Re: [Patch net] tipc: switch to rhashtable iterator

[David Miller <davem@davemloft.net>]

From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Fri, 24 Aug 2018 12:28:06 -0700

> syzbot reported a use-after-free in tipc_group_fill_sock_diag(),
> where tipc_group_fill_sock_diag() still reads tsk->group meanwhile
> tipc_group_delete() just deletes it in tipc_release().
> 
> tipc_nl_sk_walk() aims to lock this sock when walking each sock
> in the hash table to close race conditions with sock changes like
> this one, by acquiring tsk->sk.sk_lock.slock spinlock, unfortunately
> this doesn't work at all. All non-BH call path should take
> lock_sock() instead to make it work.
> 
> tipc_nl_sk_walk() brutally iterates with raw rht_for_each_entry_rcu()
> where RCU read lock is required, this is the reason why lock_sock()
> can't be taken on this path. This could be resolved by switching to
> rhashtable iterator API's, where taking a sleepable lock is possible.
> Also, the iterator API's are friendly for restartable calls like
> diag dump, the last position is remembered behind the scence,
> all we need to do here is saving the iterator into cb->args[].
> 
> I tested this with parallel tipc diag dump and thousands of tipc
> socket creation and release, no crash or memory leak.
> 
> Reported-by: syzbot+b9c8f3ab2994b7cd1625@syzkaller.appspotmail.com
> Cc: Jon Maloy <jon.maloy@ericsson.com>
> Cc: Ying Xue <ying.xue@windriver.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

Applied and queued up for -stable, thanks Cong.