[PATCH 1/1] sctp: Protect cached endpoints to prevent possible UAF

[PATCH 1/1] sctp: Protect cached endpoints to prevent possible UAF

[Lee Jones]

The cause of the resultant dump_stack() reported below is a
dereference of a freed pointer to 'struct sctp_endpoint' in
sctp_sock_dump().

This race condition occurs when a transport is cached into its
associated hash table then freed prior to its subsequent use in
sctp_diag_dump() which uses sctp_for_each_transport() to walk the
(now out of date) hash table calling into sctp_sock_dump() where the
dereference occurs.

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.

  BUG: KASAN: use-after-free in sctp_sock_dump+0xa8/0x438 [sctp_diag]
  Call trace:
   dump_backtrace+0x0/0x2dc
   show_stack+0x20/0x2c
   dump_stack+0x120/0x144
   print_address_description+0x80/0x2f4
   __kasan_report+0x174/0x194
   kasan_report+0x10/0x18
   __asan_load8+0x84/0x8c
   sctp_sock_dump+0xa8/0x438 [sctp_diag]
   sctp_for_each_transport+0x1e0/0x26c [sctp]
   sctp_diag_dump+0x180/0x1f0 [sctp_diag]
   inet_diag_dump+0x12c/0x168
   netlink_dump+0x24c/0x5b8
   __netlink_dump_start+0x274/0x2a8
   inet_diag_handler_cmd+0x224/0x274
   sock_diag_rcv_msg+0x21c/0x230
   netlink_rcv_skb+0xe0/0x1bc
   sock_diag_rcv+0x34/0x48
   netlink_unicast+0x3b4/0x430
   netlink_sendmsg+0x4f0/0x574
   sock_write_iter+0x18c/0x1f0
   do_iter_readv_writev+0x230/0x2a8
   do_iter_write+0xc8/0x2b4
   vfs_writev+0xf8/0x184
   do_writev+0xb0/0x1a8
   __arm64_sys_writev+0x4c/0x5c
   el0_svc_common+0x118/0x250
   el0_svc_handler+0x3c/0x9c
   el0_svc+0x8/0xc

Cc: Vlad Yasevich <vyasevich@gmail.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: lksctp developers <linux-sctp@vger.kernel.org>
Cc: "H.P. Yarroll" <piggy@acm.org>
Cc: Karl Knutson <karl@athena.chicago.il.us>
Cc: Jon Grimm <jgrimm@us.ibm.com>
Cc: Xingang Guo <xingang.guo@intel.com>
Cc: Hui Huang <hui.huang@nokia.com>
Cc: Sridhar Samudrala <sri@us.ibm.com>
Cc: Daisy Chang <daisyc@us.ibm.com>
Cc: Ryan Layer <rmlayer@us.ibm.com>
Cc: Kevin Gao <kevin.gao@intel.com>
Cc: linux-sctp@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
---
 net/sctp/associola.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/sctp/associola.c b/net/sctp/associola.c
index be29da09cc7ab..df171a297d095 100644
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -499,8 +499,9 @@ void sctp_assoc_rm_peer(struct sctp_association *asoc,
 
 	/* Remove this peer from the list. */
 	list_del_rcu(&peer->transports);
-	/* Remove this peer from the transport hashtable */
+	/* Remove this peer from the transport hashtable and remove its reference */
 	sctp_unhash_transport(peer);
+	sctp_endpoint_put(asoc->ep);
 
 	/* Get the first transport of asoc. */
 	pos = asoc->peer.transport_addr_list.next;
@@ -710,11 +711,12 @@ struct sctp_transport *sctp_assoc_add_peer(struct sctp_association *asoc,
 	/* Set the peer's active state. */
 	peer->state = peer_state;
 
-	/* Add this peer into the transport hashtable */
+	/* Add this peer into the transport hashtable and take a reference */
 	if (sctp_hash_transport(peer)) {
 		sctp_transport_free(peer);
 		return NULL;
 	}
+	sctp_endpoint_hold(asoc->ep);
 
 	sctp_transport_pl_reset(peer);
 
-- 
2.34.1.400.ga245620fadb-goog

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

[Lee Jones]

On Wed, 08 Dec 2021, Lee Jones wrote:

> The cause of the resultant dump_stack() reported below is a
> dereference of a freed pointer to 'struct sctp_endpoint' in
> sctp_sock_dump().
> 
> This race condition occurs when a transport is cached into its
> associated hash table then freed prior to its subsequent use in
> sctp_diag_dump() which uses sctp_for_each_transport() to walk the
> (now out of date) hash table calling into sctp_sock_dump() where the
> dereference occurs.
> 
> 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.
> 
>   BUG: KASAN: use-after-free in sctp_sock_dump+0xa8/0x438 [sctp_diag]
>   Call trace:
>    dump_backtrace+0x0/0x2dc
>    show_stack+0x20/0x2c
>    dump_stack+0x120/0x144
>    print_address_description+0x80/0x2f4
>    __kasan_report+0x174/0x194
>    kasan_report+0x10/0x18
>    __asan_load8+0x84/0x8c
>    sctp_sock_dump+0xa8/0x438 [sctp_diag]
>    sctp_for_each_transport+0x1e0/0x26c [sctp]
>    sctp_diag_dump+0x180/0x1f0 [sctp_diag]
>    inet_diag_dump+0x12c/0x168
>    netlink_dump+0x24c/0x5b8
>    __netlink_dump_start+0x274/0x2a8
>    inet_diag_handler_cmd+0x224/0x274
>    sock_diag_rcv_msg+0x21c/0x230
>    netlink_rcv_skb+0xe0/0x1bc
>    sock_diag_rcv+0x34/0x48
>    netlink_unicast+0x3b4/0x430
>    netlink_sendmsg+0x4f0/0x574
>    sock_write_iter+0x18c/0x1f0
>    do_iter_readv_writev+0x230/0x2a8
>    do_iter_write+0xc8/0x2b4
>    vfs_writev+0xf8/0x184
>    do_writev+0xb0/0x1a8
>    __arm64_sys_writev+0x4c/0x5c
>    el0_svc_common+0x118/0x250
>    el0_svc_handler+0x3c/0x9c
>    el0_svc+0x8/0xc

This looks related (reported 3 years ago!)

  https://lore.kernel.org/all/20181122131344.GD31918@localhost.localdomain/

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

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

[Marcelo Ricardo Leitner]

On Wed, Dec 08, 2021 at 04:54:34PM +0000, Lee Jones wrote:
> The cause of the resultant dump_stack() reported below is a
> dereference of a freed pointer to 'struct sctp_endpoint' in
> sctp_sock_dump().

Hi,

Please give me another day to review this one.

Thanks,
Marcelo

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

[Marcelo Ricardo Leitner]

On Wed, Dec 08, 2021 at 05:02:12PM +0000, Lee Jones wrote:
> On Wed, 08 Dec 2021, Lee Jones wrote:
> 
> > The cause of the resultant dump_stack() reported below is a
> > dereference of a freed pointer to 'struct sctp_endpoint' in
> > sctp_sock_dump().
> > 
> > This race condition occurs when a transport is cached into its
> > associated hash table then freed prior to its subsequent use in
> > sctp_diag_dump() which uses sctp_for_each_transport() to walk the
> > (now out of date) hash table calling into sctp_sock_dump() where the
> > dereference occurs.
> > 
> > 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.
> > 
> >   BUG: KASAN: use-after-free in sctp_sock_dump+0xa8/0x438 [sctp_diag]
> >   Call trace:
> >    dump_backtrace+0x0/0x2dc
> >    show_stack+0x20/0x2c
> >    dump_stack+0x120/0x144
> >    print_address_description+0x80/0x2f4
> >    __kasan_report+0x174/0x194
> >    kasan_report+0x10/0x18
> >    __asan_load8+0x84/0x8c
> >    sctp_sock_dump+0xa8/0x438 [sctp_diag]
> >    sctp_for_each_transport+0x1e0/0x26c [sctp]
> >    sctp_diag_dump+0x180/0x1f0 [sctp_diag]
> >    inet_diag_dump+0x12c/0x168
> >    netlink_dump+0x24c/0x5b8
> >    __netlink_dump_start+0x274/0x2a8
> >    inet_diag_handler_cmd+0x224/0x274
> >    sock_diag_rcv_msg+0x21c/0x230
> >    netlink_rcv_skb+0xe0/0x1bc
> >    sock_diag_rcv+0x34/0x48
> >    netlink_unicast+0x3b4/0x430
> >    netlink_sendmsg+0x4f0/0x574
> >    sock_write_iter+0x18c/0x1f0
> >    do_iter_readv_writev+0x230/0x2a8
> >    do_iter_write+0xc8/0x2b4
> >    vfs_writev+0xf8/0x184
> >    do_writev+0xb0/0x1a8
> >    __arm64_sys_writev+0x4c/0x5c
> >    el0_svc_common+0x118/0x250
> >    el0_svc_handler+0x3c/0x9c
> >    el0_svc+0x8/0xc
> 
> This looks related (reported 3 years ago!)
> 
>   https://lore.kernel.org/all/20181122131344.GD31918@localhost.localdomain/

Agree, seems related. Thanks for root causing it.

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

[Marcelo Ricardo Leitner]

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

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

[Lee Jones]

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