linux-kernel - Re: net: heap out-of-bounds in fib6_clean_node/rt6_fill_node/fib6_age/fib6_prune

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Date:   Tue, 7 Mar 2017 10:57:53 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net: heap out-of-bounds in
 fib6_clean_node/rt6_fill_node/fib6_age/fib6_prune_clone

On 3/7/17 1:43 AM, Dmitry Vyukov wrote:
> This is on c1ae3cfa0e89fa1a7ecc4c99031f5e9ae99d9201. No other kernel
> output from your patch (pr_err).
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 30179 at net/ipv6/ip6_fib.c:158
> rt6_rcu_free+0x61/0x70 net/ipv6/ip6_fib.c:158
> Kernel panic - not syncing: panic_on_warn set ...

you have panic_on_warn set ...

> 
> CPU: 1 PID: 30179 Comm: syz-executor3 Not tainted 4.11.0-rc1+ #310
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:16 [inline]
>  dump_stack+0x2fb/0x3fd lib/dump_stack.c:52
>  panic+0x20f/0x426 kernel/panic.c:180
>  __warn+0x1c4/0x1e0 kernel/panic.c:541
>  warn_slowpath_null+0x2c/0x40 kernel/panic.c:584
>  rt6_rcu_free+0x61/0x70 net/ipv6/ip6_fib.c:158

and this is my WARN_ON in rt6_rcu_free which is showing an additional
change is needed

>  rt6_release+0x1ee/0x290 net/ipv6/ip6_fib.c:189
>  fib6_add_rt2node net/ipv6/ip6_fib.c:922 [inline]

in fib6_add_rt2node for the route replace path (whitespace damaged on
the copy-paste):

@@ -916,6 +919,7 @@ static int fib6_add_rt2node(struct fib6_node *fn,
struct rt6_info *rt,
                }
                nsiblings = iter->rt6i_nsiblings;
                fib6_purge_rt(iter, fn, info->nl_net);
+               iter->dst.flags &= ~DST_IN_FIB;
                rt6_release(iter);

                if (nsiblings) {
@@ -926,6 +930,7 @@ static int fib6_add_rt2node(struct fib6_node *fn,
struct rt6_info *rt,
                                if (rt6_qualify_for_ecmp(iter)) {
                                        *ins = iter->dst.rt6_next;
                                        fib6_purge_rt(iter, fn,
info->nl_net);
+                                       iter->dst.flags &= ~DST_IN_FIB;
                                        rt6_release(iter);
                                        nsiblings--;
                                } else {