Re: [PATCH v2,net-next 1/2] ip_gre: fix parsing gre header in ipgre_err

On 2018年9月14日, at 上午1:58, David Miller [off-list ref] wrote:

From: Haishuang Yan <redacted>
Date: Wed, 12 Sep 2018 17:21:21 +0800

quoted

@@ -86,7 +86,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,

	options = (__be32 *)(greh + 1);
	if (greh->flags & GRE_CSUM) {
-		if (skb_checksum_simple_validate(skb)) {
+		if (csum_err && skb_checksum_simple_validate(skb)) {
			*csum_err = true;
			return -EINVAL;
		}

You want to ignore csum errors, but you do not want to elide the side
effects of the skb_checksum_simple_validate() call which are to set
skb->csum_valid and skb->csum.

Therefore, the skb_checksum_simple_validate() call still needs to be
performed. We just wont return -EINVAL in the NULL csum_err case.

How about doing like this:

--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c

@@ -86,13 +86,14 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,

        options = (__be32 *)(greh + 1);
        if (greh->flags & GRE_CSUM) {
-               if (skb_checksum_simple_validate(skb)) {
+               if (!skb_checksum_simple_validate(skb)) {
+                       skb_checksum_try_convert(skb, IPPROTO_GRE, 0,
+                                                null_compute_pseudo);
+               } else if (csum_err) {
                        *csum_err = true;
                        return -EINVAL;
                }

-               skb_checksum_try_convert(skb, IPPROTO_GRE, 0,
-                                        null_compute_pseudo);

Thanks for reviewing.