ila: serialize calls to nf_register_net_hooks()

syzbot found a race in ila_add_mapping() [1]

commit 031ae72825ce ("ila: call nf_unregister_net_hooks() sooner")
attempted to fix a similar issue.

Looking at the syzbot repro, we have concurrent ILA_CMD_ADD commands.

Add a mutex to make sure at most one thread is calling nf_register_net_hooks().

[1]
BUG: KASAN: slab-use-after-free in rht_key_hashfn include/linux/rhashtable.h:159 [inline]
BUG: KASAN: slab-use-after-free in __rhashtable_lookup.constprop.0+0x426/0x550 include/linux/rhashtable.h:604
Read of size 4 at addr ffff888028f40008 by task dhcpcd/5501

CPU: 1 UID: 0 PID: 5501 Comm: dhcpcd Not tainted 6.13.0-rc4-syzkaller-00054-gd6ef8b40d075 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xc3/0x620 mm/kasan/report.c:489
kasan_report+0xd9/0x110 mm/kasan/report.c:602
rht_key_hashfn include/linux/rhashtable.h:159 [inline]
__rhashtable_lookup.constprop.0+0x426/0x550 include/linux/rhashtable.h:604
rhashtable_lookup include/linux/rhashtable.h:646 [inline]
rhashtable_lookup_fast include/linux/rhashtable.h:672 [inline]
ila_lookup_wildcards net/ipv6/ila/ila_xlat.c:127 [inline]
ila_xlat_addr net/ipv6/ila/ila_xlat.c:652 [inline]
ila_nf_input+0x1ee/0x620 net/ipv6/ila/ila_xlat.c:185
nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
nf_hook_slow+0xbb/0x200 net/netfilter/core.c:626
nf_hook.constprop.0+0x42e/0x750 include/linux/netfilter.h:269
NF_HOOK include/linux/netfilter.h:312 [inline]
ipv6_rcv+0xa4/0x680 net/ipv6/ip6_input.c:309
__netif_receive_skb_one_core+0x12e/0x1e0 net/core/dev.c:5672
__netif_receive_skb+0x1d/0x160 net/core/dev.c:5785
process_backlog+0x443/0x15f0 net/core/dev.c:6117
__napi_poll.constprop.0+0xb7/0x550 net/core/dev.c:6883
napi_poll net/core/dev.c:6952 [inline]
net_rx_action+0xa94/0x1010 net/core/dev.c:7074
handle_softirqs+0x213/0x8f0 kernel/softirq.c:561
__do_softirq kernel/softirq.c:595 [inline]
invoke_softirq kernel/softirq.c:435 [inline]
__irq_exit_rcu+0x109/0x170 kernel/softirq.c:662
irq_exit_rcu+0x9/0x30 kernel/softirq.c:678
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1049

Fixes: 7f00feaf1076 ("ila: Add generic ILA translation facility")
Reported-by: [e-mail]
Closes: https://lore.kernel.org/netdev/[e-mail]/T/#u
Signed-off-by: Eric Dumazet <[e-mail]>
Cc: Florian Westphal <[e-mail]>
Cc: Tom Herbert <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ipv6/ila/ila_xlat.c

···
 	},
 };
 
+static DEFINE_MUTEX(ila_mutex);
+
 static int ila_add_mapping(struct net *net, struct ila_xlat_params *xp)
 {
 	struct ila_net *ilan = net_generic(net, ila_net_id);
···
 	spinlock_t *lock = ila_get_lock(ilan, xp->ip.locator_match);
 	int err = 0, order;
 
-	if (!ilan->xlat.hooks_registered) {
+	if (!READ_ONCE(ilan->xlat.hooks_registered)) {
 		/* We defer registering net hooks in the namespace until the
 		 * first mapping is added.
 		 */
-		err = nf_register_net_hooks(net, ila_nf_hook_ops,
-					    ARRAY_SIZE(ila_nf_hook_ops));
+		mutex_lock(&ila_mutex);
+		if (!ilan->xlat.hooks_registered) {
+			err = nf_register_net_hooks(net, ila_nf_hook_ops,
+						ARRAY_SIZE(ila_nf_hook_ops));
+			if (!err)
+				WRITE_ONCE(ilan->xlat.hooks_registered, true);
+		}
+		mutex_unlock(&ila_mutex);
 		if (err)
 			return err;
-
-		ilan->xlat.hooks_registered = true;
 	}
 
 	ila = kzalloc(sizeof(*ila), GFP_KERNEL);