ipv6: rpl: Remove pskb(_may)?_pull() in ipv6_rpl_srh_rcv().

As Eric Dumazet pointed out [0], ipv6_rthdr_rcv() pulls these data

- Segment Routing Header : 8
- Hdr Ext Len : skb_transport_header(skb)[1] << 3

needed by ipv6_rpl_srh_rcv(). We can remove pskb_may_pull() and
replace pskb_pull() with skb_pull() in ipv6_rpl_srh_rcv().

Link: https://lore.kernel.org/netdev/[e-mail]/ [0]
Signed-off-by: Kuniyuki Iwashima <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/rpl.h

···
 static inline void rpl_exit(void) {}
 #endif
 
-size_t ipv6_rpl_srh_size(unsigned char n, unsigned char cmpri,
-			 unsigned char cmpre);
-
 void ipv6_rpl_srh_decompress(struct ipv6_rpl_sr_hdr *outhdr,
 			     const struct ipv6_rpl_sr_hdr *inhdr,
 			     const struct in6_addr *daddr, unsigned char n);

net/ipv6/exthdrs.c

···
 
 			skb_postpull_rcsum(skb, skb_network_header(skb),
 					   skb_network_header_len(skb));
-
-			if (!pskb_pull(skb, offset)) {
-				kfree_skb(skb);
-				return -1;
-			}
+			skb_pull(skb, offset);
 			skb_postpull_rcsum(skb, skb_transport_header(skb),
 					   offset);
 
···
 		return 1;
 	}
 
-	if (!pskb_may_pull(skb, sizeof(*hdr))) {
-		kfree_skb(skb);
-		return -1;
-	}
-
 	n = (hdr->hdrlen << 3) - hdr->pad - (16 - hdr->cmpre);
 	r = do_div(n, (16 - hdr->cmpri));
 	/* checks if calculation was without remainder and n fits into
···
 		icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
 				  ((&hdr->segments_left) -
 				   skb_network_header(skb)));
-		return -1;
-	}
-
-	if (!pskb_may_pull(skb, ipv6_rpl_srh_size(n, hdr->cmpri,
-						  hdr->cmpre))) {
-		kfree_skb(skb);
 		return -1;
 	}
 

net/ipv6/rpl.c

···
 	return (void *)&hdr->rpl_segdata[i * IPV6_PFXTAIL_LEN(hdr->cmpri)];
 }
 
-size_t ipv6_rpl_srh_size(unsigned char n, unsigned char cmpri,
-			 unsigned char cmpre)
-{
-	return sizeof(struct ipv6_rpl_sr_hdr) + (n * IPV6_PFXTAIL_LEN(cmpri)) +
-		IPV6_PFXTAIL_LEN(cmpre);
-}
-
 void ipv6_rpl_srh_decompress(struct ipv6_rpl_sr_hdr *outhdr,
 			     const struct ipv6_rpl_sr_hdr *inhdr,
 			     const struct in6_addr *daddr, unsigned char n)