linux-kernel - Re: net/xfrm: stack out-of-bounds in xfrm_flowi

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Date:   Tue, 14 Feb 2017 09:41:35 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/xfrm: stack out-of-bounds in xfrm_flowi_sport

On Tue, Feb 14, 2017 at 8:08 AM, Steffen Klassert
<steffen.klassert@...unet.com> wrote:
> On Mon, Feb 13, 2017 at 03:46:56PM +0100, Dmitry Vyukov wrote:
>>
>> On commit 7089db84e356562f8ba737c29e472cc42d530dbc.
>>
>>
>> struct flowi4 fl4_stack allocated on stack in udp_sendmsg is being
>> casted to larger struct flowi and then accessed.
>
> Looks like the problem is when using IPv4-mapped IPv6 addresses.
>
> Does the patch below help?


Steffen, can you please run the reproducer I provided?
I specifically spent time to supply you with a simple, reliable
reproducer. I am not even saying about adding a test case for the bug.
Kernel development practices seem to encourage developers to not
bother with tests. But at least testing a patch that you are sending
looks like a reasonable thing to do.
Thanks


> Subject: [PATCH RFC ipsec] xfrm: Don't use sk_family for socket policy lookups
>
> On IPv4-mapped IPv6 addresses sk_family is AF_INET6,
> but the flow informations are created based on AF_INET.
> So the routing set up 'struct flowi4' but we try to
> access 'struct flowi6' what leads to an out of bounds
> access. Fix this by using the family we get with the
> dst_entry, like we do it for the standard policy lookup.
>
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
> ---
>  net/xfrm/xfrm_policy.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index b5e665b..4891b7b 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -1216,7 +1216,7 @@ static inline int policy_to_flow_dir(int dir)
>  }
>
>  static struct xfrm_policy *xfrm_sk_policy_lookup(const struct sock *sk, int dir,
> -                                                const struct flowi *fl)
> +                                                const struct flowi *fl, u16 family)
>  {
>         struct xfrm_policy *pol;
>         struct net *net = sock_net(sk);
> @@ -1225,8 +1225,7 @@ static struct xfrm_policy *xfrm_sk_policy_lookup(const struct sock *sk, int dir,
>         read_lock_bh(&net->xfrm.xfrm_policy_lock);
>         pol = rcu_dereference(sk->sk_policy[dir]);
>         if (pol != NULL) {
> -               bool match = xfrm_selector_match(&pol->selector, fl,
> -                                                sk->sk_family);
> +               bool match = xfrm_selector_match(&pol->selector, fl, family);
>                 int err = 0;
>
>                 if (match) {
> @@ -2221,7 +2220,7 @@ struct dst_entry *xfrm_lookup(struct net *net, struct dst_entry *dst_orig,
>         sk = sk_const_to_full_sk(sk);
>         if (sk && sk->sk_policy[XFRM_POLICY_OUT]) {
>                 num_pols = 1;
> -               pols[0] = xfrm_sk_policy_lookup(sk, XFRM_POLICY_OUT, fl);
> +               pols[0] = xfrm_sk_policy_lookup(sk, XFRM_POLICY_OUT, fl, family);
>                 err = xfrm_expand_policies(fl, family, pols,
>                                            &num_pols, &num_xfrms);
>                 if (err < 0)
> @@ -2500,7 +2499,7 @@ int __xfrm_policy_check(struct sock *sk, int dir, struct sk_buff *skb,
>         pol = NULL;
>         sk = sk_to_full_sk(sk);
>         if (sk && sk->sk_policy[dir]) {
> -               pol = xfrm_sk_policy_lookup(sk, dir, &fl);
> +               pol = xfrm_sk_policy_lookup(sk, dir, &fl, family);
>                 if (IS_ERR(pol)) {
>                         XFRM_INC_STATS(net, LINUX_MIB_XFRMINPOLERROR);
>                         return 0;
> --
> 1.9.1
>