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

[Jakub Kicinski <jakub.kicinski@netronome.com>]

On Thu, 3 Oct 2019 16:45:25 -0300, Marcelo Ricardo Leitner wrote:
> On Sat, Sep 21, 2019 at 07:24:34PM -0700, Jakub Kicinski wrote:
> > 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?

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index 2558f00f6b3e..bcc1178ce50d 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -832,8 +832,7 @@ static struct tc_cookie *nla_memdup_cookie(struct nlattr **tb)
 }
 
 static const struct nla_policy tcf_action_policy[TCA_ACT_MAX + 1] = {
-       [TCA_ACT_KIND]          = { .type = NLA_NUL_STRING,
-                                   .len = IFNAMSIZ - 1 },
+       [TCA_ACT_KIND]          = { .type = NLA_STRING },
        [TCA_ACT_INDEX]         = { .type = NLA_U32 },
        [TCA_ACT_COOKIE]        = { .type = NLA_BINARY,
                                    .len = TC_COOKIE_MAX_SIZE },
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 81d58b280612..1047825d9f48 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1390,8 +1390,7 @@ check_loop_fn(struct Qdisc *q, unsigned long cl, struct qdisc_walker *w)
 }
 
 const struct nla_policy rtm_tca_policy[TCA_MAX + 1] = {
-       [TCA_KIND]              = { .type = NLA_NUL_STRING,
-                                   .len = IFNAMSIZ - 1 },
+       [TCA_KIND]              = { .type = NLA_STRING },
        [TCA_RATE]              = { .type = NLA_BINARY,
                                    .len = sizeof(struct tc_estimator) },
        [TCA_STAB]              = { .type = NLA_NESTED },


Cong, are you planning to take a look? With this we have to find a
different way to deal with the KMSAN report you mentioned :(