Commit fab01a6f authored by Alex Elder's avatar Alex Elder Committed by David S. Miller
Browse files

net: qualcomm: rmnet: return earlier for bad checksum 



In rmnet_map_ipv4_dl_csum_trailer(), if the sum of the trailer
checksum and the pseudo checksum is non-zero, checksum validation
has failed.  We can return an error as soon as we know that.

We can do the same thing in rmnet_map_ipv6_dl_csum_trailer().

Add some comments that explain where we're headed.

Signed-off-by: default avatarAlex Elder <elder@linaro.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9d0407bc

drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c

+27 −9
Original line number Diff line number Diff line
@@ -76,6 +76,17 @@ rmnet_map_ipv4_dl_csum_trailer(struct sk_buff *skb, 
	 * We verified above that the IP header contributes zero to the

	 * trailer checksum.  Therefore the checksum in the trailer is

	 * just the checksum computed over the IP payload.



	 * If the IP payload arrives intact, adding the pseudo header

	 * checksum to the IP payload checksum will yield 0xffff (negative

	 * zero).  This means the trailer checksum and the pseudo checksum

	 * are additive inverses of each other.  Put another way, the

	 * message passes the checksum test if the trailer checksum value

	 * is the negated pseudo header checksum.

	 *

	 * Knowing this, we don't even need to examine the transport

	 * header checksum value; it is already accounted for in the

	 * checksum value found in the trailer.

	 */

	ip_payload_csum = (__force __sum16)~csum_trailer->csum_value;
@@ -84,11 +95,11 @@ rmnet_map_ipv4_dl_csum_trailer(struct sk_buff *skb, 
					 ip4h->protocol, 0);

	pseudo_csum = csum16_add(ip_payload_csum, (__force __be16)pseudo_csum);



	/* The trailer checksum *includes* the checksum in the transport

	 * header.  Adding that to the pseudo checksum will yield 0xffff

	 * ("negative 0") if the message arrived intact.

	 */

	WARN_ON((__sum16)~pseudo_csum);

	/* The cast is required to ensure only the low 16 bits are examined */

	if ((__sum16)~pseudo_csum) {

		priv->stats.csum_validation_failed++;

		return -EINVAL;

	}

	csum_value_final = ~csum16_sub(pseudo_csum, (__force __be16)*csum_field);



	if (unlikely(!csum_value_final)) {
@@ -143,6 +154,11 @@ rmnet_map_ipv6_dl_csum_trailer(struct sk_buff *skb, 
	 * transport checksum from this, we first subract the contribution

	 * of the IP header from the trailer checksum.  We then add the

	 * checksum computed over the pseudo header.

	 *

	 * It's sufficient to compare the IP payload checksum with the

	 * negated pseudo checksum to determine whether the packet

	 * checksum was good.  (See further explanation in comments

	 * in rmnet_map_ipv4_dl_csum_trailer()).

	 */

	ip_header_csum = (__force __be16)ip_fast_csum(ip6h, sizeof(*ip6h) / 4);

	ip6_payload_csum = ~csum16_sub((__force __sum16)csum_trailer->csum_value,
@@ -155,10 +171,12 @@ rmnet_map_ipv6_dl_csum_trailer(struct sk_buff *skb, 
				       length, ip6h->nexthdr, 0);

	pseudo_csum = csum16_add(ip6_payload_csum, (__force __be16)pseudo_csum);



	/* Adding the payload checksum to the pseudo checksum yields 0xffff

	 * ("negative 0") if the message arrived intact.

	 */

	WARN_ON((__sum16)~pseudo_csum);

	/* The cast is required to ensure only the low 16 bits are examined */

	if ((__sum16)~pseudo_csum) {

		priv->stats.csum_validation_failed++;

		return -EINVAL;

	}



	csum_value_final = ~csum16_sub(pseudo_csum, (__force __be16)*csum_field);



	if (unlikely(csum_value_final == 0)) {