> -----Original Message----- > From: Mark Bloch <[email protected]> > Sent: Thursday, May 07, 2020 3:36 PM > To: Divya Indi <[email protected]>; [email protected]; linux- > [email protected]; Jason Gunthorpe <[email protected]>; Wan, Kaike > <[email protected]> > Cc: Gerd Rausch <[email protected]>; Håkon Bugge > <[email protected]>; Srinivas Eeda <[email protected]>; > Rama Nichanamatlu <[email protected]>; Doug Ledford > <[email protected]> > Subject: Re: [PATCH 1/2] IB/sa: Resolving use-after-free in ib_nl_send_msg. > > > > @@ -1123,6 +1156,18 @@ int ib_nl_handle_resolve_resp(struct sk_buff > > *skb, > > > > send_buf = query->mad_buf; > > > > + /* > > + * Make sure the IB_SA_NL_QUERY_SENT flag is set before > > + * processing this query. If flag is not set, query can be accessed in > > + * another context while setting the flag and processing the query > will > > + * eventually release it causing a possible use-after-free. > > + */ > > + if (unlikely(!ib_sa_nl_query_sent(query))) { > > Can't there be a race here where you check the flag (it isn't set) and before > you call wait_event() the flag is set and wake_up() is called which means you > will wait here forever?
Should wait_event() catch that? That is, if the flag is not set, wait_event() will sleep until the flag is set. or worse, a timeout will happen the query will be > freed and them some other query will call wake_up() and we have again a > use-after-free. The request has been deleted from the request list by this time and therefore the timeout should have no impact here. > > > + spin_unlock_irqrestore(&ib_nl_request_lock, flags); > > + wait_event(wait_queue, ib_sa_nl_query_sent(query)); > > What if there are two queries sent to userspace, shouldn't you check and > make sure you got woken up by the right one setting the flag? The wait_event() is conditioned on the specific query (ib_sa_nl_query_sent(query)), not on the wait_queue itself. > > Other than that, the entire solution makes it very complicated to reason with > (flags set/checked without locking etc) maybe we should just revert and fix it > the other way? The flag could certainly be set under the lock, which may reduce complications. Kaike
