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:

quoted

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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