[PATCH net] sctp: fix sleep in atomic context bug in timer handlers

[PATCH net] sctp: fix sleep in atomic context bug in timer handlers

[Duoming Zhou]

There are sleep in atomic context bugs in timer handlers of sctp
such as sctp_generate_t3_rtx_event(), sctp_generate_probe_event(),
sctp_generate_t1_init_event(), sctp_generate_timeout_event(),
sctp_generate_t3_rtx_event() and so on.

The root cause is sctp_sched_prio_init_sid() with GFP_KERNEL parameter
that may sleep could be called by different timer handlers which is in
interrupt context.

One of the call paths that could trigger bug is shown below:

      (interrupt context)
sctp_generate_probe_event
  sctp_do_sm
    sctp_side_effects
      sctp_cmd_interpreter
        sctp_outq_teardown
          sctp_outq_init
            sctp_sched_set_sched
              n->init_sid(..,GFP_KERNEL)
                sctp_sched_prio_init_sid //may sleep

This patch changes gfp_t parameter of init_sid in sctp_sched_set_sched()
from GFP_KERNEL to GFP_ATOMIC in order to prevent sleep in atomic
context bugs.

Fixes: 5bbbbe32a431 ("sctp: introduce stream scheduler foundations")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
 net/sctp/stream_sched.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/stream_sched.c b/net/sctp/stream_sched.c
index 518b1b9bf89..1ad565ed562 100644
--- a/net/sctp/stream_sched.c
+++ b/net/sctp/stream_sched.c
@@ -160,7 +160,7 @@ int sctp_sched_set_sched(struct sctp_association *asoc,
 		if (!SCTP_SO(&asoc->stream, i)->ext)
 			continue;
 
-		ret = n->init_sid(&asoc->stream, i, GFP_KERNEL);
+		ret = n->init_sid(&asoc->stream, i, GFP_ATOMIC);
 		if (ret)
 			goto err;
 	}
-- 
2.17.1

Re: [PATCH net] sctp: fix sleep in atomic context bug in timer handlers

[Marcelo Ricardo Leitner]

Hi,

On Sat, Jul 23, 2022 at 09:58:09AM +0800, Duoming Zhou wrote:
> There are sleep in atomic context bugs in timer handlers of sctp
> such as sctp_generate_t3_rtx_event(), sctp_generate_probe_event(),
> sctp_generate_t1_init_event(), sctp_generate_timeout_event(),
> sctp_generate_t3_rtx_event() and so on.
> 
> The root cause is sctp_sched_prio_init_sid() with GFP_KERNEL parameter
> that may sleep could be called by different timer handlers which is in
> interrupt context.
> 
> One of the call paths that could trigger bug is shown below:
> 
>       (interrupt context)
> sctp_generate_probe_event
>   sctp_do_sm
>     sctp_side_effects
>       sctp_cmd_interpreter
>         sctp_outq_teardown
>           sctp_outq_init

This sequence is odd but it is used when handling dup cookies. It
tears down whatever was in there and re-inits it. With that,

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

>             sctp_sched_set_sched
>               n->init_sid(..,GFP_KERNEL)
>                 sctp_sched_prio_init_sid //may sleep

Re: [PATCH net] sctp: fix sleep in atomic context bug in timer handlers

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Sat, 23 Jul 2022 09:58:09 +0800 you wrote:
> There are sleep in atomic context bugs in timer handlers of sctp
> such as sctp_generate_t3_rtx_event(), sctp_generate_probe_event(),
> sctp_generate_t1_init_event(), sctp_generate_timeout_event(),
> sctp_generate_t3_rtx_event() and so on.
> 
> The root cause is sctp_sched_prio_init_sid() with GFP_KERNEL parameter
> that may sleep could be called by different timer handlers which is in
> interrupt context.
> 
> [...]

Here is the summary with links:
  - [net] sctp: fix sleep in atomic context bug in timer handlers
    https://git.kernel.org/netdev/net/c/b89fc26f741d

You are awesome, thank you!
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