Re: [PATCH net] sctp: do not peel off an assoc from one netns to another one

[David Miller <davem@davemloft.net>]

From: Xin Long <lucien.xin@gmail.com>
Date: Tue, 17 Oct 2017 23:26:10 +0800

> Now when peeling off an association to the sock in another netns, all
> transports in this assoc are not to be rehashed and keep use the old
> key in hashtable.
> 
> As a transport uses sk->net as the hash key to insert into hashtable,
> it would miss removing these transports from hashtable due to the new
> netns when closing the sock and all transports are being freeed, then
> later an use-after-free issue could be caused when looking up an asoc
> and dereferencing those transports.
> 
> This is a very old issue since very beginning, ChunYu found it with
> syzkaller fuzz testing with this series:
> 
>   socket$inet6_sctp()
>   bind$inet6()
>   sendto$inet6()
>   unshare(0x40000000)
>   getsockopt$inet_sctp6_SCTP_GET_ASSOC_ID_LIST()
>   getsockopt$inet_sctp6_SCTP_SOCKOPT_PEELOFF()
> 
> This patch is to block this call when peeling one assoc off from one
> netns to another one, so that the netns of all transport would not
> go out-sync with the key in hashtable.
> 
> Note that this patch didn't fix it by rehashing transports, as it's
> difficult to handle the situation when the tuple is already in use
> in the new netns. Besides, no one would like to peel off one assoc
> to another netns, considering ipaddrs, ifaces, etc. are usually
> different.
> 
> Reported-by: ChunYu Wang <chunwang@redhat.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied.