macsec: don't free NULL metadata_dst

Commit 7147f26cccd6 added a metadata_dst to each tx_sc, but that's
only allocated when macsec_add_dev has run, which happens after device
registration. If the requested or computed SCI already exists, or if
linking to the lower device fails, we will panic because
metadata_dst_free can't handle NULL.

Reproducer:
    ip link add link $lower type macsec
    ip link add link $lower type macsec

Fixes: 7147f26cccd6 ("net/macsec: Add MACsec skb_metadata_dst Tx Data path support")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Raed Salem <raeds@nvidia.com>
Link: https://lore.kernel.org/r/60f2a1965fe553e2cade9472407d0fafff8de8ce.1663923580.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 8193ab39206f3afed4944ddbc1d55b7eaf7e9785..c891b60937a7f0118147fc6b1e27f78f0df6ab0d 100644 (file)
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -3720,7 +3720,8 @@ static void macsec_free_netdev(struct net_device *dev)
 {
        struct macsec_dev *macsec = macsec_priv(dev);
 
-       metadata_dst_free(macsec->secy.tx_sc.md_dst);
+       if (macsec->secy.tx_sc.md_dst)
+               metadata_dst_free(macsec->secy.tx_sc.md_dst);
        free_percpu(macsec->stats);
        free_percpu(macsec->secy.tx_sc.stats);