Re: A new workaround for bug 3816: ssl_crtd crash with OpenSSL v...

On 05/09/2013 05:50 PM, Alex Rousskov wrote:
> Hello,
>
> According to the squid-user exchange below, OpenSSL v0.9.8y is also
> vulnerable. However, it is possible that the stock v0.9.8y is not
> vulnerable, but FreeBSD patched it to make it vulnerable, I guess.

Nope, this is not FreeBSD problem.
This openSSL release has this bug too..

> Christos, can you reproduce the crash with stock v0.9.8y on Linux (if
> you do not have FreeBSD)?

Yep.

>
> I wonder if we should change strategy from compile-time OpenSSL version
> checks to something like this:
>
> // Temporary ssl for getting X509 certificate from SSL_CTX.
> Ssl::SSL_Pointer ssl(SSL_new(sslContext));
> // Various OpenSSL versions crash on a SSL_get_certificate() call:
> // http://bugs.squid-cache.org/show_bug.cgi?id=3816#c16
> // so we avoid that call by extracting certificate directly:
> X509 *cert = ssl->cert ? ssl->cert->key->x509 : NULL;
> if (!cert)
> return false;

The ssl->cert is of type CERT ("struct cert_st") and it is defined in a
header file which is not available to the public openSSL SDK...
So the above (ssl->cert->key->x509) can not be used unless we copy the
"struct cert_st" definition inside squid...
This is why I used the following to get the X509 object:
   X509 ***pCert = (X509 ***)sslContext->cert;

>
> If the "ssl->cert->key->x509" expression is not portable across OpenSSL
> versions, perhaps we can detect that at ./configure time and add an
> #ifdef guard for _that_ (as opposed to OpenSSL version guards)?

I can reporoduce the bug with the following simple program:

int main(int argc, char *argv[])
{
    SSLeay_add_ssl_algorithms();
    SSL_CTX *sslContext = SSL_CTX_new(SSLv3_method());
    SSL *ssl = SSL_new(sslContext);
    X509 * cert = SSL_get_certificate(ssl);
    return 0;
}

This program crashes inside a function called by SSL_get_certificate.
I suppose we can check if the program exited normally or not, to decide
if the openSSL SDK is OK or have the bug.

>
>
> Thank you,
>
> Alex.
>
>
> On 05/09/2013 08:19 AM, Guy Helmer wrote:
>>
>> On May 8, 2013, at 10:55 PM, Alex Rousskov <rousskov_at_measurement-factory.com> wrote:
>>
>>> On 05/08/2013 04:31 PM, Guy Helmer wrote:
>>>
>>>> I was using squid 3.3.4 on FreeBSD 8.3 with transparent interception
>>>> (via ipfw) and ssl bump with success.
>>>
>>>> After upgrading FreeBSD to 9.1 [...] squid is failing with
>>>> segmentation violations and the ssl_crtd helpers are dying.
>>>
>>>> #7 0xbfbff044 in ?? ()
>>>> #8 0x0000000b in ?? ()
>>>> #9 0x484eb5c8 in ssl_get_server_send_pkey () from /usr/lib/libssl.so.6
>>>> #10 0x484eb68d in ssl_get_server_send_cert () from /usr/lib/libssl.so.6
>>>> #11 0x484eb6c4 in SSL_get_certificate () from /usr/lib/libssl.so.6
>>>> #12 0x083cb5ef in Ssl::verifySslCertificate (sslContext=0x4a259340,
>>>> properties=@0xbfbfd9d8) at support.cc:1422
>>>> #13 0x0813d20d in ConnStateData::getSslContextStart (this=0x4a257cd0)
>>>> at client_side.cc:3820
>>>> #14 0x0814a89e in ConnStateData::httpsPeeked (this=0x4a257cd0,
>>>> serverConnection=@0xbfbfdadc) at client_side.cc:3968
>>>
>>> Smells like an OpenSSL bug that we thought we had a workaround for:
>>> http://bugs.squid-cache.org/show_bug.cgi?id=3816
>>>
>>> The workaround should be in v3.3.4 that you are running but, apparently,
>>> it is not sufficient, or our OpenSSL version detection code is failing
>>> in your environment. We thought the bug affects OpenSSL versions 1.0.1d
>>> and 1.0.1e only.
>>>
>>> Which OpenSSL version are you building Squid with?
>>>
>>> What is the OPENSSL_VERSION_NUMBER constant in OpenSSL header files
>>> where you build Squid? You can probably run something like "fgrep -RI
>>> OPENSSL_VERSION_NUMBER /usr/include/openssl" to figure that out.
>>>
>>> Which OpenSSL version are you running Squid with?
>>
>> Under FreeBSD 8.3, it was built and running with OpenSSL 0.9.8q (OPENSSL_VERSION_NUMBER 0x0090811f).
>>
>> Under FreeBSD 9.1 (stable branch checkout as of 2013-04-10), it is built and running with OpenSSL 0.9.8y (OPENSSL_VERSION_NUMBER 0x0090819fL).
>>
>> I made this little change to support.cc, rebuilt squid and ssl_crtd, and it seems to be working OK with transparent SSL bumping:
>>
>> --- src/ssl/support.cc.orig 2013-05-09 08:59:19.000000000 -0500
>> +++ src/ssl/support.cc 2013-05-09 09:00:25.000000000 -0500
>> @@ -1413,7 +1413,7 @@
>> {
>> // SSL_get_certificate is buggy in openssl versions 1.0.1d and 1.0.1e
>> // Try to retrieve certificate directly from SSL_CTX object
>> -#if OPENSSL_VERSION_NUMBER == 0x1000105fL || OPENSSL_VERSION_NUMBER == 0x1000104fL
>> +#if OPENSSL_VERSION_NUMBER == 0x1000105fL || OPENSSL_VERSION_NUMBER == 0x1000104fL || OPENSSL_VERSION_NUMBER == 0x0090819fL
>> X509 ***pCert = (X509 ***)sslContext->cert;
>> X509 * cert = pCert && *pCert ? **pCert : NULL;
>> #else
>>
>> Thanks for the pointer, Alex!
>>
>> Guy
>>
>
>
Received on Thu May 09 2013 - 19:11:09 MDT