sctp: add a refcnt in sctp_stream_priorities to avoid a nested loop

[ Upstream commit c862ae98a2901b08e83d2210e5099ddeff3fc47d ]

With this refcnt added in sctp_stream_priorities, we don't need to
traverse all streams to check if the prio is used by other streams
when freeing one stream's prio in sctp_sched_prio_free_sid(). This
can avoid a nested loop (up to 65535 * 65535), which may cause a
stuck as Ying reported:

    watchdog: BUG: soft lockup - CPU#23 stuck for 26s! [ksoftirqd/23:136]
    Call Trace:
     <TASK>
     sctp_sched_prio_free_sid+0xab/0x100 [sctp]
     sctp_stream_free_ext+0x64/0xa0 [sctp]
     sctp_stream_free+0x31/0x50 [sctp]
     sctp_association_free+0xa5/0x200 [sctp]

Note that it doesn't need to use refcount_t type for this counter,
as its accessing is always protected under the sock lock.

v1->v2:
 - add a check in sctp_sched_prio_set to avoid the possible prio_head
   refcnt overflow.

Fixes: 65c462b7f2f8 ("sctp: fix memory leak in sctp_stream_outq_migrate()")
Reported-by: Ying Xu <yinxu@redhat.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Link: https://lore.kernel.org/r/825eb0c905cb864991eba335f4a2b780e543f06b.1677085641.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 350f250b0dc75bc7dfd78a081e05ebbaafe58b20..00ee9eb601a6f08a52319c89fc898d288d660548 100644 (file)
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -1409,6 +1409,7 @@ struct sctp_stream_priorities {
        /* The next stream in line */
        struct sctp_stream_out_ext *next;
        __u16 prio;
+       __u16 users;
 };
 
 struct sctp_stream_out_ext {

diff --git a/net/sctp/stream_sched_prio.c b/net/sctp/stream_sched_prio.c
index 4fc9f2923ed116cbc02bc2e9d4771c888588fe8c..7dd9f8b387cca4099e5488bdaef0286c9cf4ca11 100644 (file)
--- a/net/sctp/stream_sched_prio.c
+++ b/net/sctp/stream_sched_prio.c
@@ -25,6 +25,18 @@
 
 static void sctp_sched_prio_unsched_all(struct sctp_stream *stream);
 
+static struct sctp_stream_priorities *sctp_sched_prio_head_get(struct sctp_stream_priorities *p)
+{
+       p->users++;
+       return p;
+}
+
+static void sctp_sched_prio_head_put(struct sctp_stream_priorities *p)
+{
+       if (p && --p->users == 0)
+               kfree(p);
+}
+
 static struct sctp_stream_priorities *sctp_sched_prio_new_head(
                        struct sctp_stream *stream, int prio, gfp_t gfp)
 {
@@ -38,6 +50,7 @@ static struct sctp_stream_priorities *sctp_sched_prio_new_head(
        INIT_LIST_HEAD(&p->active);
        p->next = NULL;
        p->prio = prio;
+       p->users = 1;
 
        return p;
 }
@@ -53,7 +66,7 @@ static struct sctp_stream_priorities *sctp_sched_prio_get_head(
         */
        list_for_each_entry(p, &stream->prio_list, prio_sched) {
                if (p->prio == prio)
-                       return p;
+                       return sctp_sched_prio_head_get(p);
                if (p->prio > prio)
                        break;
        }
@@ -70,7 +83,7 @@ static struct sctp_stream_priorities *sctp_sched_prio_get_head(
                         */
                        break;
                if (p->prio == prio)
-                       return p;
+                       return sctp_sched_prio_head_get(p);
        }
 
        /* If not even there, allocate a new one. */
@@ -154,32 +167,21 @@ static int sctp_sched_prio_set(struct sctp_stream *stream, __u16 sid,
        struct sctp_stream_out_ext *soute = sout->ext;
        struct sctp_stream_priorities *prio_head, *old;
        bool reschedule = false;
-       int i;
+
+       old = soute->prio_head;
+       if (old && old->prio == prio)
+               return 0;
 
        prio_head = sctp_sched_prio_get_head(stream, prio, gfp);
        if (!prio_head)
                return -ENOMEM;
 
        reschedule = sctp_sched_prio_unsched(soute);
-       old = soute->prio_head;
        soute->prio_head = prio_head;
        if (reschedule)
                sctp_sched_prio_sched(stream, soute);
 
-       if (!old)
-               /* Happens when we set the priority for the first time */
-               return 0;
-
-       for (i = 0; i < stream->outcnt; i++) {
-               soute = SCTP_SO(stream, i)->ext;
-               if (soute && soute->prio_head == old)
-                       /* It's still in use, nothing else to do here. */
-                       return 0;
-       }
-
-       /* No hits, we are good to free it. */
-       kfree(old);
-
+       sctp_sched_prio_head_put(old);
        return 0;
 }
 
@@ -206,20 +208,8 @@ static int sctp_sched_prio_init_sid(struct sctp_stream *stream, __u16 sid,
 
 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_sched_prio_head_put(SCTP_SO(stream, sid)->ext->prio_head);
        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)