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Date: Mon, 7 Dec 2015 17:50:32 -0200
From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To: Vlad Yasevich <vyasevich@...il.com>
Cc: Dmitry Vyukov <dvyukov@...gle.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 Mon, Dec 07, 2015 at 02:33:52PM -0500, Vlad Yasevich wrote:
> On 12/07/2015 01:52 PM, Marcelo Ricardo Leitner wrote:
> > On Mon, Dec 07, 2015 at 02:20:47PM +0100, Dmitry Vyukov wrote:
> >> On Mon, Dec 7, 2015 at 2:15 PM, Marcelo Ricardo Leitner
> >> <marcelo.leitner@...il.com> wrote:
> >>> On Mon, Dec 07, 2015 at 12:26:09PM +0100, Dmitry Vyukov wrote:
> >>>> On Sat, Dec 5, 2015 at 5:39 PM, Vlad Yasevich <vyasevich@...il.com> wrote:
> > ...
> >>>>> Hi Marcelo
> >>>>>
> >>>>> I think you also need to catch the SCTP_DISPOSITION_ABORT and update
> >>>>> the pointer. There are some issues there though as some functions report
> >>>>> that code without actually destroying the association. This happens when
> >>>>> the ABORT chunk may be dropped.
> >>>>>
> >>>>> I think this might be why we still see the issue.
> >>>>
> >>>>
> >>>> Marcelo,
> >>>>
> >>>> Is this info enough for you to cook another fix?
> >>>
> >>> Hi, I think so. I was really wondering how you could trigger that issue
> >>> without the timestamp fix and Vlad's comment does shed some light on it.
> >>>
> >>> I'll do more tests later today, but what did you have connecting to the
> >>> listening socket? Somehow you made that accept() call to return..
> >>
> >> Local connect in another thread I guess.
> >
> > Vlad, I reviewed the places on which it returns SCTP_DISPOSITION_ABORT,
> > and if I didn't miss something in there all of them either issue
> > SCTP_CMD_ASSOC_FAILED or SCTP_CMD_INIT_FAILED before returning it, thus
> > delaying DELETE_TCB and with that the asoc free.
>
> They delay it from the perspective of the command interpreter since the command
> to delete the TCB happens a little later, but status code is checked after all
> commands are processed and command processing doesn't change it. So the 'status'
> code would still be SCTP_DISPOSITION_ABORT after DELETE_TCB command was processed.
> So, I think we may still have an use-after-free issue here.
Gotcha! That's pretty much it then. From that point of view now, there
shouldn't be a case that it returns _ABORT without freeing the asoc in
the same loop. (more below)
> > There is one place,
> > though, that may not do it that way, it's sctp_sf_abort_violation(), but
> > then that code only runs if asoc is already NULL by then.
>
> I don't believe so. The violation state function can run with a non-NULL association
> if we are encountering protocol violations after the association is established.
Yup, that's correct. I just tried to reference one case on which it
would return _ABORT without issuing any of those _FAILEDs before doing
so (meaning the association could still be valid) but that in that case,
the asoc was already NULL.
Dmitry, please give this one a run, as I still cannot reproduce your use
case..
---8<---
commit b63ad8dc45257dd6c536ac0227fcc623efd9328b
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.
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.
--
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