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

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>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20260520114207.1394241-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index 6fd5386a1d646542c184702e13cc2e6c8ee1820d..c04a4d0889ae412a9fc3e2458faa41200f26b098 100644 (file)
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -1824,6 +1824,7 @@ static int br_fill_linkxstats(struct sk_buff *skb,
                              const struct net_device *dev,
                              int *prividx, int attr)
 {
+       unsigned int limit = U16_MAX - nla_total_size(0);
        struct nlattr *nla __maybe_unused;
        struct net_bridge_port *p = NULL;
        struct net_bridge_vlan_group *vg;
@@ -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;
 
+#ifdef CONFIG_BRIDGE_IGMP_SNOOPING
+               limit -= nla_total_size_64bit(sizeof(struct br_mcast_stats));
+#endif
                pvid = br_get_pvid(vg);
                list_for_each_entry(v, &vg->vlan_list, vlist) {
                        struct bridge_vlan_xstats vxi;
@@ -1862,6 +1867,11 @@ static int br_fill_linkxstats(struct sk_buff *skb,
 
                        if (++vl_idx < *prividx)
                                continue;
+
+                       if (skb_tail_pointer(skb) - (unsigned char *)nest +
+                           nla_total_size(sizeof(vxi)) >= limit)
+                               goto nla_put_failure;
+
                        memset(&vxi, 0, sizeof(vxi));
                        vxi.vid = v->vid;
                        vxi.flags = v->flags;

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index df042da422ef3137ed67efaf8d243cc6b1fec6c7..511c25bf6f2a25563b7dd8d618fb46c9297d2ed7 100644 (file)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -6328,8 +6328,9 @@ static int rtnl_stats_get(struct sk_buff *skb, struct nlmsghdr *nlh,
                                  NETLINK_CB(skb).portid, nlh->nlmsg_seq, 0,
                                  0, &filters, &idxattr, &prividx, extack);
        if (err < 0) {
-               /* -EMSGSIZE implies BUG in if_nlmsg_stats_size */
-               WARN_ON(err == -EMSGSIZE);
+               /* -EMSGSIZE implies BUG in if_nlmsg_stats_size
+                * or a too big nested attribute.
+                */
                kfree_skb(nskb);
        } else {
                err = rtnl_unicast(nskb, net, NETLINK_CB(skb).portid);