Commit 31c2e492 authored by Willem de Bruijn's avatar Willem de Bruijn Committed by David S. Miller

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 e6afc8ac 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: e6afc8ac ("udp: remove headers from UDP packets before queueing")
Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9f9a45be
...@@ -106,7 +106,8 @@ static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb, ...@@ -106,7 +106,8 @@ static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb,
return; return;
if (offset != 0) 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); put_cmsg(msg, SOL_IP, IP_CHECKSUM, sizeof(__wsum), &csum);
} }
......
...@@ -1375,7 +1375,7 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock, ...@@ -1375,7 +1375,7 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
*addr_len = sizeof(*sin); *addr_len = sizeof(*sin);
} }
if (inet->cmsg_flags) 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; err = copied;
if (flags & MSG_TRUNC) if (flags & MSG_TRUNC)
......
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