netdev - Re: use-after-free in sctp_do

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Date:	Fri, 4 Dec 2015 21:25:35 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Vlad Yasevich <vyasevich@...il.com>,
	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 Fri, Dec 4, 2015 at 6:48 PM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> Hi Dmitry,
>
> Can you please test this patch?
> I'll re-post with proper subject if it works.

Still happening with the same stacks.


> ---8<---
>
> 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.
>
> The macro is already prepared to handle such NULL pointer.
>
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> ---
>  net/sctp/sm_sideeffect.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> index 6098d4c42fa91287d3cde36ac05d860f76d4fe32..05594dcd93e0d649cace5215d225bef2713f9310 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;
> @@ -1175,6 +1175,7 @@ static int sctp_side_effects(sctp_event_t event_type, sctp_subtype_t subtype,
>
>         case SCTP_DISPOSITION_DELETE_TCB:
>                 /* This should now be a command. */
> +               *asoc = NULL;
>                 break;
>
>         case SCTP_DISPOSITION_CONSUME:
> --
> 2.5.0
>
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