Re: [PATCH v4 net-next] net:sched: add action inheritdsfield to skbedit

The new action inheritdsfield copies the field DS of
IPv4 and IPv6 packets into skb->priority. This enables
later classification of packets based on the DS field.

v4:
*Not allow setting flags other than the expected ones.

*Allow dumping the pure flags.

Original idea by Jamal Hadi Salim [off-list ref]

Signed-off-by: Qiaobin Fu <redacted>
Reviewed-by: Michel Machado <redacted>
---

Note that the motivation for this patch is found in the following discussion:
https://www.spinics.net/lists/netdev/msg501061.html
---

diff --git a/include/uapi/linux/tc_act/tc_skbedit.h b/include/uapi/linux/tc_act/tc_skbedit.h
index fbcfe27a4e6c..6de6071ebed6 100644
--- a/include/uapi/linux/tc_act/tc_skbedit.h
+++ b/include/uapi/linux/tc_act/tc_skbedit.h

@@ -30,6 +30,7 @@
  #define SKBEDIT_F_MARK			0x4
  #define SKBEDIT_F_PTYPE			0x8
  #define SKBEDIT_F_MASK			0x10
+#define SKBEDIT_F_INHERITDSFIELD	0x20
  
  struct tc_skbedit {
  	tc_gen;

@@ -45,6 +46,7 @@ enum {
  	TCA_SKBEDIT_PAD,
  	TCA_SKBEDIT_PTYPE,
  	TCA_SKBEDIT_MASK,
+	TCA_SKBEDIT_FLAGS,
  	__TCA_SKBEDIT_MAX
  };
  #define TCA_SKBEDIT_MAX (__TCA_SKBEDIT_MAX - 1)

diff --git a/net/sched/act_skbedit.c b/net/sched/act_skbedit.c
index 6138d1d71900..9adbcfa3f5fe 100644
--- a/net/sched/act_skbedit.c
+++ b/net/sched/act_skbedit.c

@@ -23,6 +23,9 @@
  #include <linux/rtnetlink.h>
  #include <net/netlink.h>
  #include <net/pkt_sched.h>
+#include <net/ip.h>
+#include <net/ipv6.h>
+#include <net/dsfield.h>
  
  #include <linux/tc_act/tc_skbedit.h>
  #include <net/tc_act/tc_skbedit.h>

@@ -41,6 +44,25 @@ static int tcf_skbedit(struct sk_buff *skb, const struct tc_action *a,
  
  	if (d->flags & SKBEDIT_F_PRIORITY)
  		skb->priority = d->priority;
+	if (d->flags & SKBEDIT_F_INHERITDSFIELD) {
+		int wlen = skb_network_offset(skb);
+
+		switch (tc_skb_protocol(skb)) {
+		case htons(ETH_P_IP):
+			wlen += sizeof(struct iphdr);
+			if (!pskb_may_pull(skb, wlen))
+				goto err;
+			skb->priority = ipv4_get_dsfield(ip_hdr(skb)) >> 2;
+			break;
+
+		case htons(ETH_P_IPV6):
+			wlen += sizeof(struct ipv6hdr);
+			if (!pskb_may_pull(skb, wlen))
+				goto err;
+			skb->priority = ipv6_get_dsfield(ipv6_hdr(skb)) >> 2;
+			break;
+		}
+	}
  	if (d->flags & SKBEDIT_F_QUEUE_MAPPING &&
  	    skb->dev->real_num_tx_queues > d->queue_mapping)
  		skb_set_queue_mapping(skb, d->queue_mapping);

@@ -53,6 +75,10 @@ static int tcf_skbedit(struct sk_buff *skb, const struct tc_action *a,
  
  	spin_unlock(&d->tcf_lock);
  	return d->tcf_action;
+
+err:
+	spin_unlock(&d->tcf_lock);
+	return TC_ACT_SHOT;
  }
  
  static const struct nla_policy skbedit_policy[TCA_SKBEDIT_MAX + 1] = {

@@ -62,6 +88,7 @@ static const struct nla_policy skbedit_policy[TCA_SKBEDIT_MAX + 1] = {
  	[TCA_SKBEDIT_MARK]		= { .len = sizeof(u32) },
  	[TCA_SKBEDIT_PTYPE]		= { .len = sizeof(u16) },
  	[TCA_SKBEDIT_MASK]		= { .len = sizeof(u32) },
+	[TCA_SKBEDIT_FLAGS]		= { .len = sizeof(u64) },
  };
  
  static int tcf_skbedit_init(struct net *net, struct nlattr *nla,

@@ -73,6 +100,7 @@ static int tcf_skbedit_init(struct net *net, struct nlattr *nla,
  	struct tc_skbedit *parm;
  	struct tcf_skbedit *d;
  	u32 flags = 0, *priority = NULL, *mark = NULL, *mask = NULL;
+	u64 *pure_flags = NULL;
  	u16 *queue_mapping = NULL, *ptype = NULL;
  	bool exists = false;
  	int ret = 0, err;

@@ -114,6 +142,12 @@ static int tcf_skbedit_init(struct net *net, struct nlattr *nla,
  		mask = nla_data(tb[TCA_SKBEDIT_MASK]);
  	}
  
+	if (tb[TCA_SKBEDIT_FLAGS] != NULL) {
+		pure_flags = nla_data(tb[TCA_SKBEDIT_FLAGS]);
+		if (*pure_flags & SKBEDIT_F_INHERITDSFIELD)
+			flags |= SKBEDIT_F_INHERITDSFIELD;
+	}
+
  	parm = nla_data(tb[TCA_SKBEDIT_PARMS]);
  
  	exists = tcf_idr_check(tn, parm->index, a, bind);

@@ -178,6 +212,7 @@ static int tcf_skbedit_dump(struct sk_buff *skb, struct tc_action *a,
  		.action  = d->tcf_action,
  	};
  	struct tcf_t t;
+	u64 pure_flags = 0;
  
  	if (nla_put(skb, TCA_SKBEDIT_PARMS, sizeof(opt), &opt))
  		goto nla_put_failure;

@@ -196,6 +231,11 @@ static int tcf_skbedit_dump(struct sk_buff *skb, struct tc_action *a,
  	if ((d->flags & SKBEDIT_F_MASK) &&
  	    nla_put_u32(skb, TCA_SKBEDIT_MASK, d->mask))
  		goto nla_put_failure;
+	if (d->flags & SKBEDIT_F_INHERITDSFIELD)
+		pure_flags |= SKBEDIT_F_INHERITDSFIELD;
+	if (pure_flags != 0 &&
+	    nla_put(skb, TCA_SKBEDIT_FLAGS, sizeof(pure_flags), &pure_flags))
+		goto nla_put_failure;
  
  	tcf_tm_dump(&t, &d->tcf_tm);
  	if (nla_put_64bit(skb, TCA_SKBEDIT_TM, sizeof(t), &t, TCA_SKBEDIT_PAD))