Re: [PATCH v2] net: tipc: fix possible infoleak in tipc_mon_rcv()

[Jakub Kicinski]

On Thu, 30 Jun 2022 17:19:21 +0800 Hangyu Hua wrote:
> On 2022/6/30 11:31, Jakub Kicinski wrote:
> > On Tue, 28 Jun 2022 16:31:22 +0800 Hangyu Hua wrote:  
> >> dom_bef is use to cache current domain record only if current domain
> >> exists. But when current domain does not exist, dom_bef will still be used
> >> in mon_identify_lost_members. This may lead to an information leak.  
> > 
> > AFAICT applied_bef must be zero if peer->domain was 0, so I don't think
> > mon_identify_lost_members() will do anything.
> >   
> 
> void tipc_mon_rcv(struct net *net, void *data, u16 dlen, u32 addr,
> 		  struct tipc_mon_state *state, int bearer_id)
> {
> ...
> 	if (!dom || (dom->len < new_dlen)) {
> 		kfree(dom);
> 		dom = kmalloc(new_dlen, GFP_ATOMIC);	<--- [1]
> 		peer->domain = dom;
> 		if (!dom)
> 			goto exit;
> 	}
> ...
> }
> 
> peer->domain will be NULL when [1] fails. But there will not change 
> peer->applied to 0. In this case, if tipc_mon_rcv is called again then 
> an information leak will happen.

I see, good analysis! Jon, Xue - is there a reason domain gets wiped
on memory allocation failure? I'd think we should leave the previous
pointer in place instead of freeing it first.