udp: Remove partial csum code in RX.

UDP-Lite supports the partial checksum and the coverage is
stored in the position of the length field of struct udphdr.

In RX paths, udp4_csum_init() / udp6_csum_init() save the value
in UDP_SKB_CB(skb)->cscov and set UDP_SKB_CB(skb)->partial_cov
to 1 if the coverage is not full.

The subsequent processing diverges depending on the value,
but such paths are now dead.

Also, these functions have some code guarded for UDP:

  * udp_unicast_rcv_skb / udp6_unicast_rcv_skb
  * __udp4_lib_rcv() and __udp6_lib_rcv().

Let's remove the partial csum code and the unnecessary
guard for UDP-Lite in RX.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260311052020.1213705-8-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 3 insertions, 48 deletions

diff --git a/include/net/udp.h b/include/net/udp.h
index 264c10607d2e..bc275cda9f8c 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -32,11 +32,9 @@
 #include <linux/math.h>
 
 /**
- *	struct udp_skb_cb  -  UDP(-Lite) private variables
+ *	struct udp_skb_cb  -  UDP private variables
  *
  *	@header:      private variables used by IPv4/IPv6
- *	@cscov:       checksum coverage length (UDP-Lite only)
- *	@partial_cov: if set indicates partial csum coverage
  */
 struct udp_skb_cb {
 	union {
@@ -45,8 +43,6 @@ struct udp_skb_cb {
 		struct inet6_skb_parm	h6;
 #endif
 	} header;
-	__u16		cscov;
-	__u8		partial_cov;
 };
 #define UDP_SKB_CB(__skb)	((struct udp_skb_cb *)((__skb)->cb))
 
@@ -216,13 +212,11 @@ extern int sysctl_udp_wmem_min;
 struct sk_buff;
 
 /*
- *	Generic checksumming routines for UDP(-Lite) v4 and v6
+ *	Generic checksumming routines for UDP v4 and v6
  */
 static inline __sum16 __udp_lib_checksum_complete(struct sk_buff *skb)
 {
-	return (UDP_SKB_CB(skb)->cscov == skb->len ?
-		__skb_checksum_complete(skb) :
-		__skb_checksum_complete_head(skb, UDP_SKB_CB(skb)->cscov));
+	return __skb_checksum_complete(skb);
 }
 
 static inline int udp_lib_checksum_complete(struct sk_buff *skb)
@@ -273,7 +267,6 @@ static inline void udp_csum_pull_header(struct sk_buff *skb)
 		skb->csum = csum_partial(skb->data, sizeof(struct udphdr),
 					 skb->csum);
 	skb_pull_rcsum(skb, sizeof(struct udphdr));
-	UDP_SKB_CB(skb)->cscov -= sizeof(struct udphdr);
 }
 
 typedef struct sock *(*udp_lookup_t)(const struct sk_buff *skb, __be16 sport,
@@ -641,9 +634,6 @@ drop:
 
 static inline void udp_post_segment_fix_csum(struct sk_buff *skb)
 {
-	/* UDP-lite can't land here - no GRO */
-	WARN_ON_ONCE(UDP_SKB_CB(skb)->partial_cov);
-
 	/* UDP packets generated with UDP_SEGMENT and traversing:
 	 *
 	 * UDP tunnel(xmit) -> veth (segmentation) -> veth (gro) -> UDP tunnel (rx)
@@ -657,7 +647,6 @@ static inline void udp_post_segment_fix_csum(struct sk_buff *skb)
 	 * a valid csum after the segmentation.
 	 * Additionally fixup the UDP CB.
 	 */
-	UDP_SKB_CB(skb)->cscov = skb->len;
 	if (skb->ip_summed == CHECKSUM_NONE && !skb->csum_valid)
 		skb->csum_valid = 1;
 }
diff --git a/include/net/udplite.h b/include/net/udplite.h
index fdd769745ac4..0456a14c993b 100644
--- a/include/net/udplite.h
+++ b/include/net/udplite.h
@@ -25,40 +25,6 @@ static __inline__ int udplite_getfrag(void *from, char *to, int  offset,
 /*
  * 	Checksumming routines
  */
-static inline int udplite_checksum_init(struct sk_buff *skb, struct udphdr *uh)
-{
-	u16 cscov;
-
-        /* In UDPv4 a zero checksum means that the transmitter generated no
-         * checksum. UDP-Lite (like IPv6) mandates checksums, hence packets
-         * with a zero checksum field are illegal.                            */
-	if (uh->check == 0) {
-		net_dbg_ratelimited("UDPLite: zeroed checksum field\n");
-		return 1;
-	}
-
-	cscov = ntohs(uh->len);
-
-	if (cscov == 0)		 /* Indicates that full coverage is required. */
-		;
-	else if (cscov < 8  || cscov > skb->len) {
-		/*
-		 * Coverage length violates RFC 3828: log and discard silently.
-		 */
-		net_dbg_ratelimited("UDPLite: bad csum coverage %d/%d\n",
-				    cscov, skb->len);
-		return 1;
-
-	} else if (cscov < skb->len) {
-        	UDP_SKB_CB(skb)->partial_cov = 1;
-		UDP_SKB_CB(skb)->cscov = cscov;
-		if (skb->ip_summed == CHECKSUM_COMPLETE)
-			skb->ip_summed = CHECKSUM_NONE;
-		skb->csum_valid = 0;
-        }
-
-	return 0;
-}
 
 /* Fast-path computation of checksum. Socket may not be locked. */
 static inline __wsum udplite_csum(struct sk_buff *skb)