netdev - Re: [PATCH] ipv6: do not free rt if FIB_LOOKUP

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Date:   Tue, 24 Sep 2019 11:35:54 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, Wei Wang <weiwan@...gle.com>
Subject: Re: [PATCH] ipv6: do not free rt if FIB_LOOKUP_NOREF is set on
 suppress rule

Hey Wei,

I meant to CC you but slipped up. Sorry about that. Take a look at
this thread if you have a chance.

Thanks,
Jason

On Tue, Sep 24, 2019 at 10:03 AM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> Commit 7d9e5f422150 removed references from certain dsts, but accounting
> for this never translated down into the fib6 suppression code. This bug
> was triggered by WireGuard users who use wg-quick(8), which uses the
> "suppress-prefix" directive to ip-rule(8) for routing all of their
> internet traffic without routing loops. The test case in the link of
> this commit reliably triggers various crashes due to the use-after-free
> caused by the reference underflow.
>
> Cc: stable@...r.kernel.org
> Fixes: 7d9e5f422150 ("ipv6: convert major tx path to use RT6_LOOKUP_F_DST_NOREF")
> Test-case: https://git.zx2c4.com/WireGuard/commit/?id=ad66532000f7a20b149e47c5eb3a957362c8e161
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  net/ipv6/fib6_rules.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv6/fib6_rules.c b/net/ipv6/fib6_rules.c
> index d22b6c140f23..f9e8fe3ff0c5 100644
> --- a/net/ipv6/fib6_rules.c
> +++ b/net/ipv6/fib6_rules.c
> @@ -287,7 +287,8 @@ static bool fib6_rule_suppress(struct fib_rule *rule, struct fib_lookup_arg *arg
>         return false;
>
>  suppress_route:
> -       ip6_rt_put(rt);
> +       if (!(arg->flags & FIB_LOOKUP_NOREF))
> +               ip6_rt_put(rt);
>         return true;
>  }
>
> --
> 2.21.0

On Tue, Sep 24, 2019 at 10:03 AM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> Commit 7d9e5f422150 removed references from certain dsts, but accounting
> for this never translated down into the fib6 suppression code. This bug
> was triggered by WireGuard users who use wg-quick(8), which uses the
> "suppress-prefix" directive to ip-rule(8) for routing all of their
> internet traffic without routing loops. The test case in the link of
> this commit reliably triggers various crashes due to the use-after-free
> caused by the reference underflow.
>
> Cc: stable@...r.kernel.org
> Fixes: 7d9e5f422150 ("ipv6: convert major tx path to use RT6_LOOKUP_F_DST_NOREF")
> Test-case: https://git.zx2c4.com/WireGuard/commit/?id=ad66532000f7a20b149e47c5eb3a957362c8e161
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  net/ipv6/fib6_rules.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv6/fib6_rules.c b/net/ipv6/fib6_rules.c
> index d22b6c140f23..f9e8fe3ff0c5 100644
> --- a/net/ipv6/fib6_rules.c
> +++ b/net/ipv6/fib6_rules.c
> @@ -287,7 +287,8 @@ static bool fib6_rule_suppress(struct fib_rule *rule, struct fib_lookup_arg *arg
>         return false;
>
>  suppress_route:
> -       ip6_rt_put(rt);
> +       if (!(arg->flags & FIB_LOOKUP_NOREF))
> +               ip6_rt_put(rt);
>         return true;
>  }
>
> --
> 2.21.0



-- 
Jason A. Donenfeld
Deep Space Explorer
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