[PATCH v2 1/2] netfilter: ip_tables: guard ipt_unregister_table_pre_exit against NULL ops

[Tristan Madani <tristmd@gmail.com>]

ipt_register_table() adds the table to the per-netns list via
xt_register_table() before assigning the per-net ops copy to
new_table->ops.  If cleanup_net runs during this window,
ipt_unregister_table_pre_exit() finds the table via xt_find_table()
and passes the NULL ops pointer to nf_unregister_net_hooks(), causing
a general protection fault.

Guard against this by checking table->ops before calling
nf_unregister_net_hooks().  If ops is NULL the table is still being
set up; the register path will either complete and register the hooks
normally, or fail and clean up via __ipt_unregister_table().

Fixes: ae689334225f ("netfilter: xtables: Bring back xt_register_table()")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 net/ipv4/netfilter/ip_tables.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index XXXXXXX..XXXXXXX 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -1795,7 +1795,7 @@ void ipt_unregister_table_pre_exit(struct net *net, const char *name)
 {
 	struct xt_table *table = xt_find_table(net, NFPROTO_IPV4, name);

-	if (table)
+	if (table && table->ops)
 		nf_unregister_net_hooks(net, table->ops, hweight32(table->valid_hooks));
 }