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. If bpf_redirect_neigh() is called with explicit AF_INET6
nexthop parameters, __bpf_redirect_neigh_v6() can skip the IPv6 FIB lookup
and call bpf_out_neigh_v6() directly. bpf_out_neigh_v6() then calls
ip_neigh_gw6(), which uses ipv6_stub->nd_tbl.
BUG: kernel NULL pointer dereference, address: 0000000000000248
Oops: Oops: 0000 [#1] SMP NOPTI
RIP: 0010:skb_do_redirect+0x44f/0xf40
Call Trace:
? srso_alias_return_thunk+0x5/0xfbef5
? __tcf_classify.constprop.0+0x83/0x160
? srso_alias_return_thunk+0x5/0xfbef5
? tcf_classify+0x2b/0x50
? srso_alias_return_thunk+0x5/0xfbef5
? tc_run+0xb8/0x120
? srso_alias_return_thunk+0x5/0xfbef5
__dev_queue_xmit+0x6fa/0x1000
? srso_alias_return_thunk+0x5/0xfbef5
packet_sendmsg+0x10da/0x1700
? srso_alias_return_thunk+0x5/0xfbef5
__sys_sendto+0x1f3/0x220
__x64_sys_sendto+0x24/0x30
do_syscall_64+0x101/0xf80
? exc_page_fault+0x6e/0x170
? srso_alias_return_thunk+0x5/0xfbef5
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Fix this by adding an early check in bpf_out_neigh_v6(). If
ipv6_stub->nd_tbl is NULL, drop the packet before neighbor lookup.
Suggested-by: Fernando Fernandez Mancera
Fixes: ba452c9e996d ("bpf: Fix bpf_redirect_neigh helper api to support supplying nexthop")
Signed-off-by: Ricardo B. Marlière
---
net/core/filter.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/core/filter.c b/net/core/filter.c
index ff02dbe4c94f..3344fa0789f0 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2228,6 +2228,9 @@ static int bpf_out_neigh_v6(struct net *net, struct sk_buff *skb,
return -ENOMEM;
}
+ if (unlikely(!ipv6_mod_enabled()))
+ goto out_drop;
+
rcu_read_lock();
if (!nh) {
dst = skb_dst(skb);
--
2.53.0