[PATCH AUTOSEL 4.20 040/304] sctp: Fix SKB list traversal in sctp_intl_store_reasm().

Sasha Levin
2019-01-28T15:45:12Z

From: "David S. Miller" <davem@davemloft.net>

[ Upstream commit 348bbc25c40844c5efa083a3842c7f53d70a815e ]

To be fully correct, an iterator has an undefined value when something
like skb_queue_walk() naturally terminates.

This will actually matter when SKB queues are converted over to
list_head.

Formalize what this code ends up doing with the current
implementation.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sctp/stream_interleave.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/net/sctp/stream_interleave.c b/net/sctp/stream_interleave.c
index 500449b72eca..2b499a85db0e 100644
--- a/net/sctp/stream_interleave.c
+++ b/net/sctp/stream_interleave.c
@@ -140,7 +140,7 @@ static void sctp_intl_store_reasm(struct sctp_ulpq *ulpq,
struct sctp_ulpevent *event)
{
struct sctp_ulpevent *cevent;
- struct sk_buff *pos;
+ struct sk_buff *pos, *loc;

pos = skb_peek_tail(&ulpq->reasm);
if (!pos) {
@@ -166,23 +166,30 @@ static void sctp_intl_store_reasm(struct sctp_ulpq *ulpq,
return;
}

+ loc = NULL;
skb_queue_walk(&ulpq->reasm, pos) {
cevent = sctp_skb2event(pos);

if (event->stream < cevent->stream ||
(event->stream == cevent->stream &&
- MID_lt(event->mid, cevent->mid)))
+ MID_lt(event->mid, cevent->mid))) {
+ loc = pos;
break;
-
+ }
if (event->stream == cevent->stream &&
event->mid == cevent->mid &&
!(cevent->msg_flags & SCTP_DATA_FIRST_FRAG) &&
(event->msg_flags & SCTP_DATA_FIRST_FRAG ||
- event->fsn < cevent->fsn))
+ event->fsn < cevent->fsn)) {
+ loc = pos;
break;
+ }
}

- __skb_queue_before(&ulpq->reasm, pos, sctp_event2skb(event));
+ if (!loc)
+ __skb_queue_tail(&ulpq->reasm, sctp_event2skb(event));
+ else
+ __skb_queue_before(&ulpq->reasm, loc, sctp_event2skb(event));
}

static struct sctp_ulpevent *sctp_intl_retrieve_partial(
--
2.19.1