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

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Date:   Thu, 9 Dec 2021 09:42:34 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Lee Jones <lee.jones@...aro.org>
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 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

  Marcelo