Crash in mail module during SMTP setup

[Maxim Dounin]

Hello!

On Thu, Aug 01, 2019 at 09:32:20AM +1000, Rob N ★ wrote:

> On Wed, 31 Jul 2019, at 2:11 AM, Maxim Dounin wrote:
> > > I think I see the problem - when using SMTP with SSL and 
> > > resolver, read events might be enabled during address 
> > > resolving, leading to duplicate 
> > > ngx_mail_ssl_handshake_handler() calls if something arrives 
> > > from the client, and duplicate session initialization - 
> > > including starting another resolving.
> 
> That neatly explains why the problem became more noticeable as 
> number of connections went up. With the load a little higher, 
> DNS resolution could conceivable take a little longer, making it 
> more likely that the bug would be triggered.
> 
> > > The following patch should resolve this:
> 
> I've been running the second patch you posted for ~22hrs with no 
> crashes, compared to one every 10-20mins previously. So I think 
> you got it! Thank you so much!

Thanks for testing, committed:

http://hg.nginx.org/nginx/rev/fcd92ad76b7b

-- 
Maxim Dounin
http://mdounin.ru/