[PATCH] netfilter: ipset: wait for xt_recseq on all cpus

[xiaolinkui <xiaolinkui@126.com>]

From: Linkui Xiao <xiaolinkui@kylinos.cn>

Before destroying the ipset, take a check on sequence to ensure that the
ip_set_test operation of this ipset has been completed.

The code of set_match_v4 is protected by addend=xt_write_recseq_begin() and
xt_write_recseq_end(addend). So we can ensure that the test operation is
completed by reading seqcount.

Otherwise, there will be a low probability of use-after-free problems
occurring:

 PC: ffff0000033c0168  [hash_net4_kadt+56]
 LR: ffff000002b811bc  [ip_set_test+188]
 SP: ffff8003fff3f8d0  PSTATE: 60400005
X29: ffff8003fff3f8d0  X28: ffff8003ab915c4e  X27: ffff8003b0c7a000
X26: ffff8003b9780040  X25: ffff000000c70600  X24: ffff8003ac2c0200
X23: ffff000002f70fcc  X22: 0000000000000002  X21: ffff8003ac2c0200
X20: ffff8003be8e2800  X19: ffff8003fff3f9c8  X18: 0000000000000000
X17: 0000000000000000  X16: 0000000000000000  X15: 0000000000000000
X14: 970000002d494600  X13: 0000000000000000  X12: c5d405f139e6e418
X11: ffff000000c70600  X10: ffff8003b0c7a000   X9: 0000000000000001
 X8: 0000000000000000   X7: 000000000000005f   X6: 0000000000000000
 X5: ffff0000033c0130   X4: ffff8003fff3f9c8   X3: 0000000000000002
 X2: ffff0000033d01d8   X1: 00000000ffffffff   X0: 0000000000000000
[ffff8003fff3f8d0] hash_net4_kadt at ffff0000033c0164 [ip_set_hash_net]
[ffff8003fff3f940] ip_set_test at ffff000002b811b8 [ip_set]
[ffff8003fff3f990] set_match_v4 at ffff000002f70fc8 [xt_set]
[ffff8003fff3fa20] ipt_do_table at ffff000000c504e0 [ip_tables]
[ffff8003fff3fb60] iptable_filter_hook at ffff00000266006c [iptable_filter]
[ffff8003fff3fb80] nf_hook_slow at ffff000008ac7a84
[ffff8003fff3fbc0] ip_local_deliver at ffff000008ad5d88
[ffff8003fff3fc10] ip_rcv_finish at ffff000008ad59b4
[ffff8003fff3fc40] ip_rcv at ffff000008ad5dec
[ffff8003fff3fca0] __netif_receive_skb_one_core at ffff000008a6c344
[ffff8003fff3fce0] __netif_receive_skb at ffff000008a6c3ac
[ffff8003fff3fd00] netif_receive_skb_internal at ffff000008a6c440
[ffff8003fff3fd30] napi_gro_receive at ffff000008a6d3ec
[ffff8003fff3fd60] receive_buf at ffff000001c934d8 [virtio_net]
[ffff8003fff3fe20] virtnet_poll at ffff000001c953e8 [virtio_net]
[ffff8003fff3fec0] net_rx_action at ffff000008a6c9ec
[ffff8003fff3ff60] __softirqentry_text_start at ffff0000080819f0
[ffff8003fff3fff0] irq_exit at ffff0000080f1228
[ffff8003fff40010] __handle_domain_irq at ffff000008162a10

Signed-off-by: Linkui Xiao <xiaolinkui@kylinos.cn>
---
 net/netfilter/ipset/ip_set_core.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index 46f4f47e29e4..53561176162f 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -1187,6 +1187,24 @@ ip_set_destroy_set(struct ip_set *set)
 	kfree(set);
 }
 
+static void wait_xt_recseq(void)
+{
+	unsigned int cpu;
+
+	/* wait for even xt_recseq on all cpus */
+	for_each_possible_cpu(cpu) {
+		seqcount_t *s = &per_cpu(xt_recseq, cpu);
+		u32 seq = raw_read_seqcount(s);
+
+		if (seq & 1) {
+			do {
+				cond_resched();
+				cpu_relax();
+			} while (seq == raw_read_seqcount(s));
+		}
+	}
+}
+
 static int ip_set_destroy(struct sk_buff *skb, const struct nfnl_info *info,
 			  const struct nlattr * const attr[])
 {
@@ -1225,6 +1243,7 @@ static int ip_set_destroy(struct sk_buff *skb, const struct nfnl_info *info,
 		for (i = 0; i < inst->ip_set_max; i++) {
 			s = ip_set(inst, i);
 			if (s) {
+				wait_xt_recseq();
 				ip_set(inst, i) = NULL;
 				ip_set_destroy_set(s);
 			}
@@ -1243,6 +1262,7 @@ static int ip_set_destroy(struct sk_buff *skb, const struct nfnl_info *info,
 			ret = -IPSET_ERR_BUSY;
 			goto out;
 		}
+		wait_xt_recseq();
 		ip_set(inst, i) = NULL;
 		read_unlock_bh(&ip_set_ref_lock);
 
-- 
2.17.1