linux-kernel - Re: [PATCH] fib:fix BUG_ON in fib_nl

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Date:	Sun, 11 Sep 2011 09:12:35 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Wanlong Gao <wanlong.gao@...il.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	davem@...emloft.net, omarapazanadi@...il.com,
	Gao feng <gaofeng@...fujitsu.com>
Subject: Re: [PATCH] fib:fix BUG_ON in fib_nl_newrule when add new fib rule

Le dimanche 11 septembre 2011 à 01:19 +0800, Wanlong Gao a écrit :
> From: Gao feng <gaofeng@...fujitsu.com>
> 
> add new fib rule can cause BUG_ON
> the reproduce shell is
> 
> #ip rule add pref 38
> #ip rule add pref 38
> #ip rule add to 192.168.3.0/24 goto 38
> #ip rule del pref 38
> #ip rule add to 192.168.3.0/24 goto 38
> #ip rule add pref 38
> 
> then the BUG_ON will happen
> add a var unresolved in struct fib_rule
> and use it to identify whether this rule is unresolved
> 
> Signed-off-by: Gao feng <gaofeng@...fujitsu.com>
> ---
>  include/net/fib_rules.h |    1 +
>  net/core/fib_rules.c    |    5 ++++-
>  2 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/include/net/fib_rules.h b/include/net/fib_rules.h
> index 075f1e3..e4bae01 100644
> --- a/include/net/fib_rules.h
> +++ b/include/net/fib_rules.h
> @@ -19,6 +19,7 @@ struct fib_rule {
>  	u32			flags;
>  	u32			table;
>  	u8			action;
> +	u8			unresolved;
>  	u32			target;
>  	struct fib_rule __rcu	*ctarget;
>  	char			iifname[IFNAMSIZ];
> diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
> index e7ab0c0..aa20560 100644
> --- a/net/core/fib_rules.c
> +++ b/net/core/fib_rules.c
> @@ -384,9 +384,11 @@ static int fib_nl_newrule(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
>  		 */
>  		list_for_each_entry(r, &ops->rules_list, list) {
>  			if (r->action == FR_ACT_GOTO &&
> -			    r->target == rule->pref) {
> +			    r->target == rule->pref &&
> +			    r->unresolved) {
>  				BUG_ON(rtnl_dereference(r->ctarget) != NULL);
>  				rcu_assign_pointer(r->ctarget, rule);
> +				r->unresolved = 0;
>  				if (--ops->unresolved_rules == 0)
>  					break;
>  			}
> @@ -488,6 +490,7 @@ static int fib_nl_delrule(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
>  			list_for_each_entry(tmp, &ops->rules_list, list) {
>  				if (rtnl_dereference(tmp->ctarget) == rule) {
>  					rcu_assign_pointer(tmp->ctarget, NULL);
> +					tmp->unresolved = 1;
>  					ops->unresolved_rules++;
>  				}
>  			}

Hmm, good catch, but you add 'unresolved' field but dont init it
correctly to 1 in all cases.

Following will break :

ip rule add pref 100
ip rule add to 192.168.3.0/24 goto 200
ip rule add pref 200

Normally, we should have 

unresolved = (ctarget == NULL);

What about following patch instead ?

diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index e7ab0c0..3231b46 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -384,8 +384,8 @@ static int fib_nl_newrule(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
 		 */
 		list_for_each_entry(r, &ops->rules_list, list) {
 			if (r->action == FR_ACT_GOTO &&
-			    r->target == rule->pref) {
-				BUG_ON(rtnl_dereference(r->ctarget) != NULL);
+			    r->target == rule->pref &&
+			    rtnl_dereference(r->ctarget) == NULL) {
 				rcu_assign_pointer(r->ctarget, rule);
 				if (--ops->unresolved_rules == 0)
 					break;


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