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

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 [off-list ref] wrote:

quoted

On Thu, Aug 17, 2017 at 12:02:20PM +0200, Pablo Neira Ayuso wrote:

quoted

On Wed, Aug 16, 2017 at 08:39:44PM +1200, Xin Long wrote:

quoted

On Wed, Aug 9, 2017 at 7:33 AM, Cong Wang [off-list ref] wrote:

quoted

On Mon, Aug 7, 2017 at 7:33 PM, Xin Long [off-list ref] wrote:

quoted

On Tue, Aug 8, 2017 at 9:15 AM, Cong Wang [off-list ref] wrote:

quoted

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.