net: macsec: fix double free of percpu stats

Inside macsec_add_dev() we free percpu macsec->secy.tx_sc.stats and
macsec->stats on some of the memory allocation failure paths. However, the
net_device is already registered to that moment: in macsec_newlink(), just
before calling macsec_add_dev(). This means that during unregister process
its priv_destructor - macsec_free_netdev() - will be called and will free
the stats again.

Remove freeing percpu stats inside macsec_add_dev() because
macsec_free_netdev() will correctly free the already allocated ones. The
pointers to unallocated stats stay NULL, and free_percpu() treats that
correctly.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 0a28bfd ("net/macsec: Add MACsec skb_metadata_dst Tx Data path support")
Fixes: c09440f ("macsec: introduce IEEE 802.1AE driver")
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: pchelkin91

drivers/net/macsec.c

@@ -3997,17 +3997,15 @@ static int macsec_add_dev(struct net_device *dev, sci_t sci, u8 icv_len)
 		return -ENOMEM;
 
 	secy->tx_sc.stats = netdev_alloc_pcpu_stats(struct pcpu_tx_sc_stats);
-	if (!secy->tx_sc.stats) {
-		free_percpu(macsec->stats);
+	if (!secy->tx_sc.stats)
 		return -ENOMEM;
-	}
 
 	secy->tx_sc.md_dst = metadata_dst_alloc(0, METADATA_MACSEC, GFP_KERNEL);
-	if (!secy->tx_sc.md_dst) {
-		free_percpu(secy->tx_sc.stats);
-		free_percpu(macsec->stats);
+	if (!secy->tx_sc.md_dst)
+		/* macsec and secy percpu stats will be freed when unregistering
+		 * net_device in macsec_free_netdev()
+		 */
 		return -ENOMEM;
-	}
 
 	if (sci == MACSEC_UNDEF_SCI)
 		sci = dev_to_sci(dev, MACSEC_PORT_ES);