Re: [Patch net] net_sched: add max len check for TCA_KIND

On Fri, 4 Oct 2019 16:23:40 -0700, Cong Wang wrote:

On Fri, Oct 4, 2019 at 3:54 PM Jakub Kicinski wrote:

quoted

On Thu, 3 Oct 2019 16:45:25 -0300, Marcelo Ricardo Leitner wrote:  

quoted

On Sat, Sep 21, 2019 at 07:24:34PM -0700, Jakub Kicinski wrote:  

quoted

Applied, queued for 4.14+, thanks!  

Ahm, this breaks some user applications.

I'm getting "Attribute failed policy validation" extack error while
adding ingress qdisc on an app using libmnl, because it just doesn't
pack the null byte there if it uses mnl_attr_put_str():
https://git.netfilter.org/libmnl/tree/src/attr.c#n481
Unless it uses mnl_attr_put_strz() instead.

Though not sure who's to blame here, as one could argue that the
app should have been using the latter in the first place, but well..
it worked and produced the right results.

Ditto for 199ce850ce11 ("net_sched: add policy validation for action
attributes") on TCA_ACT_KIND.  

Thanks for the report Marcelo! This netlink validation stuff is always
super risky I figured better find out if something breaks sooner than
later, hence the backport.

So if I'm understanding this would be the fix?  

Of course not, you just break KMSAN again. Please read the original
report.

The fix for the regression. I'm establishing the rest of 199ce850ce11
("net_sched: add policy validation for action attributes") is fine.

I mentioned this brings back the problem KMSAN reported in the part of
the email you cut off. str*cpy is the obvious answer for reimplementing
that fix.

I will send a patch

Please do.