Date:   Thu, 9 Dec 2021 14:11:21 +0000
From:   Lee Jones <lee.jones@linaro.org>
To:     Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc:     linux-kernel@vger.kernel.org, Vlad Yasevich <vyasevich@gmail.com>,
        Neil Horman <nhorman@tuxdriver.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        lksctp developers <linux-sctp@vger.kernel.org>,
        "H.P. Yarroll" <piggy@acm.org>,
        Karl Knutson <karl@athena.chicago.il.us>,
        Jon Grimm <jgrimm@us.ibm.com>,
        Xingang Guo <xingang.guo@intel.com>,
        Hui Huang <hui.huang@nokia.com>,
        Sridhar Samudrala <sri@us.ibm.com>,
        Daisy Chang <daisyc@us.ibm.com>,
        Ryan Layer <rmlayer@us.ibm.com>,
        Kevin Gao <kevin.gao@intel.com>, netdev@vger.kernel.org
Subject: Re: [PATCH 1/1] sctp: Protect cached endpoints to prevent possible
 UAF
Message-ID: <YbIOie1KbasjLAhs@google.com>
References: <20211208165434.2962062-1-lee.jones@linaro.org>
 <YbH5um3HVQbSecx4@t14s.localdomain>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <YbH5um3HVQbSecx4@t14s.localdomain>
Precedence: bulk

On Thu, 09 Dec 2021, Marcelo Ricardo Leitner wrote:

> On Wed, Dec 08, 2021 at 04:54:34PM +0000, Lee Jones wrote:
> > To prevent this from happening we need to take a reference on the
> > to-be-used/dereferenced 'struct sctp_endpoint' until such a time when
> > we know it can be safely released.
> > 
> > When KASAN is not enabled, a similar, but slightly different NULL
> > pointer derefernce crash occurs later along the thread of execution in
> > inet_sctp_diag_fill() this time.
> 
> Hey Lee, did you try running lksctp-tools [1] func tests with this patch?
> I'm getting failures here.
> 
> [root@vm1 func_tests]# make v4test
> ./test_assoc_abort
> test_assoc_abort.c  1 PASS : ABORT an association using SCTP_ABORT
> test_assoc_abort passes
> 
> ./test_assoc_shutdown
> test_assoc_shutdown.c  1 BROK : bind: Address already in use
> DUMP_CORE ../../src/testlib/sctputil.h: 145
> /bin/sh: line 1:  3727 Segmentation fault      (core dumped) ./$a
> test_assoc_shutdown fails
> make: *** [Makefile:1648: v4test] Error 1
> 
> I didn't check it closely but it would seem that the ep is beind held
> forever. If I simply retry after a few seconds, it's still there (now the 1st
> test fails):
> 
> [root@vm1 func_tests]# make v4test
> ./test_assoc_abort
> test_assoc_abort.c  1 BROK : bind: Address already in use
> DUMP_CORE ../../src/testlib/sctputil.h: 145
> /bin/sh: line 1:  3751 Segmentation fault      (core dumped) ./$a
> test_assoc_abort fails
> 
> 1.https://github.com/sctp/lksctp-tools

No I haven't, but I will do once I get a moment.

The only thing I can think of, before I go digging again, is that
either the association is never unhashed (so it stays in cache
forever - I doubt this, as it would be very bad) or the association
was migrated via sctp_assoc_migrate() and the additional reference was
not transferred across.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog