Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Cong Wang]

(Cc'ing netfilter and Jamal)

On Sat, Aug 5, 2017 at 4:35 AM, Xin Long <lucien.xin@gmail.com> wrote:
> As we know in some target's checkentry it may dereference par.entryinfo
> to check entry stuff inside. But when sched action calls xt_check_target,
> par.entryinfo is set with NULL. It would cause kernel panic when calling
> some targets.
>
> It can be reproduce with:
>   # tc qd add dev eth1 ingress handle ffff:
>   # tc filter add dev eth1 parent ffff: u32 match u32 0 0 action xt \
>     -j ECN --ecn-tcp-remove
>
> It could also crash kernel when using target CLUSTERIP or TPROXY.
>
> By now there's no proper value for par.entryinfo in ipt_init_target,
> but it can not be set with NULL. This patch is to void all these
> panics by setting it with an ipt_entry obj with all members 0.
>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  net/sched/act_ipt.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/sched/act_ipt.c b/net/sched/act_ipt.c
> index 7c4816b..0f09f70 100644
> --- a/net/sched/act_ipt.c
> +++ b/net/sched/act_ipt.c
> @@ -41,6 +41,7 @@ static int ipt_init_target(struct net *net, struct xt_entry_target *t,
>  {
>         struct xt_tgchk_param par;
>         struct xt_target *target;
> +       struct ipt_entry e;
>         int ret = 0;
>
>         target = xt_request_find_target(AF_INET, t->u.user.name,
> @@ -48,10 +49,11 @@ static int ipt_init_target(struct net *net, struct xt_entry_target *t,
>         if (IS_ERR(target))
>                 return PTR_ERR(target);
>
> +       memset(&e, 0, sizeof(e));
>         t->u.kernel.target = target;
>         par.net       = net;
>         par.table     = table;
> -       par.entryinfo = NULL;
> +       par.entryinfo = &e;

This looks like a completely API burden?

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Xin Long]

On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> (Cc'ing netfilter and Jamal)
>
> On Sat, Aug 5, 2017 at 4:35 AM, Xin Long <lucien.xin@gmail.com> wrote:
>> As we know in some target's checkentry it may dereference par.entryinfo
>> to check entry stuff inside. But when sched action calls xt_check_target,
>> par.entryinfo is set with NULL. It would cause kernel panic when calling
>> some targets.
>>
>> It can be reproduce with:
>>   # tc qd add dev eth1 ingress handle ffff:
>>   # tc filter add dev eth1 parent ffff: u32 match u32 0 0 action xt \
>>     -j ECN --ecn-tcp-remove
>>
>> It could also crash kernel when using target CLUSTERIP or TPROXY.
>>
[1]
>> By now there's no proper value for par.entryinfo in ipt_init_target,
>> but it can not be set with NULL. This patch is to void all these
>> panics by setting it with an ipt_entry obj with all members 0.
>>
>> Signed-off-by: Xin Long <lucien.xin@gmail.com>
>> ---
>>  net/sched/act_ipt.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sched/act_ipt.c b/net/sched/act_ipt.c
>> index 7c4816b..0f09f70 100644
>> --- a/net/sched/act_ipt.c
>> +++ b/net/sched/act_ipt.c
>> @@ -41,6 +41,7 @@ static int ipt_init_target(struct net *net, struct xt_entry_target *t,
>>  {
>>         struct xt_tgchk_param par;
>>         struct xt_target *target;
>> +       struct ipt_entry e;
>>         int ret = 0;
>>
>>         target = xt_request_find_target(AF_INET, t->u.user.name,
>> @@ -48,10 +49,11 @@ static int ipt_init_target(struct net *net, struct xt_entry_target *t,
>>         if (IS_ERR(target))
>>                 return PTR_ERR(target);
>>
>> +       memset(&e, 0, sizeof(e));
>>         t->u.kernel.target = target;
>>         par.net       = net;
>>         par.table     = table;
>> -       par.entryinfo = NULL;
>> +       par.entryinfo = &e;
>
> This looks like a completely API burden?
netfilter xt targets are not really compatible with netsched action.
I've got to say, the patch is just a way to make checkentry return
false and avoid panic. like [1] said

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Cong Wang]

On Mon, Aug 7, 2017 at 7:33 PM, Xin Long <lucien.xin@gmail.com> wrote:
> On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>> This looks like a completely API burden?
> netfilter xt targets are not really compatible with netsched action.
> I've got to say, the patch is just a way to make checkentry return
> false and avoid panic. like [1] said

I don't doubt you fix a crash, I am thinking if we can
"fix" the API instead of fixing the caller.

I am not familiar with this API, so just my 2 cents...

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Xin Long]

On Wed, Aug 9, 2017 at 7:33 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> On Mon, Aug 7, 2017 at 7:33 PM, Xin Long <lucien.xin@gmail.com> wrote:
>> On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>>> This looks like a completely API burden?
>> netfilter xt targets are not really compatible with netsched action.
>> I've got to say, the patch is just a way to make checkentry return
>> false and avoid panic. like [1] said
>
> I don't doubt you fix a crash, I am thinking if we can
> "fix" the API instead of fixing the caller.
Hi, Cong,

For now, I don't think it's possible to change APIs or  some of their targets
for the panic caused by action xt calling.

The common way should be fixed in net_sched side.

Given that the issue is very easy to triggered,
let's wait for netfilter's replies for another few days,
otherwise I will repost the fix, agree ?

>
> I am not familiar with this API, so just my 2 cents...

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Cong Wang]

On Wed, Aug 16, 2017 at 1:39 AM, Xin Long <lucien.xin@gmail.com> wrote:
> On Wed, Aug 9, 2017 at 7:33 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>> On Mon, Aug 7, 2017 at 7:33 PM, Xin Long <lucien.xin@gmail.com> wrote:
>>> On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>>>> This looks like a completely API burden?
>>> netfilter xt targets are not really compatible with netsched action.
>>> I've got to say, the patch is just a way to make checkentry return
>>> false and avoid panic. like [1] said
>>
>> I don't doubt you fix a crash, I am thinking if we can
>> "fix" the API instead of fixing the caller.
> Hi, Cong,
>
> For now, I don't think it's possible to change APIs or  some of their targets
> for the panic caused by action xt calling.
>
> The common way should be fixed in net_sched side.
>
> Given that the issue is very easy to triggered,
> let's wait for netfilter's replies for another few days,
> otherwise I will repost the fix, agree ?

Yeah, no objections from me.

By the way, do you know how other callers of this API
use 'entryinfo'? Do they pass the address of the struct
on stack too?

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Xin Long]

On Thu, Aug 17, 2017 at 5:57 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> On Wed, Aug 16, 2017 at 1:39 AM, Xin Long <lucien.xin@gmail.com> wrote:
>> On Wed, Aug 9, 2017 at 7:33 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>>> On Mon, Aug 7, 2017 at 7:33 PM, Xin Long <lucien.xin@gmail.com> wrote:
>>>> On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>>>>> This looks like a completely API burden?
>>>> netfilter xt targets are not really compatible with netsched action.
>>>> I've got to say, the patch is just a way to make checkentry return
>>>> false and avoid panic. like [1] said
>>>
>>> I don't doubt you fix a crash, I am thinking if we can
>>> "fix" the API instead of fixing the caller.
>> Hi, Cong,
>>
>> For now, I don't think it's possible to change APIs or  some of their targets
>> for the panic caused by action xt calling.
>>
>> The common way should be fixed in net_sched side.
>>
>> Given that the issue is very easy to triggered,
>> let's wait for netfilter's replies for another few days,
>> otherwise I will repost the fix, agree ?
>
> Yeah, no objections from me.
>
> By the way, do you know how other callers of this API
> use 'entryinfo'? Do they pass the address of the struct
> on stack too?
afaik, two places:
1. translate_table -> find_check_entry -> check_target -> xt_check_target
most iptables operations go there and .entryinfo is set in check_target
with struct ipt_entry *e, which is an iptable rule, so can't be NULL.
(as well as ip6table in netfilter/ip6_tables.c )

2. nft_target_init -> xt_check_target, where nft_target_set_tgchk_param
does the exact thing to set .entryinfo with a local varible union nft_entry e:
union nft_entry {
        struct ipt_entry e4;
        struct ip6t_entry e6;
        struct ebt_entry ebt;
        struct arpt_entry arp;
};

case 2 is actually what nft does to use xt targets, so net/sched
action should do
the same.

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Pablo Neira Ayuso]

On Wed, Aug 16, 2017 at 08:39:44PM +1200, Xin Long wrote:
> On Wed, Aug 9, 2017 at 7:33 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> > On Mon, Aug 7, 2017 at 7:33 PM, Xin Long <lucien.xin@gmail.com> wrote:
> >> On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> >>> This looks like a completely API burden?
> >> netfilter xt targets are not really compatible with netsched action.
> >> I've got to say, the patch is just a way to make checkentry return
> >> false and avoid panic. like [1] said
> >
> > I don't doubt you fix a crash, I am thinking if we can
> > "fix" the API instead of fixing the caller.
> Hi, Cong,
> 
> For now, I don't think it's possible to change APIs or  some of their targets
> for the panic caused by action xt calling.
> 
> The common way should be fixed in net_sched side.
> 
> Given that the issue is very easy to triggered,
> let's wait for netfilter's replies for another few days,
> otherwise I will repost the fix, agree ?

Please, post the workaround so the kernel doesn't crash anymore.

This is going to be very hard to fix, it's broken since the very
beginning...

Thanks!

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Pablo Neira Ayuso]

On Thu, Aug 17, 2017 at 12:02:20PM +0200, Pablo Neira Ayuso wrote:
> On Wed, Aug 16, 2017 at 08:39:44PM +1200, Xin Long wrote:
> > On Wed, Aug 9, 2017 at 7:33 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> > > On Mon, Aug 7, 2017 at 7:33 PM, Xin Long <lucien.xin@gmail.com> wrote:
> > >> On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> > >>> This looks like a completely API burden?
> > >> netfilter xt targets are not really compatible with netsched action.
> > >> I've got to say, the patch is just a way to make checkentry return
> > >> false and avoid panic. like [1] said
> > >
> > > I don't doubt you fix a crash, I am thinking if we can
> > > "fix" the API instead of fixing the caller.
> > Hi, Cong,
> > 
> > For now, I don't think it's possible to change APIs or  some of their targets
> > for the panic caused by action xt calling.
> > 
> > The common way should be fixed in net_sched side.
> > 
> > Given that the issue is very easy to triggered,
> > let's wait for netfilter's replies for another few days,
> > otherwise I will repost the fix, agree ?
> 
> Please, post the workaround so the kernel doesn't crash anymore.
> 
> This is going to be very hard to fix, it's broken since the very
> beginning...

Wait a second, you could rename par->nft_compat to par->no_entry. From
net/sched/ you can set this to 1, so the entry checks are ignored.

I'm refering to patch 55917a21d0cc0

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Xin Long]

On Thu, Aug 17, 2017 at 10:33 PM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Thu, Aug 17, 2017 at 12:02:20PM +0200, Pablo Neira Ayuso wrote:
>> On Wed, Aug 16, 2017 at 08:39:44PM +1200, Xin Long wrote:
>> > On Wed, Aug 9, 2017 at 7:33 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>> > > On Mon, Aug 7, 2017 at 7:33 PM, Xin Long <lucien.xin@gmail.com> wrote:
>> > >> On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>> > >>> This looks like a completely API burden?
>> > >> netfilter xt targets are not really compatible with netsched action.
>> > >> I've got to say, the patch is just a way to make checkentry return
>> > >> false and avoid panic. like [1] said
>> > >
>> > > I don't doubt you fix a crash, I am thinking if we can
>> > > "fix" the API instead of fixing the caller.
>> > Hi, Cong,
>> >
>> > For now, I don't think it's possible to change APIs or  some of their targets
>> > for the panic caused by action xt calling.
>> >
>> > The common way should be fixed in net_sched side.
>> >
>> > Given that the issue is very easy to triggered,
>> > let's wait for netfilter's replies for another few days,
>> > otherwise I will repost the fix, agree ?
>>
>> Please, post the workaround so the kernel doesn't crash anymore.
>>
>> This is going to be very hard to fix, it's broken since the very
>> beginning...
>
> Wait a second, you could rename par->nft_compat to par->no_entry. From
> net/sched/ you can set this to 1, so the entry checks are ignored.
>
> I'm refering to patch 55917a21d0cc0

par->nft_compat wasn't used to ignore the entry checks, if we rename it
as no_entry, some other targets still needs to update. like the ones in
this patch's changelog:
ECN: ecn_tg_check()
TPROXY: tproxy_tg4_check()

which means these two checks will be ignored for nft as well, that is
not what we want.
As nft has e4.ip.proto and e4.ip.invflags being set which net/sched
gets nothing. they are still different.

Re: [PATCH net] net: sched: fix NULL pointer dereference when action calls some targets

[Pablo Neira Ayuso]

On Thu, Aug 17, 2017 at 11:24:00PM +1200, Xin Long wrote:
> On Thu, Aug 17, 2017 at 10:33 PM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > On Thu, Aug 17, 2017 at 12:02:20PM +0200, Pablo Neira Ayuso wrote:
> >> On Wed, Aug 16, 2017 at 08:39:44PM +1200, Xin Long wrote:
> >> > On Wed, Aug 9, 2017 at 7:33 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> >> > > On Mon, Aug 7, 2017 at 7:33 PM, Xin Long <lucien.xin@gmail.com> wrote:
> >> > >> On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> >> > >>> This looks like a completely API burden?
> >> > >> netfilter xt targets are not really compatible with netsched action.
> >> > >> I've got to say, the patch is just a way to make checkentry return
> >> > >> false and avoid panic. like [1] said
> >> > >
> >> > > I don't doubt you fix a crash, I am thinking if we can
> >> > > "fix" the API instead of fixing the caller.
> >> > Hi, Cong,
> >> >
> >> > For now, I don't think it's possible to change APIs or  some of their targets
> >> > for the panic caused by action xt calling.
> >> >
> >> > The common way should be fixed in net_sched side.
> >> >
> >> > Given that the issue is very easy to triggered,
> >> > let's wait for netfilter's replies for another few days,
> >> > otherwise I will repost the fix, agree ?
> >>
> >> Please, post the workaround so the kernel doesn't crash anymore.
> >>
> >> This is going to be very hard to fix, it's broken since the very
> >> beginning...
> >
> > Wait a second, you could rename par->nft_compat to par->no_entry. From
> > net/sched/ you can set this to 1, so the entry checks are ignored.
> >
> > I'm refering to patch 55917a21d0cc0
> 
> par->nft_compat wasn't used to ignore the entry checks, if we rename it
> as no_entry, some other targets still needs to update. like the ones in
> this patch's changelog:
> ECN: ecn_tg_check()
> TPROXY: tproxy_tg4_check()
> 
> which means these two checks will be ignored for nft as well, that is
> not what we want.
> As nft has e4.ip.proto and e4.ip.invflags being set which net/sched
> gets nothing. they are still different.

I see, then just fix this crash. It's been known among people that the
number of extensions that act_ipt supports is limited.

Thanks.