[openssl-dev] Memory leak in application when we use ECDH

[Mody, Darshan (Darshan)]

Matt,

Even after accounting for the EC_KEY we still observe some leak. The leak started after we started using supporting EC with callback SSL_set_tmp_ecdh_callback().

The core dump shows  the string data of the far-end certificates. I cannot pin point  the code in openssl with this regard.

Thanks
Darshan

-----Original Message-----
From: openssl-dev [mailto:openssl-dev-bounces at openssl.org] On Behalf Of Matt Caswell
Sent: Thursday, March 23, 2017 3:31 PM
To: openssl-dev at openssl.org
Subject: Re: [openssl-dev] Memory leak in application when we use ECDH



On 23/03/17 04:35, Mody, Darshan (Darshan) wrote:
> Matt,
> 
> But openssl does not release the memory when it has duplicated the EC 
> Key which comes from the application

You mean it doesn't free the return value from the callback?
Unfortunately SSL_set_tmp_ecdh_callback() is undocumented so there is no "official" description of the memory management semantics of this function (and like I said it has been removed from later versions of OpenSSL altogether so it is unlikely to ever get documented). However my interpretation of the way the code is written is that this is a deliberate design choice, i.e. it is deliberately left to the the application to mange this memory. Presumably multiple invocations across multiple connections could return the same value so it would be inappropriate for OpenSSL to free it.

Matt



> 
>            /* Duplicate the ECDH structure. */
>             if (ecdhp == NULL) {
>                 SSLerr(SSL_F_SSL3_SEND_SERVER_KEY_EXCHANGE, ERR_R_ECDH_LIB);
>                 goto err;
>             }
>             if (s->cert->ecdh_tmp_auto)
>                 ecdh = ecdhp;
>             else if ((ecdh = EC_KEY_dup(ecdhp)) == NULL) { 
>                 SSLerr(SSL_F_SSL3_SEND_SERVER_KEY_EXCHANGE, ERR_R_ECDH_LIB);
>                 goto err;
>             }
> 
> Thanks
> Darshan
> 
> -----Original Message-----
> From: openssl-dev [mailto:openssl-dev-bounces at openssl.org] On Behalf 
> Of Matt Caswell
> Sent: Tuesday, March 21, 2017 3:28 PM
> To: openssl-dev at openssl.org
> Subject: Re: [openssl-dev] Memory leak in application when we use ECDH
> 
> 
> 
> On 21/03/17 09:46, Matt Caswell wrote:
>>
>> There is a potential leak in this case:
>>
>>             if (s->s3->tmp.ecdh != NULL) {
>>                 SSLerr(SSL_F_SSL3_SEND_SERVER_KEY_EXCHANGE,
>>                        ERR_R_INTERNAL_ERROR);
>>                 goto err;
>>             }
>>
>> But this is a "should not happen" scenario - so there is another bug 
>> if that is happening - and you would see "internal error" messages on 
>> the error stack.
>>
>> Another slight oddity in this code is the double check of ecdhp 
>> against NULL which seems redundant (but otherwise harmless):
>>
>>             if (ecdhp == NULL) {
>>                 al = SSL_AD_HANDSHAKE_FAILURE;
>>                 SSLerr(SSL_F_SSL3_SEND_SERVER_KEY_EXCHANGE,
>>                        SSL_R_MISSING_TMP_ECDH_KEY);
>>                 goto f_err;
>>             }
>>
>>             ...
>>
>>             /* Duplicate the ECDH structure. */
>>             if (ecdhp == NULL) {
>>                 SSLerr(SSL_F_SSL3_SEND_SERVER_KEY_EXCHANGE, ERR_R_ECDH_LIB);
>>                 goto err;
>>             }
> 
> Fix for the above issues (which is unlikely to solve your problem) is here:
> 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_openss
> l_openssl_pull_3003&d=DwICAg&c=BFpWQw8bsuKpl1SgiZH64Q&r=bsEULbVnjelD7I
> nzgsegHBEbtXzaIDagy9EuEhJrKfQ&m=lmOlT993M2YueHJqZT9cKMDBkwGi-yB56pEUuk
> i2qv8&s=pgqizfrjno8szLWBm_ROxbSePFpUYCO4KboURycC0no&e=
> 
> Matt
> 
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