tipc: do not update mtu if msg_max is too small in mtu negotiation

[ Upstream commit 56077b56cd3fb78e1c8619e29581ba25a5c55e86 ]

When doing link mtu negotiation, a malicious peer may send Activate msg
with a very small mtu, e.g. 4 in Shuang's testing, without checking for
the minimum mtu, l->mtu will be set to 4 in tipc_link_proto_rcv(), then
n->links[bearer_id].mtu is set to 4294967228, which is a overflow of
'4 - INT_H_SIZE - EMSG_OVERHEAD' in tipc_link_mss().

With tipc_link.mtu = 4, tipc_link_xmit() kept printing the warning:

 tipc: Too large msg, purging xmit list 1 5 0 40 4!
 tipc: Too large msg, purging xmit list 1 15 0 60 4!

And with tipc_link_entry.mtu 4294967228, a huge skb was allocated in
named_distribute(), and when purging it in tipc_link_xmit(), a crash
was even caused:

  general protection fault, probably for non-canonical address 0x2100001011000dd: 0000 [#1] PREEMPT SMP PTI
  CPU: 0 PID: 0 Comm: swapper/0 Kdump: loaded Not tainted 6.3.0.neta #19
  RIP: 0010:kfree_skb_list_reason+0x7e/0x1f0
  Call Trace:
   <IRQ>
   skb_release_data+0xf9/0x1d0
   kfree_skb_reason+0x40/0x100
   tipc_link_xmit+0x57a/0x740 [tipc]
   tipc_node_xmit+0x16c/0x5c0 [tipc]
   tipc_named_node_up+0x27f/0x2c0 [tipc]
   tipc_node_write_unlock+0x149/0x170 [tipc]
   tipc_rcv+0x608/0x740 [tipc]
   tipc_udp_recv+0xdc/0x1f0 [tipc]
   udp_queue_rcv_one_skb+0x33e/0x620
   udp_unicast_rcv_skb.isra.72+0x75/0x90
   __udp4_lib_rcv+0x56d/0xc20
   ip_protocol_deliver_rcu+0x100/0x2d0

This patch fixes it by checking the new mtu against tipc_bearer_min_mtu(),
and not updating mtu if it is too small.

Fixes: ed193ece2649 ("tipc: simplify link mtu negotiation")
Reported-by: Shuang Li <shuali@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/tipc/link.c b/net/tipc/link.c
index b3ce24823f50354c694da21f6c3dbad25f249294..2eff1c7949cbcc5f97855bb58373ec3595496aa0 100644 (file)
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -2200,7 +2200,7 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
        struct tipc_msg *hdr = buf_msg(skb);
        struct tipc_gap_ack_blks *ga = NULL;
        bool reply = msg_probe(hdr), retransmitted = false;
-       u32 dlen = msg_data_sz(hdr), glen = 0;
+       u32 dlen = msg_data_sz(hdr), glen = 0, msg_max;
        u16 peers_snd_nxt =  msg_next_sent(hdr);
        u16 peers_tol = msg_link_tolerance(hdr);
        u16 peers_prio = msg_linkprio(hdr);
@@ -2239,6 +2239,9 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
        switch (mtyp) {
        case RESET_MSG:
        case ACTIVATE_MSG:
+               msg_max = msg_max_pkt(hdr);
+               if (msg_max < tipc_bearer_min_mtu(l->net, l->bearer_id))
+                       break;
                /* Complete own link name with peer's interface name */
                if_name =  strrchr(l->name, ':') + 1;
                if (sizeof(l->name) - (if_name - l->name) <= TIPC_MAX_IF_NAME)
@@ -2283,8 +2286,8 @@ static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
                l->peer_session = msg_session(hdr);
                l->in_session = true;
                l->peer_bearer_id = msg_bearer_id(hdr);
-               if (l->mtu > msg_max_pkt(hdr))
-                       l->mtu = msg_max_pkt(hdr);
+               if (l->mtu > msg_max)
+                       l->mtu = msg_max;
                break;
 
        case STATE_MSG: