netdev - [PATCH] net: 802: fix memory leak in garp_uninit

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Date:   Mon, 19 Jul 2021 00:00:06 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     davem@...emloft.net, kuba@...nel.org, kaber@...sh.net
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pavel Skripkin <paskripkin@...il.com>,
        syzbot+13ad608e190b5f8ad8a8@...kaller.appspotmail.com
Subject: [PATCH] net: 802: fix memory leak in garp_uninit_applicant

Syzbot reported memory leak in garp_uninit_applicant(). The problem was
in missing clean up function in garp_uninit_applicant().

The reproducer provided by syzbot doing following things in order:

	1. garp_request_join()
 	     garp_attr_event(app, attr, GARP_EVENT_REQ_JOIN);
		/* attr->state == GARP_APPLICANT_VP */

	2. garp_request_leave()
	     garp_attr_event(app, attr, GARP_EVENT_REQ_LEAVE);
		/* attr->state == GARP_APPLICANT_VO */

	3. garp_uninit_applicant()
	     garp_gid_event(app, GARP_EVENT_TRANSMIT_PDU);
  		/* attr is not freed */

Why attr won't be freed? Let's refer to garp_applicant_state_table:

[GARP_APPLICANT_VO] = {
	[GARP_EVENT_TRANSMIT_PDU]	= { .state = GARP_APPLICANT_INVALID },
	[GARP_EVENT_R_JOIN_IN]		= { .state = GARP_APPLICANT_AO },
	[GARP_EVENT_R_JOIN_EMPTY]	= { .state = GARP_APPLICANT_VO },
	[GARP_EVENT_R_EMPTY]		= { .state = GARP_APPLICANT_VO },
	[GARP_EVENT_R_LEAVE_IN]		= { .state = GARP_APPLICANT_VO },
	[GARP_EVENT_R_LEAVE_EMPTY]	= { .state = GARP_APPLICANT_VO },
	[GARP_EVENT_REQ_JOIN]		= { .state = GARP_APPLICANT_VP },
	[GARP_EVENT_REQ_LEAVE]		= { .state = GARP_APPLICANT_INVALID },

REQ_LEAVE event has INVALID state as standard says and
garp_attr_event() just returns in case of invalid state.
Since garp_uninit_applicant() is destroy function for applicant we need
to free remaining attrs to avoid memory leaks.

Fixes: eca9ebac651f ("net: Add GARP applicant-only participant")
Reported-and-tested-by: syzbot+13ad608e190b5f8ad8a8@...kaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
---
 net/802/garp.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/net/802/garp.c b/net/802/garp.c
index 400bd857e5f5..4a1ef95ae428 100644
--- a/net/802/garp.c
+++ b/net/802/garp.c
@@ -553,6 +553,16 @@ static void garp_release_port(struct net_device *dev)
 	kfree_rcu(port, rcu);
 }
 
+static void garp_destroy_remaining_attrs(struct garp_applicant *app)
+{
+	while (!RB_EMPTY_ROOT(&app->gid)) {
+		struct garp_attr *attr =
+			rb_entry(rb_first(&app->gid),
+				 struct garp_attr, node);
+		garp_attr_destroy(app, attr);
+	}
+}
+
 int garp_init_applicant(struct net_device *dev, struct garp_application *appl)
 {
 	struct garp_applicant *app;
@@ -610,6 +620,13 @@ void garp_uninit_applicant(struct net_device *dev, struct garp_application *appl
 	spin_lock_bh(&app->lock);
 	garp_gid_event(app, GARP_EVENT_TRANSMIT_PDU);
 	garp_pdu_queue(app);
+
+	/* We need to free remaining attrs since this scenario is possible:
+	 *	garp_request_join()
+	 *	garp_request_leave()
+	 *	garp_uninit_applicant()
+	 */
+	garp_destroy_remaining_attrs(app);
 	spin_unlock_bh(&app->lock);
 
 	garp_queue_xmit(app);
-- 
2.32.0