linux-kernel - Re: [PATCH 1/1] sctp: Protect cached endpoints to prevent possible UAF

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Message-ID: <YbIOie1KbasjLAhs@google.com>
Date:   Thu, 9 Dec 2021 14:11:21 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     linux-kernel@...r.kernel.org, Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        lksctp developers <linux-sctp@...r.kernel.org>,
        "H.P. Yarroll" <piggy@....org>,
        Karl Knutson <karl@...ena.chicago.il.us>,
        Jon Grimm <jgrimm@...ibm.com>,
        Xingang Guo <xingang.guo@...el.com>,
        Hui Huang <hui.huang@...ia.com>,
        Sridhar Samudrala <sri@...ibm.com>,
        Daisy Chang <daisyc@...ibm.com>,
        Ryan Layer <rmlayer@...ibm.com>,
        Kevin Gao <kevin.gao@...el.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] sctp: Protect cached endpoints to prevent possible
 UAF

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
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