netdev - [PATCH 7/9] l2tp: WARN_ON rather than BUG_ON in l2tp_session_queue

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Date:   Fri, 24 Jul 2020 16:31:55 +0100
From:   Tom Parkin <tparkin@...alix.com>
To:     netdev@...r.kernel.org
Cc:     jchapman@...alix.com, Tom Parkin <tparkin@...alix.com>
Subject: [PATCH 7/9] l2tp: WARN_ON rather than BUG_ON in l2tp_session_queue_purge

l2tp_session_queue_purge is used during session shutdown to drop any
skbs queued for reordering purposes according to L2TP dataplane rules.

The BUG_ON in this function checks the session magic feather in an
attempt to catch lifetime bugs.

Rather than crashing the kernel with a BUG_ON, we can simply WARN_ON and
refuse to do anything more -- in the worst case this could result in a
leak.  However this is highly unlikely given that the session purge only
occurs from codepaths which have obtained the session by means of a lookup
via. the parent tunnel and which check the session "dead" flag to
protect against shutdown races.

While we're here, have l2tp_session_queue_purge return void rather than
an integer, since neither of the callsites checked the return value.

Signed-off-by: Tom Parkin <tparkin@...alix.com>
---
 net/l2tp/l2tp_core.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 6be3f2e69efd..e228480fa529 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -773,16 +773,17 @@ EXPORT_SYMBOL(l2tp_recv_common);

 /* Drop skbs from the session's reorder_q
  */
-static int l2tp_session_queue_purge(struct l2tp_session *session)
+static void l2tp_session_queue_purge(struct l2tp_session *session)
 {
 	struct sk_buff *skb = NULL;

-	BUG_ON(session->magic != L2TP_SESSION_MAGIC);
+	if (WARN_ON(session->magic != L2TP_SESSION_MAGIC))
+		return;
+
 	while ((skb = skb_dequeue(&session->reorder_q))) {
 		atomic_long_inc(&session->stats.rx_errors);
 		kfree_skb(skb);
 	}
-	return 0;
 }

 /* Internal UDP receive frame. Do the real work of receiving an L2TP data frame
-- 
2.17.1