netfilter: nft_payload: mangle ckecksum if NFT_PAYLOAD_L4CSUM_PSEUDOHDR is set

If the NFT_PAYLOAD_L4CSUM_PSEUDOHDR flag is set, then mangle layer 4
checksum. This should not depend on csum_type NFT_PAYLOAD_CSUM_INET
since IPv6 header has no checksum field, but still an update of any of
the pseudoheader fields may trigger a layer 4 checksum update.

Fixes: 18140969 ("netfilter: nft_payload: layer 4 checksum adjustment for pseudoheader fields")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_payload.c

@@ -250,6 +250,22 @@ static int nft_payload_l4csum_update(const struct nft_pktinfo *pkt,
 	return 0;
 }
 
+static int nft_payload_csum_inet(struct sk_buff *skb, const u32 *src,
+				 __wsum fsum, __wsum tsum, int csum_offset)
+{
+	__sum16 sum;
+
+	if (skb_copy_bits(skb, csum_offset, &sum, sizeof(sum)) < 0)
+		return -1;
+
+	nft_csum_replace(&sum, fsum, tsum);
+	if (!skb_make_writable(skb, csum_offset + sizeof(sum)) ||
+	    skb_store_bits(skb, csum_offset, &sum, sizeof(sum)) < 0)
+		return -1;
+
+	return 0;
+}
+
 static void nft_payload_set_eval(const struct nft_expr *expr,
 				 struct nft_regs *regs,
 				 const struct nft_pktinfo *pkt)
@@ -259,7 +275,6 @@ static void nft_payload_set_eval(const struct nft_expr *expr,
 	const u32 *src = &regs->data[priv->sreg];
 	int offset, csum_offset;
 	__wsum fsum, tsum;
-	__sum16 sum;
 
 	switch (priv->base) {
 	case NFT_PAYLOAD_LL_HEADER:
@@ -282,18 +297,14 @@ static void nft_payload_set_eval(const struct nft_expr *expr,
 	csum_offset = offset + priv->csum_offset;
 	offset += priv->offset;
 
-	if (priv->csum_type == NFT_PAYLOAD_CSUM_INET &&
+	if ((priv->csum_type == NFT_PAYLOAD_CSUM_INET || priv->csum_flags) &&
 	    (priv->base != NFT_PAYLOAD_TRANSPORT_HEADER ||
 	     skb->ip_summed != CHECKSUM_PARTIAL)) {
-		if (skb_copy_bits(skb, csum_offset, &sum, sizeof(sum)) < 0)
-			goto err;
-
 		fsum = skb_checksum(skb, offset, priv->len, 0);
 		tsum = csum_partial(src, priv->len, 0);
-		nft_csum_replace(&sum, fsum, tsum);
 
-		if (!skb_make_writable(skb, csum_offset + sizeof(sum)) ||
-		    skb_store_bits(skb, csum_offset, &sum, sizeof(sum)) < 0)
+		if (priv->csum_type == NFT_PAYLOAD_CSUM_INET &&
+		    nft_payload_csum_inet(skb, src, fsum, tsum, csum_offset))
 			goto err;
 
 		if (priv->csum_flags &&