netdev - Re: [PATCH net] ipv6: mcast: fix a use-after-free in inet6_mc

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Date:   Mon, 15 Oct 2018 22:39:43 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net] ipv6: mcast: fix a use-after-free in inet6_mc_check

From: Eric Dumazet <edumazet@...gle.com>
Date: Fri, 12 Oct 2018 18:58:53 -0700

> syzbot found a use-after-free in inet6_mc_check [1]
> 
> The problem here is that inet6_mc_check() uses rcu
> and read_lock(&iml->sflock)
> 
> So the fact that ip6_mc_leave_src() is called under RTNL
> and the socket lock does not help us, we need to acquire
> iml->sflock in write mode.
> 
> In the future, we should convert all this stuff to RCU.
> 
> [1]
> BUG: KASAN: use-after-free in ipv6_addr_equal include/net/ipv6.h:521 [inline]
> BUG: KASAN: use-after-free in inet6_mc_check+0xae7/0xb40 net/ipv6/mcast.c:649
> Read of size 8 at addr ffff8801ce7f2510 by task syz-executor0/22432
 ...
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied and queued up for -stable, thanks.