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Date: Fri, 11 Dec 2015 14:35:32 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc: Vlad Yasevich <vyasevich@...il.com>,
netdev <netdev@...r.kernel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
syzkaller <syzkaller@...glegroups.com>,
linux-sctp@...r.kernel.org, Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>
Subject: Re: use-after-free in sctp_do_sm
On Wed, Dec 9, 2015 at 5:41 PM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> On Wed, Dec 09, 2015 at 01:03:56PM -0200, Marcelo Ricardo Leitner wrote:
>> On Wed, Dec 09, 2015 at 03:41:29PM +0100, Dmitry Vyukov wrote:
>> > On Tue, Dec 8, 2015 at 8:22 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> > > On Tue, Dec 8, 2015 at 6:40 PM, Marcelo Ricardo Leitner
>> > > <marcelo.leitner@...il.com> wrote:
>> ...
>> > >> The patches were combined already, but this last pick by Vlad is just
>> > >> not yet patched. It's not necessary for your testing and I didn't want
>> > >> to interrupt it in case you were already testing it.
>> > >>
>> > >> You can use my last patch here, from 2 emails ago, the one which
>> > >> contains this line:
>> > >> - case SCTP_DISPOSITION_ABORT:
>> > >
>> > >
>> > > You are right. I missed that they are combined. Testing with it now.
>> >
>> >
>> >
>> >
>> > Use-after-free still happens.
>> > I am on commit aa53685549a2cfb5f175b0c4a20bc9aa1e5a1b85 (Dec 8) plus
>> > the following sctp-related changes:
>>
>> Changes are fine. Ugh. Ok, I'll try your new reproducer here.
>
> Heh I wasn't going to reproduce this by myself anytime soon, I think.
> It's using the same socket to connect to itself, and only happens if the
> connect() gets there before the listen() call. Figured this out because
> I could only reproduce it under strace at first.
>
> Please give this other patch a try. A state command
> (sctp_sf_cookie_wait_prm_abort) was issuing SCTP_CMD_INIT_FAILED, which
> leads to SCTP_CMD_DELETE_TCB, but returning SCTP_DISPOSITION_CONSUME,
> which fooled the patch.
>
> ---8<---
> commit 9f84d50e36cee0ce66e4ce9b3b1665e0a1dbcdd3
> Author: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> Date: Fri Dec 4 15:30:23 2015 -0200
>
> sctp: fix use-after-free in pr_debug statement
>
> Dmitry Vyukov reported a use-after-free in the code expanded by the
> macro debug_post_sfx, which is caused by the use of the asoc pointer
> after it was freed within sctp_side_effect() scope.
>
> This patch fixes it by allowing sctp_side_effect to clear that asoc
> pointer when the TCB is freed.
>
> As Vlad explained, we also have to cover the SCTP_DISPOSITION_ABORT case
> because it will trigger DELETE_TCB too on that same loop.
>
> Also, there was a place issuing SCTP_CMD_INIT_FAILED but returning
> SCTP_DISPOSITION_CONSUME, which would fool the scheme above. Fix it by
> returning SCTP_DISPOSITION_ABORT instead.
>
> The macro is already prepared to handle such NULL pointer.
>
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
>
> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> index 6098d4c42fa9..be23d5c2074f 100644
> --- a/net/sctp/sm_sideeffect.c
> +++ b/net/sctp/sm_sideeffect.c
> @@ -63,7 +63,7 @@ static int sctp_cmd_interpreter(sctp_event_t event_type,
> static int sctp_side_effects(sctp_event_t event_type, sctp_subtype_t subtype,
> sctp_state_t state,
> struct sctp_endpoint *ep,
> - struct sctp_association *asoc,
> + struct sctp_association **asoc,
> void *event_arg,
> sctp_disposition_t status,
> sctp_cmd_seq_t *commands,
> @@ -1123,7 +1123,7 @@ int sctp_do_sm(struct net *net, sctp_event_t event_type, sctp_subtype_t subtype,
> debug_post_sfn();
>
> error = sctp_side_effects(event_type, subtype, state,
> - ep, asoc, event_arg, status,
> + ep, &asoc, event_arg, status,
> &commands, gfp);
> debug_post_sfx();
>
> @@ -1136,7 +1136,7 @@ int sctp_do_sm(struct net *net, sctp_event_t event_type, sctp_subtype_t subtype,
> static int sctp_side_effects(sctp_event_t event_type, sctp_subtype_t subtype,
> sctp_state_t state,
> struct sctp_endpoint *ep,
> - struct sctp_association *asoc,
> + struct sctp_association **asoc,
> void *event_arg,
> sctp_disposition_t status,
> sctp_cmd_seq_t *commands,
> @@ -1151,7 +1151,7 @@ static int sctp_side_effects(sctp_event_t event_type, sctp_subtype_t subtype,
> * disposition SCTP_DISPOSITION_CONSUME.
> */
> if (0 != (error = sctp_cmd_interpreter(event_type, subtype, state,
> - ep, asoc,
> + ep, *asoc,
> event_arg, status,
> commands, gfp)))
> goto bail;
> @@ -1174,11 +1174,12 @@ static int sctp_side_effects(sctp_event_t event_type, sctp_subtype_t subtype,
> break;
>
> case SCTP_DISPOSITION_DELETE_TCB:
> + case SCTP_DISPOSITION_ABORT:
> /* This should now be a command. */
> + *asoc = NULL;
> break;
>
> case SCTP_DISPOSITION_CONSUME:
> - case SCTP_DISPOSITION_ABORT:
> /*
> * We should no longer have much work to do here as the
> * real work has been done as explicit commands above.
> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> index 6f46aa16cb76..d801e151498a 100644
> --- a/net/sctp/sm_statefuns.c
> +++ b/net/sctp/sm_statefuns.c
> @@ -4959,12 +4959,10 @@ sctp_disposition_t sctp_sf_cookie_wait_prm_abort(
> sctp_cmd_seq_t *commands)
> {
> struct sctp_chunk *abort = arg;
> - sctp_disposition_t retval;
>
> /* Stop T1-init timer */
> sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_STOP,
> SCTP_TO(SCTP_EVENT_TIMEOUT_T1_INIT));
> - retval = SCTP_DISPOSITION_CONSUME;
>
> sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(abort));
>
> @@ -4983,7 +4981,7 @@ sctp_disposition_t sctp_sf_cookie_wait_prm_abort(
> sctp_add_cmd_sf(commands, SCTP_CMD_INIT_FAILED,
> SCTP_PERR(SCTP_ERROR_USER_ABORT));
>
> - return retval;
> + return SCTP_DISPOSITION_ABORT;
> }
>
> /*
Still happens...
I am on commit aa53685549a2cfb5f175b0c4a20bc9aa1e5a1b85 with your
latest patch applied.
Can you figure out what happens now from the report below? If not I
can create a repro, it's just somewhat time consuming.
BUG: KASAN: use-after-free in sctp_do_sm+0x4bca/0x4db0 at addr ffff880067c600a8
Read of size 4 by task syzkaller_execu/10266
=============================================================================
BUG kmalloc-4096 (Tainted: G W ): kasan: bad access detected
-----------------------------------------------------------------------------
Disabling lock debugging due to kernel taint
INFO: Allocated in sctp_association_new+0x6f/0x1da0 age=53 cpu=2 pid=10265
[< none >] ___slab_alloc+0x489/0x4e0 mm/slub.c:2468
[< none >] __slab_alloc+0x4c/0x90 mm/slub.c:2497
[< inline >] slab_alloc_node mm/slub.c:2560
[< inline >] slab_alloc mm/slub.c:2602
[< none >] kmem_cache_alloc_trace+0x264/0x2f0 mm/slub.c:2619
[< inline >] kmalloc include/linux/slab.h:458
[< inline >] kzalloc include/linux/slab.h:602
[< none >] sctp_association_new+0x6f/0x1da0 net/sctp/associola.c:302
[< none >] sctp_unpack_cookie+0x8b0/0x11c0
net/sctp/sm_make_chunk.c:1812
[< none >] sctp_sf_do_5_1D_ce+0x3ca/0x1410 net/sctp/sm_statefuns.c:702
[< none >] sctp_do_sm+0x20d/0x4db0 net/sctp/sm_sideeffect.c:1122
[< none >] sctp_endpoint_bh_rcv+0x38d/0x830 net/sctp/endpointola.c:486
[< none >] sctp_inq_push+0x12c/0x190 net/sctp/inqueue.c:95
[< none >] sctp_rcv+0x1d3b/0x2840 net/sctp/input.c:270
[< none >] ip_local_deliver_finish+0x2b0/0xa50 net/ipv4/ip_input.c:216
[< inline >] NF_HOOK_THRESH include/linux/netfilter.h:226
[< inline >] NF_HOOK include/linux/netfilter.h:249
[< none >] ip_local_deliver+0x1c4/0x2f0 net/ipv4/ip_input.c:257
[< inline >] dst_input include/net/dst.h:465
[< none >] ip_rcv_finish+0x5ea/0x1730 net/ipv4/ip_input.c:365
[< inline >] NF_HOOK_THRESH include/linux/netfilter.h:226
[< inline >] NF_HOOK include/linux/netfilter.h:249
[< none >] ip_rcv+0x963/0x1080 net/ipv4/ip_input.c:455
[< none >] __netif_receive_skb_core+0x1636/0x2f90 net/core/dev.c:3943
[< none >] __netif_receive_skb+0x2a/0x160 net/core/dev.c:3978
INFO: Freed in sctp_association_put+0x150/0x250 age=0 cpu=2 pid=10266
[< none >] __slab_free+0x1fc/0x320 mm/slub.c:2678
[< inline >] slab_free mm/slub.c:2833
[< none >] kfree+0x26a/0x290 mm/slub.c:3662
[< inline >] sctp_association_destroy net/sctp/associola.c:424
[< none >] sctp_association_put+0x150/0x250 net/sctp/associola.c:860
[< none >] sctp_association_free+0x3dc/0x520 net/sctp/associola.c:402
[< inline >] sctp_cmd_delete_tcb net/sctp/sm_sideeffect.c:867
[< inline >] sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1287
[< inline >] sctp_side_effects net/sctp/sm_sideeffect.c:1153
[< none >] sctp_do_sm+0x175c/0x4db0 net/sctp/sm_sideeffect.c:1125
[< none >] sctp_primitive_ABORT+0xa9/0xd0 net/sctp/primitive.c:119
[< none >] sctp_close+0x274/0x7b0 net/sctp/socket.c:1517
[< none >] inet_release+0xed/0x1c0 net/ipv4/af_inet.c:413
[< none >] sock_release+0x8d/0x1d0 net/socket.c:571
[< none >] sock_close+0x16/0x20 net/socket.c:1022
[< none >] __fput+0x233/0x780 fs/file_table.c:208
[< none >] ____fput+0x15/0x20 fs/file_table.c:244
[< none >] task_work_run+0x16b/0x200 kernel/task_work.c:115
[< inline >] exit_task_work include/linux/task_work.h:21
[< none >] do_exit+0x8bb/0x2b20 kernel/exit.c:750
[< none >] do_group_exit+0x108/0x320 kernel/exit.c:880
[< none >] get_signal+0x5e4/0x1500 kernel/signal.c:2307
INFO: Slab 0xffffea00019f1800 objects=7 used=1 fp=0xffff880067c60000
flags=0x5fffc0000004080
INFO: Object 0xffff880067c60000 @offset=0 fp=0xffff880067c623b0
CPU: 2 PID: 10266 Comm: syzkaller_execu Tainted: G B W
4.4.0-rc4+ #160
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
00000000ffffffff ffff880038777458 ffffffff82899b0d ffff88003e806a00
ffff880067c60000 ffff880067c60000 ffff880038777488 ffffffff816c5564
ffff88003e806a00 ffffea00019f1800 ffff880067c60000 ffff880067c60000
Call Trace:
[< inline >] __dump_stack lib/dump_stack.c:15
[<ffffffff82899b0d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
[<ffffffff816c5564>] print_trailer+0xf4/0x150 mm/slub.c:659
[<ffffffff816cbd1f>] object_err+0x2f/0x40 mm/slub.c:689
[< inline >] print_address_description mm/kasan/report.c:138
[<ffffffff816ce6dd>] kasan_report_error+0x25d/0x560 mm/kasan/report.c:251
[< inline >] kasan_report mm/kasan/report.c:274
[<ffffffff816cea9e>] __asan_report_load4_noabort+0x3e/0x40
mm/kasan/report.c:294
[< inline >] sctp_assoc2id include/net/sctp/sctp.h:323
[<ffffffff8566f14a>] sctp_do_sm+0x4bca/0x4db0 net/sctp/sm_sideeffect.c:1128
[<ffffffff856c6289>] sctp_primitive_ABORT+0xa9/0xd0 net/sctp/primitive.c:119
[<ffffffff856b1d94>] sctp_close+0x274/0x7b0 net/sctp/socket.c:1517
[<ffffffff84f29dcd>] inet_release+0xed/0x1c0 net/ipv4/af_inet.c:413
[<ffffffff84ae520d>] sock_release+0x8d/0x1d0 net/socket.c:571
[<ffffffff84ae5366>] sock_close+0x16/0x20 net/socket.c:1022
[<ffffffff81715f73>] __fput+0x233/0x780 fs/file_table.c:208
[<ffffffff81716545>] ____fput+0x15/0x20 fs/file_table.c:244
[<ffffffff8134679b>] task_work_run+0x16b/0x200 kernel/task_work.c:115
[< inline >] exit_task_work include/linux/task_work.h:21
[<ffffffff812f4d3b>] do_exit+0x8bb/0x2b20 kernel/exit.c:750
[<ffffffff812f7118>] do_group_exit+0x108/0x320 kernel/exit.c:880
[<ffffffff813196c4>] get_signal+0x5e4/0x1500 kernel/signal.c:2307
[<ffffffff811507a3>] do_signal+0x83/0x1c90 arch/x86/kernel/signal.c:712
[<ffffffff81003901>] exit_to_usermode_loop+0xf1/0x1a0
arch/x86/entry/common.c:247
[< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:282
[<ffffffff8100631f>] syscall_return_slowpath+0x19f/0x210
arch/x86/entry/common.c:344
[<ffffffff85b676e2>] int_ret_from_sys_call+0x25/0x9f
arch/x86/entry/entry_64.S:281
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