linux-kernel - Re: [PATCH] net: tls: fix possible race condition between do_tls_getsockopt_conf() and do_tls_setsockopt

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Date:   Fri, 24 Feb 2023 22:48:57 +0100
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Hangyu Hua <hbh25y@...il.com>, Florian Westphal <fw@...len.de>,
        borisp@...dia.com, john.fastabend@...il.com, davem@...emloft.net,
        edumazet@...gle.com, pabeni@...hat.com, davejwatson@...com,
        aviadye@...lanox.com, ilyal@...lanox.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: tls: fix possible race condition between
 do_tls_getsockopt_conf() and do_tls_setsockopt_conf()

2023-02-24, 13:06:25 -0800, Jakub Kicinski wrote:
> On Fri, 24 Feb 2023 21:22:43 +0100 Sabrina Dubroca wrote:
> > > Right, the bug and the fix seem completely bogus.
> > > Please make sure the bugs are real and the fixes you sent actually 
> > > fix them.  
> > 
> > I suggested a change of locking in do_tls_getsockopt_conf this
> > morning [1]. The issue reported last seemed valid, but this patch is not
> > at all what I had in mind.
> > [1] https://lore.kernel.org/all/Y/ht6gQL+u6fj3dG@hog/
> 
> Ack, I read the messages out of order, sorry.
> 
> > do_tls_setsockopt_conf fills crypto_info immediately from what
> > userspace gives us (and clears it on exit in case of failure), which
> > getsockopt could see since it's not locking the socket when it checks
> > TLS_CRYPTO_INFO_READY. So getsockopt would progress up to the point it
> > finally locks the socket, but if setsockopt failed, we could have
> > cleared TLS_CRYPTO_INFO_READY and freed iv/rec_seq.
> 
> Makes sense. We should just take the socket lock around all of
> do_tls_getsockopt(), then? 

That would make things simple and consistent. My idea was just taking
the existing lock_sock in do_tls_getsockopt_conf out of the switch and
put it just above TLS_CRYPTO_INFO_READY.

While we're at it, should we move the

    ctx->prot_info.version != TLS_1_3_VERSION

check in do_tls_setsockopt_no_pad under lock_sock?  I don't think that
can do anything wrong (we'd have to get past this check just before a
failing setsockopt clears crypto_info, and even then we're just
reading a bit from the context), it just looks a bit strange. Or just
lock the socket around all of do_tls_setsockopt_no_pad, like the other
options we have.

-- 
Sabrina