[Patch net] ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

[Patch net] ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

[Cong Wang]

Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
-> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
because ip6_null_entry is returned in this path since ip6_null_entry
is kinda default for a ipv6 route table root node. Quote from
David Ahern:

 ip6_null_entry is the root of all ipv6 fib tables making it integrated
 into the table ...

We should ignore any attempt of trying to delete it, like we do in
__ip6_del_rt() path and several others.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/ipv6/route.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f54f426..9da77e9 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
 static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 {
 	struct nl_info *info = &cfg->fc_nlinfo;
+	struct net *net = info->nl_net;
 	struct sk_buff *skb = NULL;
 	struct fib6_table *table;
 	int err;
 
+	if (rt == net->ipv6.ip6_null_entry)
+		return -ENOENT;
 	table = rt->rt6i_table;
 	write_lock_bh(&table->tb6_lock);
 
@@ -2184,7 +2187,7 @@ static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 		if (skb) {
 			u32 seq = info->nlh ? info->nlh->nlmsg_seq : 0;
 
-			if (rt6_fill_node(info->nl_net, skb, rt,
+			if (rt6_fill_node(net, skb, rt,
 					  NULL, NULL, 0, RTM_DELROUTE,
 					  info->portid, seq, 0) < 0) {
 				kfree_skb(skb);
@@ -2208,7 +2211,7 @@ static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 	ip6_rt_put(rt);
 
 	if (skb) {
-		rtnl_notify(skb, info->nl_net, info->portid, RTNLGRP_IPV6_ROUTE,
+		rtnl_notify(skb, net, info->portid, RTNLGRP_IPV6_ROUTE,
 			    info->nlh, gfp_any());
 	}
 	return err;
-- 
2.5.5

Re: [Patch net] ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

[Eric Dumazet]

On Mon, 2017-02-27 at 11:07 -0800, Cong Wang wrote:
> Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
> -> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
> because ip6_null_entry is returned in this path since ip6_null_entry
> is kinda default for a ipv6 route table root node. Quote from
> David Ahern:
> 
>  ip6_null_entry is the root of all ipv6 fib tables making it integrated
>  into the table ...
> 
> We should ignore any attempt of trying to delete it, like we do in
> __ip6_del_rt() path and several others.
> 
> Reported-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> ---
>  net/ipv6/route.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index f54f426..9da77e9 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
>  static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
>  {
>  	struct nl_info *info = &cfg->fc_nlinfo;
> +	struct net *net = info->nl_net;
>  	struct sk_buff *skb = NULL;
>  	struct fib6_table *table;
>  	int err;
>  
> +	if (rt == net->ipv6.ip6_null_entry)
> +		return -ENOENT;

It looks the caller did a dst_hold(&rt->dst);

So this new error path would leave a refcount leak.

Note that I was not able to trigger the crash on old kernels, so it
would be nice to get a precise idea of bug origin.

Thanks.

Re: [Patch net] ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

[Cong Wang]

On Mon, Feb 27, 2017 at 12:34 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Mon, 2017-02-27 at 11:07 -0800, Cong Wang wrote:
>> Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
>> -> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
>> because ip6_null_entry is returned in this path since ip6_null_entry
>> is kinda default for a ipv6 route table root node. Quote from
>> David Ahern:
>>
>>  ip6_null_entry is the root of all ipv6 fib tables making it integrated
>>  into the table ...
>>
>> We should ignore any attempt of trying to delete it, like we do in
>> __ip6_del_rt() path and several others.
>>
>> Reported-by: Andrey Konovalov <andreyknvl@google.com>
>> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
>> ---
>>  net/ipv6/route.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>> index f54f426..9da77e9 100644
>> --- a/net/ipv6/route.c
>> +++ b/net/ipv6/route.c
>> @@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
>>  static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
>>  {
>>       struct nl_info *info = &cfg->fc_nlinfo;
>> +     struct net *net = info->nl_net;
>>       struct sk_buff *skb = NULL;
>>       struct fib6_table *table;
>>       int err;
>>
>> +     if (rt == net->ipv6.ip6_null_entry)
>> +             return -ENOENT;
>
> It looks the caller did a dst_hold(&rt->dst);
>
> So this new error path would leave a refcount leak.

Interesting, this error path is not new for __ip6_del_rt_siblings()
so the leak was already there before mine, but you are probably
right we have a leak here.

I will send a separate patch to address this leak.

>
> Note that I was not able to trigger the crash on old kernels, so it
> would be nice to get a precise idea of bug origin.

Right, I miss:
Fixes: 0ae8133586ad ("net: ipv6: Allow shorthand delete of all
nexthops in multipath route")

Thanks!

Re: [Patch net] ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

[David Ahern]

On 2/27/17 12:34 PM, Eric Dumazet wrote:
> On Mon, 2017-02-27 at 11:07 -0800, Cong Wang wrote:
>> Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
>> -> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
>> because ip6_null_entry is returned in this path since ip6_null_entry
>> is kinda default for a ipv6 route table root node. Quote from
>> David Ahern:
>>
>>  ip6_null_entry is the root of all ipv6 fib tables making it integrated
>>  into the table ...
>>
>> We should ignore any attempt of trying to delete it, like we do in
>> __ip6_del_rt() path and several others.
>>
>> Reported-by: Andrey Konovalov <andreyknvl@google.com>
>> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
>> ---
>>  net/ipv6/route.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>> index f54f426..9da77e9 100644
>> --- a/net/ipv6/route.c
>> +++ b/net/ipv6/route.c
>> @@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
>>  static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
>>  {
>>  	struct nl_info *info = &cfg->fc_nlinfo;
>> +	struct net *net = info->nl_net;
>>  	struct sk_buff *skb = NULL;
>>  	struct fib6_table *table;
>>  	int err;
>>  
>> +	if (rt == net->ipv6.ip6_null_entry)
>> +		return -ENOENT;
> 
> It looks the caller did a dst_hold(&rt->dst);
> 
> So this new error path would leave a refcount leak.
> 
> Note that I was not able to trigger the crash on old kernels, so it
> would be nice to get a precise idea of bug origin.
> 

Cong: do you want to send a v2 catching the null entry in ip6_route_del
before the refcnt?

                for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
+                       /* do not allow deletion of the null route */
+                       if (rt == net->ipv6.ip6_null_entry)
+                               continue;

Fixes: 0ae8133586ad net: ipv6: Allow shorthand delete of all nexthops in
multipath route

Re: [Patch net] ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

[Cong Wang]

On Mon, Feb 27, 2017 at 1:00 PM, David Ahern <dsa@cumulusnetworks.com> wrote:
> On 2/27/17 12:34 PM, Eric Dumazet wrote:
>> On Mon, 2017-02-27 at 11:07 -0800, Cong Wang wrote:
>>> Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
>>> -> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
>>> because ip6_null_entry is returned in this path since ip6_null_entry
>>> is kinda default for a ipv6 route table root node. Quote from
>>> David Ahern:
>>>
>>>  ip6_null_entry is the root of all ipv6 fib tables making it integrated
>>>  into the table ...
>>>
>>> We should ignore any attempt of trying to delete it, like we do in
>>> __ip6_del_rt() path and several others.
>>>
>>> Reported-by: Andrey Konovalov <andreyknvl@google.com>
>>> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
>>> ---
>>>  net/ipv6/route.c | 7 +++++--
>>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
>>> index f54f426..9da77e9 100644
>>> --- a/net/ipv6/route.c
>>> +++ b/net/ipv6/route.c
>>> @@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
>>>  static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
>>>  {
>>>      struct nl_info *info = &cfg->fc_nlinfo;
>>> +    struct net *net = info->nl_net;
>>>      struct sk_buff *skb = NULL;
>>>      struct fib6_table *table;
>>>      int err;
>>>
>>> +    if (rt == net->ipv6.ip6_null_entry)
>>> +            return -ENOENT;
>>
>> It looks the caller did a dst_hold(&rt->dst);
>>
>> So this new error path would leave a refcount leak.
>>
>> Note that I was not able to trigger the crash on old kernels, so it
>> would be nice to get a precise idea of bug origin.
>>
>
> Cong: do you want to send a v2 catching the null entry in ip6_route_del
> before the refcnt?

Yeah, actually it is introduced by my patch because there is already
an ip6_rt_put() in __ip6_del_rt_siblings(). So v2 is coming...

>
>                 for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
> +                       /* do not allow deletion of the null route */
> +                       if (rt == net->ipv6.ip6_null_entry)
> +                               continue;
>
> Fixes: 0ae8133586ad net: ipv6: Allow shorthand delete of all nexthops in
> multipath route

Note, I moved the check into __ip6_del_rt_siblings() because __ip6_del_rt()
has a same check.

Re: [Patch net] ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

[David Ahern]

On 2/27/17 1:04 PM, Cong Wang wrote:
>>
>>                 for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
>> +                       /* do not allow deletion of the null route */
>> +                       if (rt == net->ipv6.ip6_null_entry)
>> +                               continue;
>>
>> Fixes: 0ae8133586ad net: ipv6: Allow shorthand delete of all nexthops in
>> multipath route
> 
> Note, I moved the check into __ip6_del_rt_siblings() because __ip6_del_rt()
> has a same check.
> 

that's b/c __ip6_del_rt has a second call path. __ip6_del_rt_siblings is
new and is not expecting to see the null entry. Catching it before the
dst_hold would be better.

Re: [Patch net] ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

[Cong Wang]

On Mon, Feb 27, 2017 at 1:06 PM, David Ahern <dsa@cumulusnetworks.com> wrote:
> On 2/27/17 1:04 PM, Cong Wang wrote:
>>>
>>>                 for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
>>> +                       /* do not allow deletion of the null route */
>>> +                       if (rt == net->ipv6.ip6_null_entry)
>>> +                               continue;
>>>
>>> Fixes: 0ae8133586ad net: ipv6: Allow shorthand delete of all nexthops in
>>> multipath route
>>
>> Note, I moved the check into __ip6_del_rt_siblings() because __ip6_del_rt()
>> has a same check.
>>
>
> that's b/c __ip6_del_rt has a second call path. __ip6_del_rt_siblings is
> new and is not expecting to see the null entry. Catching it before the
> dst_hold would be better.

Yeah, but it also depends on if we want to continue after the null entry,
at least __ip6_del_rt () returns an error for null entry, which looks more
correct than continuing to proceed after it.