[dpdk-dev] [PATCH 1/2] net: fix underflow for checksum of invalid IPv4 packets

[Bruce Richardson]

If we receive a packet with an invalid IP header, where the total packet
length is reported as less than the IP header length, we would end up
getting an underflow in the length subtraction. This could cause us to
checksum e.g. 4GB of data in the case where the result of the subtraction
was -1. We fix this by having the function return 0 - an invalid sum - when
the length is less than the header length.

CC: stable at dpdk.org
Fixes: af75078fece3 ("first public release")
Fixes: 6006818cfb26 ("net: new checksum functions")

Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
---
 lib/librte_net/rte_ip.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
index f2a8904a2..f9b909090 100644
--- a/lib/librte_net/rte_ip.h
+++ b/lib/librte_net/rte_ip.h
@@ -310,16 +310,20 @@ rte_ipv4_phdr_cksum(const struct ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
  * @param l4_hdr
  *   The pointer to the beginning of the L4 header.
  * @return
- *   The complemented checksum to set in the IP packet.
+ *   The complemented checksum to set in the IP packet
+ *   or 0 on error
  */
 static inline uint16_t
 rte_ipv4_udptcp_cksum(const struct ipv4_hdr *ipv4_hdr, const void *l4_hdr)
 {
 	uint32_t cksum;
-	uint32_t l4_len;
+	uint32_t l3_len, l4_len;
+
+	l3_len = rte_be_to_cpu_16(ipv4_hdr->total_length);
+	if (l3_len < sizeof(struct ipv4_hdr))
+		return 0;
 
-	l4_len = (uint32_t)(rte_be_to_cpu_16(ipv4_hdr->total_length) -
-		sizeof(struct ipv4_hdr));
+	l4_len = l3_len - sizeof(struct ipv4_hdr);
 
 	cksum = rte_raw_cksum(l4_hdr, l4_len);
 	cksum += rte_ipv4_phdr_cksum(ipv4_hdr, 0);
-- 
2.19.2