[Devel] [PATCH RHEL7 COMMIT] ms/netfilter: ipset: fix suspicious RCU usage in find_set_and_id

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1160.6.1.vz7.171.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.6.1.vz7.171.1
------>
commit f5f65619105ec0a399f04afb47045100d887ed46
Author: Kadlecsik József <kadlec at blackhole.kfki.hu>
Date:   Thu Dec 3 12:21:31 2020 +0300

    ms/netfilter: ipset: fix suspicious RCU usage in find_set_and_id
    
    find_set_and_id() is called when the NFNL_SUBSYS_IPSET mutex is held.
    However, in the error path there can be a follow-up recvmsg() without
    the mutex held. Use the start() function of struct netlink_dump_control
    instead of dump() to verify and report if the specified set does not
    exist.
    
    Thanks to Pablo Neira Ayuso for helping me to understand the subleties
    of the netlink protocol.
    
    Reported-by: syzbot+fc69d7cb21258ab4ae4d at syzkaller.appspotmail.com
    Signed-off-by: Jozsef Kadlecsik <kadlec at netfilter.org>
    Signed-off-by: Pablo Neira Ayuso <pablo at netfilter.org>
    
    (cherry-picked from commit 5038517119d50ed0240059b1d7fc2faa92371c08)
    https://jira.sw.ru/browse/PSBM-122965
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 net/netfilter/ipset/ip_set_core.c | 41 ++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index 0a53827..a22af3e 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -1284,30 +1284,33 @@ dump_attrs(struct nlmsghdr *nlh)
 }
 
 static int
-dump_init(struct netlink_callback *cb, struct ip_set_net *inst)
+ip_set_dump_start(struct netlink_callback *cb)
 {
 	struct nlmsghdr *nlh = nlmsg_hdr(cb->skb);
 	int min_len = nlmsg_total_size(sizeof(struct nfgenmsg));
 	struct nlattr *cda[IPSET_ATTR_CMD_MAX + 1];
 	struct nlattr *attr = (void *)nlh + min_len;
+	struct sk_buff *skb = cb->skb;
+	struct ip_set_net *inst = ip_set_pernet(sock_net(skb->sk));
 	u32 dump_type;
-	ip_set_id_t index;
 	int ret;
 
 	ret = nla_parse(cda, IPSET_ATTR_CMD_MAX,
 		  attr, nlh->nlmsg_len - min_len, ip_set_setname_policy);
 	if (ret)
-		return ret;
+		goto error;
 
 	cb->args[IPSET_CB_PROTO] = nla_get_u8(cda[IPSET_ATTR_PROTOCOL]);
 	if (cda[IPSET_ATTR_SETNAME]) {
+		ip_set_id_t index;
 		struct ip_set *set;
 
 		set = find_set_and_id(inst, nla_data(cda[IPSET_ATTR_SETNAME]),
 				      &index);
-		if (!set)
-			return -ENOENT;
-
+		if (!set) {
+			ret = -ENOENT;
+			goto error;
+		}
 		dump_type = DUMP_ONE;
 		cb->args[IPSET_CB_INDEX] = index;
 	} else {
@@ -1323,10 +1326,17 @@ dump_init(struct netlink_callback *cb, struct ip_set_net *inst)
 	cb->args[IPSET_CB_DUMP] = dump_type;
 
 	return 0;
+
+error:
+	/* We have to create and send the error message manually :-( */
+	if (nlh->nlmsg_flags & NLM_F_ACK) {
+		netlink_ack(cb->skb, nlh, ret);
+	}
+	return ret;
 }
 
 static int
-ip_set_dump_start(struct sk_buff *skb, struct netlink_callback *cb)
+ip_set_dump_do(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	ip_set_id_t index = IPSET_INVALID_ID, max;
 	struct ip_set *set = NULL;
@@ -1337,18 +1347,8 @@ ip_set_dump_start(struct sk_buff *skb, struct netlink_callback *cb)
 	bool is_destroyed;
 	int ret = 0;
 
-	if (!cb->args[IPSET_CB_DUMP]) {
-		ret = dump_init(cb, inst);
-		if (ret < 0) {
-			nlh = nlmsg_hdr(cb->skb);
-			/* We have to create and send the error message
-			 * manually :-(
-			 */
-			if (nlh->nlmsg_flags & NLM_F_ACK)
-				netlink_ack(cb->skb, nlh, ret);
-			return ret;
-		}
-	}
+	if (!cb->args[IPSET_CB_DUMP])
+		return -EINVAL;
 
 	if (cb->args[IPSET_CB_INDEX] >= inst->ip_set_max)
 		goto out;
@@ -1484,7 +1484,8 @@ ip_set_dump(struct sock *ctnl, struct sk_buff *skb,
 
 	{
 		struct netlink_dump_control c = {
-			.dump = ip_set_dump_start,
+			.start = ip_set_dump_start,
+			.dump = ip_set_dump_do,
 			.done = ip_set_dump_done,
 		};
 		return netlink_dump_start(ctnl, skb, nlh, &c);