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Message-ID: <f7t5xz1k5h4.fsf@redhat.com>
Date: Tue, 06 Feb 2024 09:55:03 -0500
From: Aaron Conole <aconole@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, Jakub
Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Pravin B
Shelar <pshelar@....org>, dev@...nvswitch.org, Ilya Maximets
<i.maximets@....org>, Simon Horman <horms@....org>, Eelco Chaudron
<echaudro@...hat.com>
Subject: Re: [PATCH net 1/2] net: openvswitch: limit the number of
recursions from action sets
Eric Dumazet <edumazet@...gle.com> writes:
> On Tue, Feb 6, 2024 at 2:11 PM Aaron Conole <aconole@...hat.com> wrote:
>>
>> The ovs module allows for some actions to recursively contain an action
>> list for complex scenarios, such as sampling, checking lengths, etc.
>> When these actions are copied into the internal flow table, they are
>> evaluated to validate that such actions make sense, and these calls
>> happen recursively.
>>
>> The ovs-vswitchd userspace won't emit more than 16 recursion levels
>> deep. However, the module has no such limit and will happily accept
>> limits larger than 16 levels nested. Prevent this by tracking the
>> number of recursions happening and manually limiting it to 16 levels
>> nested.
>>
>> The initial implementation of the sample action would track this depth
>> and prevent more than 3 levels of recursion, but this was removed to
>> support the clone use case, rather than limited at the current userspace
>> limit.
>>
>> Fixes: 798c166173ff ("openvswitch: Optimize sample action for the clone use cases")
>> Signed-off-by: Aaron Conole <aconole@...hat.com>
>> ---
>> net/openvswitch/flow_netlink.c | 33 ++++++++++++++++++++++++++++-----
>> 1 file changed, 28 insertions(+), 5 deletions(-)
>>
>> diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
>> index 88965e2068ac..ba5cfa67a720 100644
>> --- a/net/openvswitch/flow_netlink.c
>> +++ b/net/openvswitch/flow_netlink.c
>> @@ -48,6 +48,9 @@ struct ovs_len_tbl {
>>
>> #define OVS_ATTR_NESTED -1
>> #define OVS_ATTR_VARIABLE -2
>> +#define OVS_COPY_ACTIONS_MAX_DEPTH 16
>> +
>> +static DEFINE_PER_CPU(int, copy_actions_depth);
>>
>> static bool actions_may_change_flow(const struct nlattr *actions)
>> {
>> @@ -3148,11 +3151,11 @@ static int copy_action(const struct nlattr *from,
>> return 0;
>> }
>>
>> -static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
>> - const struct sw_flow_key *key,
>> - struct sw_flow_actions **sfa,
>> - __be16 eth_type, __be16 vlan_tci,
>> - u32 mpls_label_count, bool log)
>> +static int ___ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
>> + const struct sw_flow_key *key,
>> + struct sw_flow_actions **sfa,
>> + __be16 eth_type, __be16 vlan_tci,
>> + u32 mpls_label_count, bool log)
>> {
>> u8 mac_proto = ovs_key_mac_proto(key);
>> const struct nlattr *a;
>> @@ -3478,6 +3481,26 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
>> return 0;
>> }
>>
>> +static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
>> + const struct sw_flow_key *key,
>> + struct sw_flow_actions **sfa,
>> + __be16 eth_type, __be16 vlan_tci,
>> + u32 mpls_label_count, bool log)
>> +{
>> + int level = this_cpu_read(copy_actions_depth);
>> + int ret;
>> +
>> + if (level > OVS_COPY_ACTIONS_MAX_DEPTH)
>> + return -EOVERFLOW;
>> +
>
> This code seems to run in process context.
>
> Using per cpu limit would not work, unless you disabled migration ?
Oops - I didn't consider it.
Given that, maybe the best approach would not to rely on per-cpu
counter. I'll respin in the next series with a depth counter that I pass
to the function instead and compare that. I guess that should address
migration and eliminate the need for per-cpu counter.
Does it make sense?
>> + __this_cpu_inc(copy_actions_depth);
>> + ret = ___ovs_nla_copy_actions(net, attr, key, sfa, eth_type,
>> + vlan_tci, mpls_label_count, log);
>> + __this_cpu_dec(copy_actions_depth);
>> +
>> + return ret;
>> +}
>> +
>> /* 'key' must be the masked key. */
>> int ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
>> const struct sw_flow_key *key,
>> --
>> 2.41.0
>>
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