packet-solutions: Fix checksum folding helper

tohojo · tohojo · commit f023ad962ed0 · 2020-09-28T19:12:16.000+02:00
As reported by @mwiget - the csum_fold_helper() was missing a round of folding. Fixes #130. Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
diff --git a/packet-solutions/xdp_prog_kern_03.c b/packet-solutions/xdp_prog_kern_03.c
@@ -32,7 +32,10 @@ struct bpf_map_def SEC("maps") redirect_params = {
 
 static __always_inline __u16 csum_fold_helper(__u32 csum)
 {
-	return ~((csum & 0xffff) + (csum >> 16));
+	__u32 sum;
+	sum = (csum >> 16) + (csum & 0xffff);
+	sum += (sum >> 16);
+	return ~sum;
 }
 
 /*

Original file line number	Diff line number	Diff line change
`@@ -32,7 +32,10 @@ struct bpf_map_def SEC("maps") redirect_params = {`
`32`	`32`
`33`	`33`	`static __always_inline __u16 csum_fold_helper(__u32 csum)`
`34`	`34`	`{`
`35`		`- return ~((csum & 0xffff) + (csum >> 16));`
	`35`	`+ __u32 sum;`
	`36`	`+ sum = (csum >> 16) + (csum & 0xffff);`
	`37`	`+ sum += (sum >> 16);`
	`38`	`+ return ~sum;`
`36`	`39`	`}`
`37`	`40`
`38`	`41`	`/*`