit (gnutls_verify_cert);
emacs_gnutls_deinit (proc);
error ("The x509 certificate does not match \"%s\"", c_hostname);
+ }
+ else
+ {
+ GNUTLS_LOG2 (1, max_log_level, "x509 certificate does not match:",
+ c_hostname);
}
}
fn_gnutls_x509_crt_deinit (gnutls_verify_cert);
@@ -1161,7 +1173,7 @@
DEFSYM (QCgnutls_bootprop_min_prime_bits, ":min-prime-bits");
DEFSYM (QCgnutls_bootprop_loglevel, ":loglevel");
DEFSYM (QCgnutls_bootprop_verify_flags, ":verify-flags");
- DEFSYM (QCgnutls_bootprop_verify_hostname_error, ":verify-hostname-error");
+ DEFSYM (QCgnutls_bootprop_verify_error, ":verify-error");
DEFSYM (Qgnutls_e_interrupted, "gnutls-e-interrupted");
Fput (Qgnutls_e_interrupted, Qgnutls_code,
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