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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@google.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@google.com>
Cc: Petr Machata <petrm@mellanox.com>
Cc: Ido Schimmel <idosch@mellanox.com>
Cc: Roopa Prabhu <roopa@cumulusnetworks.com>
Cc: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.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,
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