Subject: [PATCH 03/12] net: create skb_gso_validate_mac_len()

From: Daniel Axtens <[email-masked]>
Date: Wed, 31 Jan 2018 14:15:33 +1100

commit 2b16f048729bf35e6c28a40cbfad07239f9dcd90 upstream.

If you take a GSO skb, and split it into packets, will the MAC
length (L2 + L3 + L4 headers + payload) of those packets be small
enough to fit within a given length?

Move skb_gso_mac_seglen() to skbuff.h with other related functions
like skb_gso_network_seglen() so we can use it, and then create
skb_gso_validate_mac_len to do the full calculation.

Signed-off-by: Daniel Axtens <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
[bwh: Backported to 4.4: There is no GSO_BY_FRAGS case to handle, so
 skb_gso_validate_mac_len() becomes a trivial comparison. Put it inline in
 <linux/skbuff.h>.]
Signed-off-by: Ben Hutchings <[email-masked]>
---
 include/linux/skbuff.h | 30 ++++++++++++++++++++++++++++++
 net/sched/sch_tbf.c    | 10 ----------
 2 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 502787c29ce9..a2f12d377d23 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3664,5 +3664,35 @@ static inline unsigned int skb_gso_network_seglen(const struct sk_buff *skb)
 	return hdr_len + skb_gso_transport_seglen(skb);
 }
 
+/**
+ * skb_gso_mac_seglen - Return length of individual segments of a gso packet
+ *
+ * @skb: GSO skb
+ *
+ * skb_gso_mac_seglen is used to determine the real size of the
+ * individual segments, including MAC/L2, Layer3 (IP, IPv6) and L4
+ * headers (TCP/UDP).
+ */
+static inline unsigned int skb_gso_mac_seglen(const struct sk_buff *skb)
+{
+	unsigned int hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
+	return hdr_len + skb_gso_transport_seglen(skb);
+}
+
+/**
+ * skb_gso_validate_mac_len - Will a split GSO skb fit in a given length?
+ *
+ * @skb: GSO skb
+ * @len: length to validate against
+ *
+ * skb_gso_validate_mac_len validates if a given skb will fit a wanted
+ * length once split, including L2, L3 and L4 headers and the payload.
+ */
+static inline bool
+skb_gso_validate_mac_len(const struct sk_buff *skb, unsigned int len)
+{
+	return skb_gso_mac_seglen(skb) <= len;
+}
+
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_SKBUFF_H */
diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index a06c9d6bfc9c..05c7a66f64da 100644
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -142,16 +142,6 @@ static u64 psched_ns_t2l(const struct psched_ratecfg *r,
 	return len;
 }
 
-/*
- * Return length of individual segments of a gso packet,
- * including all headers (MAC, IP, TCP/UDP)
- */
-static unsigned int skb_gso_mac_seglen(const struct sk_buff *skb)
-{
-	unsigned int hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
-	return hdr_len + skb_gso_transport_seglen(skb);
-}
-
 /* GSO packet is too big, segment it so that tbf can transmit
  * each segment in time
  */
-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom