Re: [BUG ?] ipv6: addrconf: Adds a missing in6_ifa_hold()

[David Ahern <dsahern@gmail.com>]

On 10/30/17 9:53 PM, Eric Dumazet wrote:
> David, I was looking at addrconf_permanent_addr() and wondered
> if there is not some problem with it.
> 
> It seems we need to increment ifp refcount before calling
> ipv6_del_addr()
> 
> Could you double check if this patch is needed, I am guessing you have a
> test suite exercising this code path ?

A lot has changed in 20 months since the patch that added the code. For
instance, taking down the 'lo' device no longer affects host routes on
other interfaces. Also, fixup_permanent_addr only fails on memory
allocation. Did you hit this with a test case because I do not have a
general one that causes the memory failure (hard coding a failure for an
address is the only way).

> 
> Thanks.
> 
> PS : Presumably CONFIG_REFCOUNT_FULL=y should have warned you of the
> problem.

I have not run a debug kernel in a while -- and did not have this option
set. Added it to my debug config.

> 
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 4a96ebbf8eda5f59a6ff88e836d666a404d2bf0d..8a1c846d3df949a4638589f187120db22a3525ba 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -3335,6 +3335,7 @@ static void addrconf_permanent_addr(struct net_device *dev)
>  		if ((ifp->flags & IFA_F_PERMANENT) &&
>  		    fixup_permanent_addr(idev, ifp) < 0) {
>  			write_unlock_bh(&idev->lock);
> +			in6_ifa_hold(ifp);
>  			ipv6_del_addr(ifp);
>  			write_lock_bh(&idev->lock);
>  

Yes, forcing a failure here does trigger refcnt warning, but then you
knew that. ;-)


PS. is the following a known failure? I triggered it looking into your
report

[  170.385741] ======================================================
[  170.387490] WARNING: possible circular locking dependency detected
[  170.389214] 4.14.0-rc5+ #338 Not tainted
[  170.390323] ------------------------------------------------------
[  170.392017] swapper/0/0 is trying to acquire lock:
[  170.393408]  (slock-AF_INET){+.-.}, at: [<ffffffff8172848b>]
tcp_delack_timer+0x29/0xb1
[  170.395622]
but task is already holding lock:
[  170.396943]  ((timer)){+.-.}, at: [<ffffffff810f3c53>]
call_timer_fn+0x5/0x36b
[  170.397912]
which lock already depends on the new lock.

[  170.398986]
the existing dependency chain (in reverse order) is:
[  170.399965]
-> #1 ((timer)){+.-.}:
[  170.400629]        lock_acquire+0x154/0x220
[  170.401198]        del_timer_sync+0x47/0xbd
[  170.401760]        inet_csk_reqsk_queue_drop+0x109/0x141
[  170.402464]        inet_csk_complete_hashdance+0x3b/0x68
[  170.403173]        tcp_check_req+0x517/0x5f1
[  170.403746]        tcp_v4_rcv+0x6ad/0xce7
[  170.404287]        ip_local_deliver_finish+0x1d4/0x281
[  170.404985]        ip_local_deliver+0xaf/0xcf
[  170.405571]        ip_rcv_finish+0x632/0x6ff
[  170.406140]        ip_rcv+0x45d/0x4a6
...