>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 "---".
>
>Fixes: ed193ece2649 ("tipc: simplify link mtu negotiation")
>Reported-by: Shuang Li <shu...@redhat.com>
>Signed-off-by: Xin Long <lucien....@gmail.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
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