netdev - Re: [PATCHv2 net 2/3] tipc: do not update mtu if msg

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Date: Wed, 3 May 2023 09:35:02 -0400
From: Xin Long <lucien.xin@...il.com>
To: Tung Quang Nguyen <tung.q.nguyen@...tech.com.au>
Cc: network dev <netdev@...r.kernel.org>, 
	"tipc-discussion@...ts.sourceforge.net" <tipc-discussion@...ts.sourceforge.net>, 
	"davem@...emloft.net" <davem@...emloft.net>, "kuba@...nel.org" <kuba@...nel.org>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Jon Maloy <jmaloy@...hat.com>
Subject: Re: [PATCHv2 net 2/3] tipc: do not update mtu if msg_max is too small
 in mtu negotiation

On Tue, May 2, 2023 at 11:31 PM Tung Quang Nguyen
<tung.q.nguyen@...tech.com.au> wrote:
>
> >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.
> >
> >v1->v2:
> >  - do the msg_max check against the min MTU early, as Tung suggested.
> Please move above version change comment to after "---".
I think it's correct to NOT use ''---' for version changes, see the
comment from davem:

  https://lore.kernel.org/netdev/20160415.172858.253625178036493951.davem@davemloft.net/

unless there are some new rules I missed.

Thanks.

> >
> >Fixes: ed193ece2649 ("tipc: simplify link mtu negotiation")
> >Reported-by: Shuang Li <shuali@...hat.com>
> >Signed-off-by: Xin Long <lucien.xin@...il.com>
> >---
> > net/tipc/link.c | 9 ++++++---
> > 1 file changed, 6 insertions(+), 3 deletions(-)
> >
> >diff --git a/net/tipc/link.c b/net/tipc/link.c
> >index b3ce24823f50..2eff1c7949cb 100644
> >--- 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:
> >--
> >2.39.1
>