From fab01a6f3a61748b9c2e038c84498c6624b06236 Mon Sep 17 00:00:00 2001 From: Alex Elder Date: Sat, 12 Jun 2021 09:37:32 -0500 Subject: 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: Alex Elder Signed-off-by: David S. Miller --- .../net/ethernet/qualcomm/rmnet/rmnet_map_data.c | 36 ++++++++++++++++------ 1 file changed, 27 insertions(+), 9 deletions(-) (limited to 'drivers/net/ethernet/qualcomm/rmnet') diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c index 51909b8fa8a8..a05124eb8602 100644 --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c @@ -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)) { -- cgit v1.2.3-59-g8ed1b