netdev - Re: [PATCH ipsec 4/7] xfrm: policy: delete inexact policies from inexact list on hash rebuild

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Date:   Fri, 4 Jan 2019 20:46:44 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Steffen Klassert <steffen.klassert@...unet.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH ipsec 4/7] xfrm: policy: delete inexact policies from
 inexact list on hash rebuild

On Fri, Jan 4, 2019 at 5:19 AM Florian Westphal <fw@...len.de> wrote:
>
> An xfrm hash rebuild has to reset the inexact policy list before the
> policies get re-inserted: A change of hash thresholds will result in
> policies to get moved from inexact tree to the policy hash table.
>
> If the thresholds are increased again later, they get moved from hash
> table to inexact tree.
>
> We must unlink all policies from the inexact tree before re-insertion.
>
> Otherwise 'migrate' may find policies that are in main hash table a
> second time, when it searches the inexact lists.
>
> Furthermore, re-insertion without deletion can cause elements ->next to
> point back to itself, causing soft lockups or double-frees.
>
> Reported-by: syzbot+9d971dd21eb26567036b@...kaller.appspotmail.com
> Fixes: 9cf545ebd591da ("xfrm: policy: store inexact policies in a tree ordered by destination address")
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---
>  net/xfrm/xfrm_policy.c | 23 ++++++++++-------------
>  1 file changed, 10 insertions(+), 13 deletions(-)
>
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index d8fba27a4bfb..24dfd1e47cf0 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -680,16 +680,6 @@ static void xfrm_hash_resize(struct work_struct *work)
>         mutex_unlock(&hash_resize_mutex);
>  }
>
> -static void xfrm_hash_reset_inexact_table(struct net *net)
> -{
> -       struct xfrm_pol_inexact_bin *b;
> -
> -       lockdep_assert_held(&net->xfrm.xfrm_policy_lock);
> -
> -       list_for_each_entry(b, &net->xfrm.inexact_bins, inexact_bins)
> -               INIT_HLIST_HEAD(&b->hhead);
> -}
> -
>  /* Make sure *pol can be inserted into fastbin.
>   * Useful to check that later insert requests will be sucessful
>   * (provided xfrm_policy_lock is held throughout).
> @@ -1279,10 +1269,14 @@ static void xfrm_hash_rebuild(struct work_struct *work)
>         }
>
>         /* reset the bydst and inexact table in all directions */


Does this comment need to update?


> -       xfrm_hash_reset_inexact_table(net);
> -
>         for (dir = 0; dir < XFRM_POLICY_MAX; dir++) {
> -               INIT_HLIST_HEAD(&net->xfrm.policy_inexact[dir]);
> +               struct hlist_node *n;
> +
> +               hlist_for_each_entry_safe(policy, n,
> +                                         &net->xfrm.policy_inexact[dir],
> +                                         bydst_inexact_list)
> +                       hlist_del_init(&policy->bydst_inexact_list);
> +
>                 hmask = net->xfrm.policy_bydst[dir].hmask;
>                 odst = net->xfrm.policy_bydst[dir].table;
>                 for (i = hmask; i >= 0; i--)
> @@ -1314,6 +1308,9 @@ static void xfrm_hash_rebuild(struct work_struct *work)
>                 newpos = NULL;
>                 chain = policy_hash_bysel(net, &policy->selector,
>                                           policy->family, dir);
> +
> +               hlist_del_rcu(&policy->bydst);


Need to test hlist_unhashed()?


> +
>                 if (!chain) {
>                         void *p = xfrm_policy_inexact_insert(policy, dir, 0);
>
> --
> 2.19.2
>