On Fri, Sep 15, 2023 at 12:42 PM Ma Ke <[email protected]> wrote:
>
> If asked to drop a packet via TC_ACT_SHOT it is unsafe to
> assume res.class contains a valid pointer.
>
> Signed-off-by: Ma Ke <[email protected]>
> ---
> net/sched/sch_drr.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
> index 19901e77cd3b..2b854cb6edf9 100644
> --- a/net/sched/sch_drr.c
> +++ b/net/sched/sch_drr.c
> @@ -309,6 +309,8 @@ static struct drr_class *drr_classify(struct sk_buff *skb, struct Qdisc *sch,
> *qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
> fl = rcu_dereference_bh(q->filter_list);
> result = tcf_classify(skb, NULL, fl, &res, false);
> + if (result == TC_ACT_SHOT)
> + return NULL;
> if (result >= 0) {
> #ifdef CONFIG_NET_CLS_ACT
> switch (result) {
> --
> 2.37.2
>
I do not see a bug, TC_ACT_SHOT is handled in the switch (result) just fine
at line 320 ?
On 15/09/2023 09:55, Eric Dumazet wrote:
> On Fri, Sep 15, 2023 at 12:42 PM Ma Ke <[email protected]> wrote:
>>
>> If asked to drop a packet via TC_ACT_SHOT it is unsafe to
>> assume res.class contains a valid pointer.
>>
>> Signed-off-by: Ma Ke <[email protected]>
>> ---
>> net/sched/sch_drr.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
>> index 19901e77cd3b..2b854cb6edf9 100644
>> --- a/net/sched/sch_drr.c
>> +++ b/net/sched/sch_drr.c
>> @@ -309,6 +309,8 @@ static struct drr_class *drr_classify(struct sk_buff *skb, struct Qdisc *sch,
>> *qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
>> fl = rcu_dereference_bh(q->filter_list);
>> result = tcf_classify(skb, NULL, fl, &res, false);
>> + if (result == TC_ACT_SHOT)
>> + return NULL;
>> if (result >= 0) {
>> #ifdef CONFIG_NET_CLS_ACT
>> switch (result) {
>> --
>> 2.37.2
>>
>
> I do not see a bug, TC_ACT_SHOT is handled in the switch (result) just fine
> at line 320 ?
Following the code path (with CONFIG_NET_CLS_ACT=n in mind), it looks
like there are a couple of places which return TC_ACT_SHOT before
calling any classifiers, which then would cause some qdiscs to look into
a uninitialized 'struct tcf_result res'.
I could be misreading it... But if it's the problem the author is trying
to fix, the obvious way to do it would be:
struct tcf_result res = {};
On Fri, Sep 15, 2023 at 5:03 PM Pedro Tammela <[email protected]> wrote:
>
> On 15/09/2023 09:55, Eric Dumazet wrote:
> > On Fri, Sep 15, 2023 at 12:42 PM Ma Ke <[email protected]> wrote:
> >>
> >> If asked to drop a packet via TC_ACT_SHOT it is unsafe to
> >> assume res.class contains a valid pointer.
> >>
> >> Signed-off-by: Ma Ke <[email protected]>
> >> ---
> >> net/sched/sch_drr.c | 2 ++
> >> 1 file changed, 2 insertions(+)
> >>
> >> diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
> >> index 19901e77cd3b..2b854cb6edf9 100644
> >> --- a/net/sched/sch_drr.c
> >> +++ b/net/sched/sch_drr.c
> >> @@ -309,6 +309,8 @@ static struct drr_class *drr_classify(struct sk_buff *skb, struct Qdisc *sch,
> >> *qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
> >> fl = rcu_dereference_bh(q->filter_list);
> >> result = tcf_classify(skb, NULL, fl, &res, false);
> >> + if (result == TC_ACT_SHOT)
> >> + return NULL;
> >> if (result >= 0) {
> >> #ifdef CONFIG_NET_CLS_ACT
> >> switch (result) {
> >> --
> >> 2.37.2
> >>
> >
> > I do not see a bug, TC_ACT_SHOT is handled in the switch (result) just fine
> > at line 320 ?
>
> Following the code path (with CONFIG_NET_CLS_ACT=n in mind), it looks
> like there are a couple of places which return TC_ACT_SHOT before
> calling any classifiers, which then would cause some qdiscs to look into
> a uninitialized 'struct tcf_result res'.
> I could be misreading it... But if it's the problem the author is trying
> to fix, the obvious way to do it would be:
> struct tcf_result res = {};
CONFIG_NET_CLS_ACT=n, how come TC_ACT_SHOT could be used ?
Can we get rid of CONFIG_NET_CLS_ACT, this seems obfuscation to me at
this point.
On Fri, Sep 15, 2023 at 11:06 AM Eric Dumazet <[email protected]> wrote:
>
> On Fri, Sep 15, 2023 at 5:03 PM Pedro Tammela <[email protected]> wrote:
> >
> > On 15/09/2023 09:55, Eric Dumazet wrote:
> > > On Fri, Sep 15, 2023 at 12:42 PM Ma Ke <[email protected]> wrote:
> > >>
> > >> If asked to drop a packet via TC_ACT_SHOT it is unsafe to
> > >> assume res.class contains a valid pointer.
> > >>
> > >> Signed-off-by: Ma Ke <[email protected]>
> > >> ---
> > >> net/sched/sch_drr.c | 2 ++
> > >> 1 file changed, 2 insertions(+)
> > >>
> > >> diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
> > >> index 19901e77cd3b..2b854cb6edf9 100644
> > >> --- a/net/sched/sch_drr.c
> > >> +++ b/net/sched/sch_drr.c
> > >> @@ -309,6 +309,8 @@ static struct drr_class *drr_classify(struct sk_buff *skb, struct Qdisc *sch,
> > >> *qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
> > >> fl = rcu_dereference_bh(q->filter_list);
> > >> result = tcf_classify(skb, NULL, fl, &res, false);
> > >> + if (result == TC_ACT_SHOT)
> > >> + return NULL;
> > >> if (result >= 0) {
> > >> #ifdef CONFIG_NET_CLS_ACT
> > >> switch (result) {
> > >> --
> > >> 2.37.2
> > >>
> > >
> > > I do not see a bug, TC_ACT_SHOT is handled in the switch (result) just fine
> > > at line 320 ?
> >
> > Following the code path (with CONFIG_NET_CLS_ACT=n in mind), it looks
> > like there are a couple of places which return TC_ACT_SHOT before
> > calling any classifiers, which then would cause some qdiscs to look into
> > a uninitialized 'struct tcf_result res'.
> > I could be misreading it... But if it's the problem the author is trying
> > to fix, the obvious way to do it would be:
> > struct tcf_result res = {};
>
> CONFIG_NET_CLS_ACT=n, how come TC_ACT_SHOT could be used ?
>
> Can we get rid of CONFIG_NET_CLS_ACT, this seems obfuscation to me at
> this point.
The problem is the verdict vs return code are intermixed - not saying
this was fixing anything useful.
We discussed this in the past after/during commit
caa4b35b4317d5147b3ab0fbdc9c075c7d2e9c12
Victor worked on a patch to resolve that. Victor, maybe revive that
patch and post as RFC?
cheers,
jamal