linux-kernel - [PATCH 3.16 146/202] vxlan: test dev->flags & IFF_UP before calling netif

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Message-ID: <lsq.1556377989.152990381@decadent.org.uk>
Date:   Sat, 27 Apr 2019 16:13:09 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Stefano Brivio" <sbrivio@...hat.com>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Petr Machata" <petrm@...lanox.com>,
        "Roopa Prabhu" <roopa@...ulusnetworks.com>,
        "Ido Schimmel" <idosch@...lanox.com>
Subject: [PATCH 3.16 146/202] vxlan: test dev->flags & IFF_UP before
 calling netif_rx()

3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.com>

commit 4179cb5a4c924cd233eaadd081882425bc98f44e upstream.

netif_rx() must be called under a strict contract.

At device dismantle phase, core networking clears IFF_UP
and flush_all_backlogs() is called after rcu grace period
to make sure no incoming packet might be in a cpu backlog
and still referencing the device.

Most drivers call netif_rx() from their interrupt handler,
and since the interrupts are disabled at device dismantle,
netif_rx() does not have to check dev->flags & IFF_UP

Virtual drivers do not have this guarantee, and must
therefore make the check themselves.

Otherwise we risk use-after-free and/or crashes.

Note this patch also fixes a small issue that came
with commit ce6502a8f957 ("vxlan: fix a use after free
in vxlan_encap_bypass"), since the dev->stats.rx_dropped
change was done on the wrong device.

Fixes: d342894c5d2f ("vxlan: virtual extensible lan")
Fixes: ce6502a8f957 ("vxlan: fix a use after free in vxlan_encap_bypass")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Petr Machata <petrm@...lanox.com>
Cc: Ido Schimmel <idosch@...lanox.com>
Cc: Roopa Prabhu <roopa@...ulusnetworks.com>
Cc: Stefano Brivio <sbrivio@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/vxlan.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -1772,7 +1772,7 @@ static void vxlan_encap_bypass(struct sk
 	struct pcpu_sw_netstats *tx_stats, *rx_stats;
 	union vxlan_addr loopback;
 	union vxlan_addr *remote_ip = &dst_vxlan->default_dst.remote_ip;
-	struct net_device *dev = skb->dev;
+	struct net_device *dev;
 	int len = skb->len;
 
 	tx_stats = this_cpu_ptr(src_vxlan->dev->tstats);
@@ -1792,8 +1792,15 @@ static void vxlan_encap_bypass(struct sk
 #endif
 	}
 
+	rcu_read_lock();
+	dev = skb->dev;
+	if (unlikely(!(dev->flags & IFF_UP))) {
+		kfree_skb(skb);
+		goto drop;
+	}
+
 	if (dst_vxlan->flags & VXLAN_F_LEARN)
-		vxlan_snoop(skb->dev, &loopback, eth_hdr(skb)->h_source);
+		vxlan_snoop(dev, &loopback, eth_hdr(skb)->h_source);
 
 	u64_stats_update_begin(&tx_stats->syncp);
 	tx_stats->tx_packets++;
@@ -1806,8 +1813,10 @@ static void vxlan_encap_bypass(struct sk
 		rx_stats->rx_bytes += len;
 		u64_stats_update_end(&rx_stats->syncp);
 	} else {
+drop:
 		dev->stats.rx_dropped++;
 	}
+	rcu_read_unlock();
 }
 
 static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,