Re: [tipc-discussion] [PATCHv2 net 2/3] tipc: do not update mtu if msg_max is too small in mtu negotiation

[Jon M. <jm...@re...>]

On 2023-05-03 09:35, Xin Long wrote:
> On Tue, May 2, 2023 at 11:31 PM Tung Quang Nguyen
> <tun...@de...> 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/201...@da.../
>
> unless there are some new rules I missed.
I have not seen this one before, and I disagree with David here. Many of 
the changes
between versions are trivial, and some comments even incomprehensible 
once the patch has
been applied.
I have always put them after the "---" comment, and I will continue to 
do so until David starts
rejecting such patches.

But ok, do as you find right.

///jon

>
> Thanks.
>
>>> Fixes: ed193ece2649 ("tipc: simplify link mtu negotiation")
>>> Reported-by: Shuang Li <sh...@re...>
>>> Signed-off-by: Xin Long <luc...@gm...>
>>> ---
>>> 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