netdev - Re: [PATCH ipsec 7/7] xfrm: policy: fix infinite loop when merging src-nodes

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Date:   Fri, 4 Jan 2019 20:49:48 -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 7/7] xfrm: policy: fix infinite loop when merging src-nodes

On Fri, Jan 4, 2019 at 5:19 AM Florian Westphal <fw@...len.de> wrote:
>
> With very small change to test script we can trigger softlockup due to
> bogus assignment of 'p' (policy to be examined) on restart.
>
> Previously the two to-be-merged nodes had same address/prefixlength pair,
> so no erase/reinsert was necessary, we only had to append the list from
> node a to b.
>
> If prefix lengths are different, the node has to be deleted and re-inserted
> into the tree, with the updated prefix length.  This was broken; due to
> bogus update to 'p' this loops forever.
>
> Add a 'restart' label and use that instead.
>
> While at it, don't perform the unneeded reinserts of the policies that
> are already sorted into the 'new' node.
>
> A previous patch in this series made xfrm_policy_inexact_list_reinsert()
> use the relative position indicator to sort policies according to age in
> case priorities are identical.
>
> Fixes: 6ac098b2a9d30 ("xfrm: policy: add 2nd-level saddr trees for inexact policies")
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---
>  net/xfrm/xfrm_policy.c                     | 15 +++++++--------
>  tools/testing/selftests/net/xfrm_policy.sh |  4 ++--
>  2 files changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index e691683223ee..8cfd75b62396 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -886,12 +886,13 @@ static void xfrm_policy_inexact_node_reinsert(struct net *net,
>                                               struct rb_root *new,
>                                               u16 family)
>  {
> -       struct rb_node **p, *parent = NULL;
>         struct xfrm_pol_inexact_node *node;
> +       struct rb_node **p, *parent;
>
>         /* we should not have another subtree here */
>         WARN_ON_ONCE(!RB_EMPTY_ROOT(&n->root));
> -
> +restart:
> +       parent = NULL;
>         p = &new->rb_node;
>         while (*p) {
>                 u8 prefixlen;
> @@ -911,12 +912,11 @@ static void xfrm_policy_inexact_node_reinsert(struct net *net,
>                 } else {
>                         struct xfrm_policy *tmp;
>
> -                       hlist_for_each_entry(tmp, &node->hhead, bydst)
> -                               tmp->bydst_reinsert = true;
> -                       hlist_for_each_entry(tmp, &n->hhead, bydst)
> +                       hlist_for_each_entry(tmp, &n->hhead, bydst) {


hlist_for_each_entry_safe()?


>                                 tmp->bydst_reinsert = true;
> +                               hlist_del_rcu(&tmp->bydst);
> +                       }
>
> -                       INIT_HLIST_HEAD(&node->hhead);
>                         xfrm_policy_inexact_list_reinsert(net, node, family);
>
>                         if (node->prefixlen == n->prefixlen) {
> @@ -928,8 +928,7 @@ static void xfrm_policy_inexact_node_reinsert(struct net *net,
>                         kfree_rcu(n, rcu);
>                         n = node;
>                         n->prefixlen = prefixlen;
> -                       *p = new->rb_node;
> -                       parent = NULL;
> +                       goto restart;
>                 }
>         }
>
> diff --git a/tools/testing/selftests/net/xfrm_policy.sh b/tools/testing/selftests/net/xfrm_policy.sh
> index 8ce54600d4d1..71d7fdc513c1 100755
> --- a/tools/testing/selftests/net/xfrm_policy.sh
> +++ b/tools/testing/selftests/net/xfrm_policy.sh
> @@ -78,8 +78,8 @@ do_overlap()
>      # adds a new node in the 10.0.0.0/24 tree (dst node exists).
>      ip -net $ns xfrm policy add src 10.2.0.0/24 dst 10.0.0.0/24 dir fwd priority 200 action block
>
> -    # adds a 10.2.0.0/24 node, but for different dst.
> -    ip -net $ns xfrm policy add src 10.2.0.0/24 dst 10.0.1.0/24 dir fwd priority 200 action block
> +    # adds a 10.2.0.0/23 node, but for different dst.
> +    ip -net $ns xfrm policy add src 10.2.0.0/23 dst 10.0.1.0/24 dir fwd priority 200 action block
>
>      # dst now overlaps with the 10.0.1.0/24 ESP policy in fwd.
>      # kernel must 'promote' existing one (10.0.0.0/24) to 10.0.0.0/23.
> --
> 2.19.2
>