[PATCH net] net: bridge: prevent too big nested attributes in br_fill_linkxstats()

[Eric Dumazet <edumazet@google.com>]

After commit ff205bf8c554 ("netlink: add one debug check in nla_nest_end()")
syzbot found that br_fill_linkxstats() can send corrupted netlink packets.

Make sure the nested attribute size is bounded.

Fixes: a60c090361ea ("bridge: netlink: export per-vlan stats")
Reported-by: syzbot+a35f9259d08f907c06e6@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a0b0da3.050a0220.175f0c.0000.GAE@google.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
Cc: Nikolay Aleksandrov <razor@blackwall.org>
Cc: Ido Schimmel <idosch@nvidia.com>
---
 net/bridge/br_netlink.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index 6fd5386a1d646542c184702e13cc2e6c8ee1820d..e15a08a34aeab2429b6c49c5a0ecab9b47582f06 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -1827,6 +1827,7 @@ static int br_fill_linkxstats(struct sk_buff *skb,
 	struct nlattr *nla __maybe_unused;
 	struct net_bridge_port *p = NULL;
 	struct net_bridge_vlan_group *vg;
+	unsigned int limit = U16_MAX;
 	struct net_bridge_vlan *v;
 	struct net_bridge *br;
 	struct nlattr *nest;
@@ -1841,6 +1842,7 @@ static int br_fill_linkxstats(struct sk_buff *skb,
 		p = br_port_get_rtnl(dev);
 		if (!p)
 			return 0;
+		limit -= nla_total_size_64bit(sizeof(p->stp_xstats));
 		br = p->br;
 		vg = nbp_vlan_group(p);
 		break;
@@ -1855,6 +1857,9 @@ static int br_fill_linkxstats(struct sk_buff *skb,
 	if (vg) {
 		u16 pvid;
 
+		limit -= nla_total_size(sizeof(struct br_mcast_stats)) +
+			 nla_total_size_64bit(sizeof(struct br_mcast_stats));
+
 		pvid = br_get_pvid(vg);
 		list_for_each_entry(v, &vg->vlan_list, vlist) {
 			struct bridge_vlan_xstats vxi;
@@ -1862,6 +1867,10 @@ static int br_fill_linkxstats(struct sk_buff *skb,
 
 			if (++vl_idx < *prividx)
 				continue;
+
+			if (skb_tail_pointer(skb) - (unsigned char *)nest >= limit)
+				goto nla_put_failure;
+
 			memset(&vxi, 0, sizeof(vxi));
 			vxi.vid = v->vid;
 			vxi.flags = v->flags;
-- 
2.54.0.563.g4f69b47b94-goog