sctp: avoid running the sctp state machine recursively [Linux 5.1]

sctp: avoid running the sctp state machine recursively [Linux 5.1]

This Linux kernel change "sctp: avoid running the sctp state machine recursively" is included in the Linux 5.1 release. This change is authored by Xin Long <lucien.xin [at] gmail.com> on Mon Apr 29 14:16:19 2019 +0800. The commit for this change in Linux stable tree is fbd0197 (patch).

sctp: avoid running the sctp state machine recursively

Ying triggered a call trace when doing an asconf testing:

  BUG: scheduling while atomic: swapper/12/0/0x10000100
  Call Trace:
   <IRQ>  [<ffffffffa4375904>] dump_stack+0x19/0x1b
   [<ffffffffa436fcaf>] __schedule_bug+0x64/0x72
   [<ffffffffa437b93a>] __schedule+0x9ba/0xa00
   [<ffffffffa3cd5326>] __cond_resched+0x26/0x30
   [<ffffffffa437bc4a>] _cond_resched+0x3a/0x50
   [<ffffffffa3e22be8>] kmem_cache_alloc_node+0x38/0x200
   [<ffffffffa423512d>] __alloc_skb+0x5d/0x2d0
   [<ffffffffc0995320>] sctp_packet_transmit+0x610/0xa20 [sctp]
   [<ffffffffc098510e>] sctp_outq_flush+0x2ce/0xc00 [sctp]
   [<ffffffffc098646c>] sctp_outq_uncork+0x1c/0x20 [sctp]
   [<ffffffffc0977338>] sctp_cmd_interpreter.isra.22+0xc8/0x1460 [sctp]
   [<ffffffffc0976ad1>] sctp_do_sm+0xe1/0x350 [sctp]
   [<ffffffffc099443d>] sctp_primitive_ASCONF+0x3d/0x50 [sctp]
   [<ffffffffc0977384>] sctp_cmd_interpreter.isra.22+0x114/0x1460 [sctp]
   [<ffffffffc0976ad1>] sctp_do_sm+0xe1/0x350 [sctp]
   [<ffffffffc097b3a4>] sctp_assoc_bh_rcv+0xf4/0x1b0 [sctp]
   [<ffffffffc09840f1>] sctp_inq_push+0x51/0x70 [sctp]
   [<ffffffffc099732b>] sctp_rcv+0xa8b/0xbd0 [sctp]

As it shows, the first sctp_do_sm() running under atomic context (NET_RX
softirq) invoked sctp_primitive_ASCONF() that uses GFP_KERNEL flag later,
and this flag is supposed to be used in non-atomic context only. Besides,
sctp_do_sm() was called recursively, which is not expected.

Vlad tried to fix this recursive call in Commit c0786693404c ("sctp: Fix
oops when sending queued ASCONF chunks") by introducing a new command
SCTP_CMD_SEND_NEXT_ASCONF. But it didn't work as this command is still
used in the first sctp_do_sm() call, and sctp_primitive_ASCONF() will
be called in this command again.

To avoid calling sctp_do_sm() recursively, we send the next queued ASCONF
not by sctp_primitive_ASCONF(), but by sctp_sf_do_prm_asconf() in the 1st
sctp_do_sm() directly.

Reported-by: Ying Xu <[email protected]>
Signed-off-by: Xin Long <[email protected]>
Acked-by: Neil Horman <[email protected]>
Acked-by: Marcelo Ricardo Leitner <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

There are 65 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 include/net/sctp/command.h |  1 -
 net/sctp/sm_sideeffect.c   | 29 -----------------------------
 net/sctp/sm_statefuns.c    | 35 +++++++++++++++++++++++++++--------
 3 files changed, 27 insertions(+), 38 deletions(-)

diff --git a/include/net/sctp/command.h b/include/net/sctp/command.h
index 6640f84..6d5beac 100644
--- a/include/net/sctp/command.h
+++ b/include/net/sctp/command.h
@@ -105,7 +105,6 @@ enum sctp_verb {
    SCTP_CMD_T1_RETRAN,  /* Mark for retransmission after T1 timeout  */
    SCTP_CMD_UPDATE_INITTAG, /* Update peer inittag */
    SCTP_CMD_SEND_MSG,   /* Send the whole use message */
-   SCTP_CMD_SEND_NEXT_ASCONF, /* Send the next ASCONF after ACK */
    SCTP_CMD_PURGE_ASCONF_QUEUE, /* Purge all asconf queues.*/
    SCTP_CMD_SET_ASOC,   /* Restore association context */
    SCTP_CMD_LAST
diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index 1d143bc..4aa0358 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -1112,32 +1112,6 @@ static void sctp_cmd_send_msg(struct sctp_association *asoc,
 }

-/* Sent the next ASCONF packet currently stored in the association.
- * This happens after the ASCONF_ACK was succeffully processed.
- */
-static void sctp_cmd_send_asconf(struct sctp_association *asoc)
-{
-   struct net *net = sock_net(asoc->base.sk);
-
-   /* Send the next asconf chunk from the addip chunk
-    * queue.
-    */
-   if (!list_empty(&asoc->addip_chunk_list)) {
-       struct list_head *entry = asoc->addip_chunk_list.next;
-       struct sctp_chunk *asconf = list_entry(entry,
-                       struct sctp_chunk, list);
-       list_del_init(entry);
-
-       /* Hold the chunk until an ASCONF_ACK is received. */
-       sctp_chunk_hold(asconf);
-       if (sctp_primitive_ASCONF(net, asoc, asconf))
-           sctp_chunk_free(asconf);
-       else
-           asoc->addip_last_asconf = asconf;
-   }
-}
-
-
 /* These three macros allow us to pull the debugging code out of the
  * main flow of sctp_do_sm() to keep attention focused on the real
  * functionality there.
@@ -1783,9 +1757,6 @@ static int sctp_cmd_interpreter(enum sctp_event_type event_type,
            }
            sctp_cmd_send_msg(asoc, cmd->obj.msg, gfp);
            break;
-       case SCTP_CMD_SEND_NEXT_ASCONF:
-           sctp_cmd_send_asconf(asoc);
-           break;
        case SCTP_CMD_PURGE_ASCONF_QUEUE:
            sctp_asconf_queue_teardown(asoc);
            break;
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index c9ae340..713a669 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -3824,6 +3824,29 @@ enum sctp_disposition sctp_sf_do_asconf(struct net *net,
    return SCTP_DISPOSITION_CONSUME;
 }

+static enum sctp_disposition sctp_send_next_asconf(
+                   struct net *net,
+                   const struct sctp_endpoint *ep,
+                   struct sctp_association *asoc,
+                   const union sctp_subtype type,
+                   struct sctp_cmd_seq *commands)
+{
+   struct sctp_chunk *asconf;
+   struct list_head *entry;
+
+   if (list_empty(&asoc->addip_chunk_list))
+       return SCTP_DISPOSITION_CONSUME;
+
+   entry = asoc->addip_chunk_list.next;
+   asconf = list_entry(entry, struct sctp_chunk, list);
+
+   list_del_init(entry);
+   sctp_chunk_hold(asconf);
+   asoc->addip_last_asconf = asconf;
+
+   return sctp_sf_do_prm_asconf(net, ep, asoc, type, asconf, commands);
+}
+
 /*
  * ADDIP Section 4.3 General rules for address manipulation
  * When building TLV parameters for the ASCONF Chunk that will add or
@@ -3915,14 +3938,10 @@ enum sctp_disposition sctp_sf_do_asconf_ack(struct net *net,
                SCTP_TO(SCTP_EVENT_TIMEOUT_T4_RTO));

        if (!sctp_process_asconf_ack((struct sctp_association *)asoc,
-                        asconf_ack)) {
-           /* Successfully processed ASCONF_ACK.  We can
-            * release the next asconf if we have one.
-            */
-           sctp_add_cmd_sf(commands, SCTP_CMD_SEND_NEXT_ASCONF,
-                   SCTP_NULL());
-           return SCTP_DISPOSITION_CONSUME;
-       }
+                        asconf_ack))
+           return sctp_send_next_asconf(net, ep,
+                   (struct sctp_association *)asoc,
+                           type, commands);

        abort = sctp_make_abort(asoc, asconf_ack,
                    sizeof(struct sctp_errhdr));

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