[PATCH 1/2 net v2] net: bridge: fix nd_tbl NULL dereference when IPv6 is disabled

When booting with the 'ipv6.disable=1' parameter, the nd_tbl is never
initialized because inet6_init() exits before ndisc_init() is called
which initializes it. Then, if neigh_suppress is enabled and an ICMPv6
Neighbor Discovery packet reaches the bridge, br_do_suppress_nd() will
dereference ipv6_stub->nd_tbl which is NULL, passing it to
neigh_lookup(). This causes a kernel NULL pointer dereference.

 BUG: kernel NULL pointer dereference, address: 0000000000000268
 Oops: 0000 [#1] PREEMPT SMP NOPTI
 [...]
 RIP: 0010:neigh_lookup+0x16/0xe0
 [...]
 Call Trace:
  <IRQ>
  ? neigh_lookup+0x16/0xe0
  br_do_suppress_nd+0x160/0x290 [bridge]
  br_handle_frame_finish+0x500/0x620 [bridge]
  br_handle_frame+0x353/0x440 [bridge]
  __netif_receive_skb_core.constprop.0+0x298/0x1110
  __netif_receive_skb_one_core+0x3d/0xa0
  process_backlog+0xa0/0x140
  __napi_poll+0x2c/0x170
  net_rx_action+0x2c4/0x3a0
  handle_softirqs+0xd0/0x270
  do_softirq+0x3f/0x60

Fix this by replacing IS_ENABLED(IPV6) call with ipv6_mod_enabled() in
the callers. This is in essence disabling NS/NA suppression when IPv6 is
disabled.

Fixes: ed842faeb2bd ("bridge: suppress nd pkts on BR_NEIGH_SUPPRESS ports")
Reported-by: Guruprasad C P <[email protected]>
Closes: https://lore.kernel.org/netdev/CAHXs0ORzd62QOG-Fttqa2Cx_A_VFp=utE2H2VTX5nqfgs7LDxQ@mail.gmail.com/
Signed-off-by: Fernando Fernandez Mancera <[email protected]>
---
v2: use ipv6_mod_enabled() instead of a null check and replace the check
on the caller
---
 net/bridge/br_device.c | 2 +-
 net/bridge/br_input.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index ee01122f466f..f7502e62dd35 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -74,7 +74,7 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 	     eth_hdr(skb)->h_proto == htons(ETH_P_RARP)) &&
 	    br_opt_get(br, BROPT_NEIGH_SUPPRESS_ENABLED)) {
 		br_do_proxy_suppress_arp(skb, br, vid, NULL);
-	} else if (IS_ENABLED(CONFIG_IPV6) &&
+	} else if (ipv6_mod_enabled() &&
 		   skb->protocol == htons(ETH_P_IPV6) &&
 		   br_opt_get(br, BROPT_NEIGH_SUPPRESS_ENABLED) &&
 		   pskb_may_pull(skb, sizeof(struct ipv6hdr) +
diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index 1405f1061a54..2cbae0f9ae1f 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -170,7 +170,7 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
 	    (skb->protocol == htons(ETH_P_ARP) ||
 	     skb->protocol == htons(ETH_P_RARP))) {
 		br_do_proxy_suppress_arp(skb, br, vid, p);
-	} else if (IS_ENABLED(CONFIG_IPV6) &&
+	} else if (ipv6_mod_enabled() &&
 		   skb->protocol == htons(ETH_P_IPV6) &&
 		   br_opt_get(br, BROPT_NEIGH_SUPPRESS_ENABLED) &&
 		   pskb_may_pull(skb, sizeof(struct ipv6hdr) +
-- 
2.53.0