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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
        "Gong, Sishuai" <sishuai@purdue.edu>,
        Willem de Bruijn <willemb@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.12 578/677] net/packet: remove data races in fanout operations
Date:   Wed, 12 May 2021 16:50:24 +0200
Message-Id: <20210512144856.591873791@linuxfoundation.org>
In-Reply-To: <20210512144837.204217980@linuxfoundation.org>
References: <20210512144837.204217980@linuxfoundation.org>
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From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 94f633ea8ade8418634d152ad0931133338226f6 ]

af_packet fanout uses RCU rules to ensure f->arr elements
are not dismantled before RCU grace period.

However, it lacks rcu accessors to make sure KCSAN and other tools
wont detect data races. Stupid compilers could also play games.

Fixes: dc99f600698d ("packet: Add fanout support.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: "Gong, Sishuai" <sishuai@purdue.edu>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/packet/af_packet.c | 15 +++++++++------
 net/packet/internal.h  |  2 +-
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index e24b2841c643..9611e41c7b8b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1359,7 +1359,7 @@ static unsigned int fanout_demux_rollover(struct packet_fanout *f,
 	struct packet_sock *po, *po_next, *po_skip = NULL;
 	unsigned int i, j, room = ROOM_NONE;
 
-	po = pkt_sk(f->arr[idx]);
+	po = pkt_sk(rcu_dereference(f->arr[idx]));
 
 	if (try_self) {
 		room = packet_rcv_has_room(po, skb);
@@ -1371,7 +1371,7 @@ static unsigned int fanout_demux_rollover(struct packet_fanout *f,
 
 	i = j = min_t(int, po->rollover->sock, num - 1);
 	do {
-		po_next = pkt_sk(f->arr[i]);
+		po_next = pkt_sk(rcu_dereference(f->arr[i]));
 		if (po_next != po_skip && !READ_ONCE(po_next->pressure) &&
 		    packet_rcv_has_room(po_next, skb) == ROOM_NORMAL) {
 			if (i != j)
@@ -1466,7 +1466,7 @@ static int packet_rcv_fanout(struct sk_buff *skb, struct net_device *dev,
 	if (fanout_has_flag(f, PACKET_FANOUT_FLAG_ROLLOVER))
 		idx = fanout_demux_rollover(f, skb, idx, true, num);
 
-	po = pkt_sk(f->arr[idx]);
+	po = pkt_sk(rcu_dereference(f->arr[idx]));
 	return po->prot_hook.func(skb, dev, &po->prot_hook, orig_dev);
 }
 
@@ -1480,7 +1480,7 @@ static void __fanout_link(struct sock *sk, struct packet_sock *po)
 	struct packet_fanout *f = po->fanout;
 
 	spin_lock(&f->lock);
-	f->arr[f->num_members] = sk;
+	rcu_assign_pointer(f->arr[f->num_members], sk);
 	smp_wmb();
 	f->num_members++;
 	if (f->num_members == 1)
@@ -1495,11 +1495,14 @@ static void __fanout_unlink(struct sock *sk, struct packet_sock *po)
 
 	spin_lock(&f->lock);
 	for (i = 0; i < f->num_members; i++) {
-		if (f->arr[i] == sk)
+		if (rcu_dereference_protected(f->arr[i],
+					      lockdep_is_held(&f->lock)) == sk)
 			break;
 	}
 	BUG_ON(i >= f->num_members);
-	f->arr[i] = f->arr[f->num_members - 1];
+	rcu_assign_pointer(f->arr[i],
+			   rcu_dereference_protected(f->arr[f->num_members - 1],
+						     lockdep_is_held(&f->lock)));
 	f->num_members--;
 	if (f->num_members == 0)
 		__dev_remove_pack(&f->prot_hook);
diff --git a/net/packet/internal.h b/net/packet/internal.h
index 5f61e59ebbff..48af35b1aed2 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -94,7 +94,7 @@ struct packet_fanout {
 	spinlock_t		lock;
 	refcount_t		sk_ref;
 	struct packet_type	prot_hook ____cacheline_aligned_in_smp;
-	struct sock		*arr[];
+	struct sock	__rcu	*arr[];
 };
 
 struct packet_rollover {
-- 
2.30.2