net/bridge/br_input.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
Since commit 751de2012eaf ("netfilter: br_netfilter: skip conntrack input hook for promisc packets")
a second argument (promisc) has been added to br_pass_frame_up which
represents whether the interface is in promiscuous mode. However,
internally - in one remaining case - br_pass_frame_up checks the device
flags derived from skb instead of the argument being passed in.
This one-line changes addresses this inconsistency.
Signed-off-by: Amedeo Baragiola <ingamedeo@gmail.com>
---
net/bridge/br_input.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index ceaa5a89b947..156c18f42fa3 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -50,8 +50,7 @@ static int br_pass_frame_up(struct sk_buff *skb, bool promisc)
* packet is allowed except in promisc mode when someone
* may be running packet capture.
*/
- if (!(brdev->flags & IFF_PROMISC) &&
- !br_allowed_egress(vg, skb)) {
+ if (!promisc && !br_allowed_egress(vg, skb)) {
kfree_skb(skb);
return NET_RX_DROP;
}
--
2.46.2On 05/10/2024 04:44, Amedeo Baragiola wrote:
> Since commit 751de2012eaf ("netfilter: br_netfilter: skip conntrack input hook for promisc packets")
> a second argument (promisc) has been added to br_pass_frame_up which
> represents whether the interface is in promiscuous mode. However,
> internally - in one remaining case - br_pass_frame_up checks the device
> flags derived from skb instead of the argument being passed in.
> This one-line changes addresses this inconsistency.
>
> Signed-off-by: Amedeo Baragiola <ingamedeo@gmail.com>
> ---
> net/bridge/br_input.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> index ceaa5a89b947..156c18f42fa3 100644
> --- a/net/bridge/br_input.c
> +++ b/net/bridge/br_input.c
> @@ -50,8 +50,7 @@ static int br_pass_frame_up(struct sk_buff *skb, bool promisc)
> * packet is allowed except in promisc mode when someone
> * may be running packet capture.
> */
> - if (!(brdev->flags & IFF_PROMISC) &&
> - !br_allowed_egress(vg, skb)) {
> + if (!promisc && !br_allowed_egress(vg, skb)) {
> kfree_skb(skb);
> return NET_RX_DROP;
> }
This is subtle, but it does change behaviour when a BR_FDB_LOCAL dst
is found it will always drop the traffic after this patch (w/ promisc) if it
doesn't pass br_allowed_egress(). It would've been allowed before, but current
situation does make the patch promisc bit inconsistent, i.e. we get
there because of BR_FDB_LOCAL regardless of the promisc flag.
Because we can have a BR_FDB_LOCAL dst and still pass up such skb because of
the flag instead of local_rcv (see br_br_handle_frame_finish()).
CCing also Pablo for a second pair of eyes and as the original patch
author. :)
Pablo WDYT?
Just FYI we definitely want to see all traffic if promisc is set, so
this patch is a no-go.
Cheers,
Nik
Hi Nikolay,
On Sat, Oct 05, 2024 at 05:06:56PM +0300, Nikolay Aleksandrov wrote:
> On 05/10/2024 04:44, Amedeo Baragiola wrote:
> > Since commit 751de2012eaf ("netfilter: br_netfilter: skip conntrack input hook for promisc packets")
> > a second argument (promisc) has been added to br_pass_frame_up which
> > represents whether the interface is in promiscuous mode. However,
> > internally - in one remaining case - br_pass_frame_up checks the device
> > flags derived from skb instead of the argument being passed in.
> > This one-line changes addresses this inconsistency.
> >
> > Signed-off-by: Amedeo Baragiola <ingamedeo@gmail.com>
> > ---
> > net/bridge/br_input.c | 3 +--
> > 1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> > index ceaa5a89b947..156c18f42fa3 100644
> > --- a/net/bridge/br_input.c
> > +++ b/net/bridge/br_input.c
> > @@ -50,8 +50,7 @@ static int br_pass_frame_up(struct sk_buff *skb, bool promisc)
> > * packet is allowed except in promisc mode when someone
> > * may be running packet capture.
> > */
> > - if (!(brdev->flags & IFF_PROMISC) &&
> > - !br_allowed_egress(vg, skb)) {
> > + if (!promisc && !br_allowed_egress(vg, skb)) {
> > kfree_skb(skb);
> > return NET_RX_DROP;
> > }
>
> This is subtle, but it does change behaviour when a BR_FDB_LOCAL dst
> is found it will always drop the traffic after this patch (w/ promisc) if it
> doesn't pass br_allowed_egress(). It would've been allowed before, but current
> situation does make the patch promisc bit inconsistent, i.e. we get
> there because of BR_FDB_LOCAL regardless of the promisc flag.
>
> Because we can have a BR_FDB_LOCAL dst and still pass up such skb because of
> the flag instead of local_rcv (see br_br_handle_frame_finish()).
>
> CCing also Pablo for a second pair of eyes and as the original patch
> author. :)
>
> Pablo WDYT?
>
> Just FYI we definitely want to see all traffic if promisc is set, so
> this patch is a no-go.
promisc is always _false_ for BR_FDB_LOCAL dst:
if (dst) {
unsigned long now = jiffies;
if (test_bit(BR_FDB_LOCAL, &dst->flags))
return br_pass_frame_up(skb, false);
...
}
if (local_rcv)
return br_pass_frame_up(skb, promisc);
> > - if (!(brdev->flags & IFF_PROMISC) &&
> > - !br_allowed_egress(vg, skb)) {
> > + if (!promisc && !br_allowed_egress(vg, skb)) {
Then, this is not equivalent.
But, why is br_allowed_egress() skipped depending on brdev->flags & IFF_PROMISC?
I mean, how does this combination work?
BR_FDB_LOCAL dst AND (brdev->flags & IFF_PROMISC) AND BR_INPUT_SKB_CB(skb)->vlan_filtered
> > kfree_skb(skb);
> > return NET_RX_DROP;
> > }
On 08/10/2024 17:30, Pablo Neira Ayuso wrote:
> Hi Nikolay,
>
> On Sat, Oct 05, 2024 at 05:06:56PM +0300, Nikolay Aleksandrov wrote:
>> On 05/10/2024 04:44, Amedeo Baragiola wrote:
>>> Since commit 751de2012eaf ("netfilter: br_netfilter: skip conntrack input hook for promisc packets")
>>> a second argument (promisc) has been added to br_pass_frame_up which
>>> represents whether the interface is in promiscuous mode. However,
>>> internally - in one remaining case - br_pass_frame_up checks the device
>>> flags derived from skb instead of the argument being passed in.
>>> This one-line changes addresses this inconsistency.
>>>
>>> Signed-off-by: Amedeo Baragiola <ingamedeo@gmail.com>
>>> ---
>>> net/bridge/br_input.c | 3 +--
>>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
>>> index ceaa5a89b947..156c18f42fa3 100644
>>> --- a/net/bridge/br_input.c
>>> +++ b/net/bridge/br_input.c
>>> @@ -50,8 +50,7 @@ static int br_pass_frame_up(struct sk_buff *skb, bool promisc)
>>> * packet is allowed except in promisc mode when someone
>>> * may be running packet capture.
>>> */
>>> - if (!(brdev->flags & IFF_PROMISC) &&
>>> - !br_allowed_egress(vg, skb)) {
>>> + if (!promisc && !br_allowed_egress(vg, skb)) {
>>> kfree_skb(skb);
>>> return NET_RX_DROP;
>>> }
>>
>> This is subtle, but it does change behaviour when a BR_FDB_LOCAL dst
>> is found it will always drop the traffic after this patch (w/ promisc) if it
>> doesn't pass br_allowed_egress(). It would've been allowed before, but current
>> situation does make the patch promisc bit inconsistent, i.e. we get
>> there because of BR_FDB_LOCAL regardless of the promisc flag.
>>
>> Because we can have a BR_FDB_LOCAL dst and still pass up such skb because of
>> the flag instead of local_rcv (see br_br_handle_frame_finish()).
>>
>> CCing also Pablo for a second pair of eyes and as the original patch
>> author. :)
>>
>> Pablo WDYT?
>>
>> Just FYI we definitely want to see all traffic if promisc is set, so
>> this patch is a no-go.
>
> promisc is always _false_ for BR_FDB_LOCAL dst:
>
> if (dst) {
> unsigned long now = jiffies;
>
> if (test_bit(BR_FDB_LOCAL, &dst->flags))
> return br_pass_frame_up(skb, false);
>
> ...
> }
>
> if (local_rcv)
> return br_pass_frame_up(skb, promisc);
>
>>> - if (!(brdev->flags & IFF_PROMISC) &&
>>> - !br_allowed_egress(vg, skb)) {
>>> + if (!promisc && !br_allowed_egress(vg, skb)) {
>
> Then, this is not equivalent.
>
> But, why is br_allowed_egress() skipped depending on brdev->flags & IFF_PROMISC?
>
> I mean, how does this combination work?
>
> BR_FDB_LOCAL dst AND (brdev->flags & IFF_PROMISC) AND BR_INPUT_SKB_CB(skb)->vlan_filtered
The bridge should see all packets come up if promisc flag is set, regardless if the
vlan exists or not, so br_allowed_egress() is skipped entirely. As I commented
separately the patch changes that behaviour and suddenly these packets
(BR_FDB_LOCAL fdb + promisc bit set on the bridge dev) won't be sent up to
the bridge. I think the current code should stay as-is, but wanted to get
your opinion if we can still hit the warning that was fixed because we can
still hit that code with a BR_FDB_LOCAL dst with promisc flag set and
the promisc flag will be == false in that case.
On Tue, Oct 08, 2024 at 05:45:44PM +0300, Nikolay Aleksandrov wrote:
> On 08/10/2024 17:30, Pablo Neira Ayuso wrote:
> > Hi Nikolay,
> >
> > On Sat, Oct 05, 2024 at 05:06:56PM +0300, Nikolay Aleksandrov wrote:
> >> On 05/10/2024 04:44, Amedeo Baragiola wrote:
> >>> Since commit 751de2012eaf ("netfilter: br_netfilter: skip conntrack input hook for promisc packets")
> >>> a second argument (promisc) has been added to br_pass_frame_up which
> >>> represents whether the interface is in promiscuous mode. However,
> >>> internally - in one remaining case - br_pass_frame_up checks the device
> >>> flags derived from skb instead of the argument being passed in.
> >>> This one-line changes addresses this inconsistency.
> >>>
> >>> Signed-off-by: Amedeo Baragiola <ingamedeo@gmail.com>
> >>> ---
> >>> net/bridge/br_input.c | 3 +--
> >>> 1 file changed, 1 insertion(+), 2 deletions(-)
> >>>
> >>> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> >>> index ceaa5a89b947..156c18f42fa3 100644
> >>> --- a/net/bridge/br_input.c
> >>> +++ b/net/bridge/br_input.c
> >>> @@ -50,8 +50,7 @@ static int br_pass_frame_up(struct sk_buff *skb, bool promisc)
> >>> * packet is allowed except in promisc mode when someone
> >>> * may be running packet capture.
> >>> */
> >>> - if (!(brdev->flags & IFF_PROMISC) &&
> >>> - !br_allowed_egress(vg, skb)) {
> >>> + if (!promisc && !br_allowed_egress(vg, skb)) {
> >>> kfree_skb(skb);
> >>> return NET_RX_DROP;
> >>> }
> >>
> >> This is subtle, but it does change behaviour when a BR_FDB_LOCAL dst
> >> is found it will always drop the traffic after this patch (w/ promisc) if it
> >> doesn't pass br_allowed_egress(). It would've been allowed before, but current
> >> situation does make the patch promisc bit inconsistent, i.e. we get
> >> there because of BR_FDB_LOCAL regardless of the promisc flag.
> >>
> >> Because we can have a BR_FDB_LOCAL dst and still pass up such skb because of
> >> the flag instead of local_rcv (see br_br_handle_frame_finish()).
> >>
> >> CCing also Pablo for a second pair of eyes and as the original patch
> >> author. :)
> >>
> >> Pablo WDYT?
> >>
> >> Just FYI we definitely want to see all traffic if promisc is set, so
> >> this patch is a no-go.
> >
> > promisc is always _false_ for BR_FDB_LOCAL dst:
> >
> > if (dst) {
> > unsigned long now = jiffies;
> >
> > if (test_bit(BR_FDB_LOCAL, &dst->flags))
> > return br_pass_frame_up(skb, false);
> >
> > ...
> > }
> >
> > if (local_rcv)
> > return br_pass_frame_up(skb, promisc);
> >
> >>> - if (!(brdev->flags & IFF_PROMISC) &&
> >>> - !br_allowed_egress(vg, skb)) {
> >>> + if (!promisc && !br_allowed_egress(vg, skb)) {
> >
> > Then, this is not equivalent.
> >
> > But, why is br_allowed_egress() skipped depending on brdev->flags & IFF_PROMISC?
> >
> > I mean, how does this combination work?
> >
> > BR_FDB_LOCAL dst AND (brdev->flags & IFF_PROMISC) AND BR_INPUT_SKB_CB(skb)->vlan_filtered
>
> The bridge should see all packets come up if promisc flag is set, regardless if the
> vlan exists or not, so br_allowed_egress() is skipped entirely.
I see, but does this defeat the purpose of the vlan bridge filtering
for BR_FDB_LOCAL dst while IFF_PROMISC is on?
> As I commented separately the patch changes that behaviour and
> suddenly these packets (BR_FDB_LOCAL fdb + promisc bit set on the
> bridge dev) won't be sent up to the bridge.
I agree this proposed patch does not improve the situation.
> I think the current code should stay as-is, but wanted to get your
> opinion if we can still hit the warning that was fixed because we
> can still hit that code with a BR_FDB_LOCAL dst with promisc flag
> set and the promisc flag will be == false in that case.
Packets with BR_FDB_LOCAL dst are unicast packets but
skb->pkt_type != PACKET_HOST?
On 08/10/2024 18:44, Pablo Neira Ayuso wrote:
> On Tue, Oct 08, 2024 at 05:45:44PM +0300, Nikolay Aleksandrov wrote:
>> On 08/10/2024 17:30, Pablo Neira Ayuso wrote:
>>> Hi Nikolay,
>>>
>>> On Sat, Oct 05, 2024 at 05:06:56PM +0300, Nikolay Aleksandrov wrote:
>>>> On 05/10/2024 04:44, Amedeo Baragiola wrote:
>>>>> Since commit 751de2012eaf ("netfilter: br_netfilter: skip conntrack input hook for promisc packets")
>>>>> a second argument (promisc) has been added to br_pass_frame_up which
>>>>> represents whether the interface is in promiscuous mode. However,
>>>>> internally - in one remaining case - br_pass_frame_up checks the device
>>>>> flags derived from skb instead of the argument being passed in.
>>>>> This one-line changes addresses this inconsistency.
>>>>>
>>>>> Signed-off-by: Amedeo Baragiola <ingamedeo@gmail.com>
>>>>> ---
>>>>> net/bridge/br_input.c | 3 +--
>>>>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
>>>>> index ceaa5a89b947..156c18f42fa3 100644
>>>>> --- a/net/bridge/br_input.c
>>>>> +++ b/net/bridge/br_input.c
>>>>> @@ -50,8 +50,7 @@ static int br_pass_frame_up(struct sk_buff *skb, bool promisc)
>>>>> * packet is allowed except in promisc mode when someone
>>>>> * may be running packet capture.
>>>>> */
>>>>> - if (!(brdev->flags & IFF_PROMISC) &&
>>>>> - !br_allowed_egress(vg, skb)) {
>>>>> + if (!promisc && !br_allowed_egress(vg, skb)) {
>>>>> kfree_skb(skb);
>>>>> return NET_RX_DROP;
>>>>> }
>>>>
>>>> This is subtle, but it does change behaviour when a BR_FDB_LOCAL dst
>>>> is found it will always drop the traffic after this patch (w/ promisc) if it
>>>> doesn't pass br_allowed_egress(). It would've been allowed before, but current
>>>> situation does make the patch promisc bit inconsistent, i.e. we get
>>>> there because of BR_FDB_LOCAL regardless of the promisc flag.
>>>>
>>>> Because we can have a BR_FDB_LOCAL dst and still pass up such skb because of
>>>> the flag instead of local_rcv (see br_br_handle_frame_finish()).
>>>>
>>>> CCing also Pablo for a second pair of eyes and as the original patch
>>>> author. :)
>>>>
>>>> Pablo WDYT?
>>>>
>>>> Just FYI we definitely want to see all traffic if promisc is set, so
>>>> this patch is a no-go.
>>>
>>> promisc is always _false_ for BR_FDB_LOCAL dst:
>>>
>>> if (dst) {
>>> unsigned long now = jiffies;
>>>
>>> if (test_bit(BR_FDB_LOCAL, &dst->flags))
>>> return br_pass_frame_up(skb, false);
>>>
>>> ...
>>> }
>>>
>>> if (local_rcv)
>>> return br_pass_frame_up(skb, promisc);
>>>
>>>>> - if (!(brdev->flags & IFF_PROMISC) &&
>>>>> - !br_allowed_egress(vg, skb)) {
>>>>> + if (!promisc && !br_allowed_egress(vg, skb)) {
>>>
>>> Then, this is not equivalent.
>>>
>>> But, why is br_allowed_egress() skipped depending on brdev->flags & IFF_PROMISC?
>>>
>>> I mean, how does this combination work?
>>>
>>> BR_FDB_LOCAL dst AND (brdev->flags & IFF_PROMISC) AND BR_INPUT_SKB_CB(skb)->vlan_filtered
>>
>> The bridge should see all packets come up if promisc flag is set, regardless if the
>> vlan exists or not, so br_allowed_egress() is skipped entirely.
>
> I see, but does this defeat the purpose of the vlan bridge filtering
> for BR_FDB_LOCAL dst while IFF_PROMISC is on?
>
Yes, it does, but it is expected behaviour with promisc on.
>> As I commented separately the patch changes that behaviour and
>> suddenly these packets (BR_FDB_LOCAL fdb + promisc bit set on the
>> bridge dev) won't be sent up to the bridge.
>
> I agree this proposed patch does not improve the situation.
>
>> I think the current code should stay as-is, but wanted to get your
>> opinion if we can still hit the warning that was fixed because we
>> can still hit that code with a BR_FDB_LOCAL dst with promisc flag
>> set and the promisc flag will be == false in that case.
>
> Packets with BR_FDB_LOCAL dst are unicast packets but
> skb->pkt_type != PACKET_HOST?
BR_FDB_LOCAL just marks the skb to be passed up the stack (terminated
locally) with the bridge device set in skb->dev, it may or may not be PACKET_HOST.
I agree, just patch actually changes the behaviour when a BR_FDB_LOCAL
dst is found and drops the traffic because promisc is *always* set to
false when a BR_FDB_LOCAL dst is found in br_handle_frame_finish().
I guess the problem I was trying to solve was that since the
introduction of the promisc flag we still use brdev->flags &
IFF_PROMISC in br_pass_frame_up() which is essentially the value of
promisc (except in the BR_FDB_LOCAL case above) instead of promisc
itself.
Amedeo
On Sat, Oct 5, 2024 at 7:06 AM Nikolay Aleksandrov <razor@blackwall.org> wrote:
>
> On 05/10/2024 04:44, Amedeo Baragiola wrote:
> > Since commit 751de2012eaf ("netfilter: br_netfilter: skip conntrack input hook for promisc packets")
> > a second argument (promisc) has been added to br_pass_frame_up which
> > represents whether the interface is in promiscuous mode. However,
> > internally - in one remaining case - br_pass_frame_up checks the device
> > flags derived from skb instead of the argument being passed in.
> > This one-line changes addresses this inconsistency.
> >
> > Signed-off-by: Amedeo Baragiola <ingamedeo@gmail.com>
> > ---
> > net/bridge/br_input.c | 3 +--
> > 1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> > index ceaa5a89b947..156c18f42fa3 100644
> > --- a/net/bridge/br_input.c
> > +++ b/net/bridge/br_input.c
> > @@ -50,8 +50,7 @@ static int br_pass_frame_up(struct sk_buff *skb, bool promisc)
> > * packet is allowed except in promisc mode when someone
> > * may be running packet capture.
> > */
> > - if (!(brdev->flags & IFF_PROMISC) &&
> > - !br_allowed_egress(vg, skb)) {
> > + if (!promisc && !br_allowed_egress(vg, skb)) {
> > kfree_skb(skb);
> > return NET_RX_DROP;
> > }
>
> This is subtle, but it does change behaviour when a BR_FDB_LOCAL dst
> is found it will always drop the traffic after this patch (w/ promisc) if it
> doesn't pass br_allowed_egress(). It would've been allowed before, but current
> situation does make the patch promisc bit inconsistent, i.e. we get
> there because of BR_FDB_LOCAL regardless of the promisc flag.
>
> Because we can have a BR_FDB_LOCAL dst and still pass up such skb because of
> the flag instead of local_rcv (see br_br_handle_frame_finish()).
>
> CCing also Pablo for a second pair of eyes and as the original patch
> author. :)
>
> Pablo WDYT?
>
> Just FYI we definitely want to see all traffic if promisc is set, so
> this patch is a no-go.
>
> Cheers,
> Nik
--
Thanks,
Amedeo
On 06/10/2024 20:24, Amedeo Baragiola wrote: > I agree, just patch actually changes the behaviour when a BR_FDB_LOCAL > dst is found and drops the traffic because promisc is *always* set to > false when a BR_FDB_LOCAL dst is found in br_handle_frame_finish(). > I guess the problem I was trying to solve was that since the > introduction of the promisc flag we still use brdev->flags & > IFF_PROMISC in br_pass_frame_up() which is essentially the value of > promisc (except in the BR_FDB_LOCAL case above) instead of promisc > itself. > > Amedeo > > [snip] Please don't top post on netdev@. The current code works correctly, my question to Pablo was more about if the warn can still be triggered by adding a BR_FDB_LOCAL fdb and setting bridge promisc on, then we'll hit that codepath with promisc == false and it's kind of correct because traffic would've been passed up anyway, but the promisc flag can be actually set on the device.. Cheers, Nik
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