Re: [PATCH net] sctp: fix memory leak in sctp_stream_outq_migrate()

[Xin Long <lucien.xin@gmail.com>]

On Fri, Nov 18, 2022 at 3:48 AM Zhengchao Shao <shaozhengchao@huawei.com> wrote:
>
> When sctp_stream_outq_migrate() is called to release stream out resources,
> the memory pointed to by prio_head in stream out is not released.
>
> The memory leak information is as follows:
> unreferenced object 0xffff88801fe79f80 (size 64):
>   comm "sctp_repo", pid 7957, jiffies 4294951704 (age 36.480s)
>   hex dump (first 32 bytes):
>     80 9f e7 1f 80 88 ff ff 80 9f e7 1f 80 88 ff ff  ................
>     90 9f e7 1f 80 88 ff ff 90 9f e7 1f 80 88 ff ff  ................
>   backtrace:
>     [<ffffffff81b215c6>] kmalloc_trace+0x26/0x60
>     [<ffffffff88ae517c>] sctp_sched_prio_set+0x4cc/0x770
>     [<ffffffff88ad64f2>] sctp_stream_init_ext+0xd2/0x1b0
>     [<ffffffff88aa2604>] sctp_sendmsg_to_asoc+0x1614/0x1a30
>     [<ffffffff88ab7ff1>] sctp_sendmsg+0xda1/0x1ef0
>     [<ffffffff87f765ed>] inet_sendmsg+0x9d/0xe0
>     [<ffffffff8754b5b3>] sock_sendmsg+0xd3/0x120
>     [<ffffffff8755446a>] __sys_sendto+0x23a/0x340
>     [<ffffffff87554651>] __x64_sys_sendto+0xe1/0x1b0
>     [<ffffffff89978b49>] do_syscall_64+0x39/0xb0
>     [<ffffffff89a0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> Fixes: 637784ade221 ("sctp: introduce priority based stream scheduler")
> Reported-by: syzbot+29c402e56c4760763cc0@syzkaller.appspotmail.com
> Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
> ---
>  net/sctp/stream.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/net/sctp/stream.c b/net/sctp/stream.c
> index ef9fceadef8d..a17dc368876f 100644
> --- a/net/sctp/stream.c
> +++ b/net/sctp/stream.c
> @@ -70,6 +70,9 @@ static void sctp_stream_outq_migrate(struct sctp_stream *stream,
>                  * sctp_stream_update will swap ->out pointers.
>                  */
>                 for (i = 0; i < outcnt; i++) {
> +                       if (SCTP_SO(new, i)->ext)
> +                               kfree(SCTP_SO(new, i)->ext->prio_head);
> +
>                         kfree(SCTP_SO(new, i)->ext);
>                         SCTP_SO(new, i)->ext = SCTP_SO(stream, i)->ext;
>                         SCTP_SO(stream, i)->ext = NULL;
> @@ -77,6 +80,9 @@ static void sctp_stream_outq_migrate(struct sctp_stream *stream,
>         }
>
>         for (i = outcnt; i < stream->outcnt; i++) {
> +               if (SCTP_SO(stream, i)->ext)
> +                       kfree(SCTP_SO(stream, i)->ext->prio_head);
> +
>                 kfree(SCTP_SO(stream, i)->ext);
>                 SCTP_SO(stream, i)->ext = NULL;
>         }
> --
> 2.17.1
>
This is not a proper fix:
1. you shouldn't access "prio_head" outside stream_sched_prio.c.
2. the prio_head you freed might be used by other out streams, freeing
it unconditionally would cause either a double free or use after free.

I'm afraid we have to add a ".free_sid" in sctp_sched_ops, and
implement it for sctp_sched_prio, like:

+static void sctp_sched_prio_free_sid(struct sctp_stream *stream, __u16 sid)
+{
+       struct sctp_stream_priorities *prio = SCTP_SO(stream,
sid)->ext->prio_head;
+       int i;
+
+       if (!prio)
+               return;
+
+       SCTP_SO(stream, sid)->ext->prio_head = NULL;
+       for (i = 0; i < stream->outcnt; i++) {
+               if (SCTP_SO(stream, i)->ext &&
+                   SCTP_SO(stream, i)->ext->prio_head == prio)
+                       return;
+       }
+       kfree(prio);
+}
+
 static void sctp_sched_prio_free(struct sctp_stream *stream)
 {
        struct sctp_stream_priorities *prio, *n;
@@ -323,6 +340,7 @@ static struct sctp_sched_ops sctp_sched_prio = {
        .get = sctp_sched_prio_get,
        .init = sctp_sched_prio_init,
        .init_sid = sctp_sched_prio_init_sid,
+       .free_sid = sctp_sched_prio_free_sid,
        .free = sctp_sched_prio_free,
        .enqueue = sctp_sched_prio_enqueue,
        .dequeue = sctp_sched_prio_dequeue,

then call it in sctp_stream_outq_migrate(), like:

+static void sctp_stream_free_ext(struct sctp_stream *stream, __u16 sid)
+{
+       struct sctp_sched_ops *sched = sctp_sched_ops_from_stream(stream);
+
+       sched->free_sid(stream, sid);
+       kfree(SCTP_SO(stream, sid)->ext);
+       SCTP_SO(stream, sid)->ext = NULL;
+}
+
 /* Migrates chunks from stream queues to new stream queues if needed,
  * but not across associations. Also, removes those chunks to streams
  * higher than the new max.
@@ -70,16 +79,14 @@ static void sctp_stream_outq_migrate(struct
sctp_stream *stream,
                 * sctp_stream_update will swap ->out pointers.
                 */
                for (i = 0; i < outcnt; i++) {
-                       kfree(SCTP_SO(new, i)->ext);
+                       sctp_stream_free_ext(new, i);
                        SCTP_SO(new, i)->ext = SCTP_SO(stream, i)->ext;
                        SCTP_SO(stream, i)->ext = NULL;
                }
        }

-       for (i = outcnt; i < stream->outcnt; i++) {
-               kfree(SCTP_SO(stream, i)->ext);
-               SCTP_SO(stream, i)->ext = NULL;
-       }
+       for (i = outcnt; i < stream->outcnt; i++)
+               sctp_stream_free_ext(new, i);
 }

Marcelo, do you see a better solution?

Thanks.