From: Willem de Bruijn Date: Thu, 7 Apr 2016 22:12:59 +0000 (-0400) Subject: udp: do not expect udp headers in recv cmsg IP_CMSG_CHECKSUM X-Git-Tag: v4.7-rc1~154^2~304^2 X-Git-Url: http://git.cascardo.info/?p=cascardo%2Flinux.git;a=commitdiff_plain;h=31c2e4926fe912f88388bcaa8450fcaa8f2ece47 udp: do not expect udp headers in recv cmsg IP_CMSG_CHECKSUM On udp sockets, recv cmsg IP_CMSG_CHECKSUM returns a checksum over the packet payload. Since commit e6afc8ace6dd pulled the headers, taking skb->data as the start of transport header is incorrect. Use the transport header pointer. Also, when peeking at an offset from the start of the packet, only return a checksum from the start of the peeked data. Note that the cmsg does not subtract a tail checkum when reading truncated data. Fixes: e6afc8ace6dd ("udp: remove headers from UDP packets before queueing") Signed-off-by: Willem de Bruijn Signed-off-by: David S. Miller --- diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c index 89b5f3bd6694..279471c4e58f 100644 --- a/net/ipv4/ip_sockglue.c +++ b/net/ipv4/ip_sockglue.c @@ -106,7 +106,8 @@ static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb, return; if (offset != 0) - csum = csum_sub(csum, csum_partial(skb->data, offset, 0)); + csum = csum_sub(csum, csum_partial(skb_transport_header(skb), + offset, 0)); put_cmsg(msg, SOL_IP, IP_CHECKSUM, sizeof(__wsum), &csum); } diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index d2d294b0a1f1..f1863136d3e4 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1375,7 +1375,7 @@ try_again: *addr_len = sizeof(*sin); } if (inet->cmsg_flags) - ip_cmsg_recv_offset(msg, skb, sizeof(struct udphdr)); + ip_cmsg_recv_offset(msg, skb, sizeof(struct udphdr) + off); err = copied; if (flags & MSG_TRUNC)