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ip: fix IP_CHECKSUM handling

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The skbs processed by ip_cmsg_recv() are not guaranteed to
be linear e.g. when sending UDP packets over loopback with
MSGMORE.
Using csum_partial() on [potentially] the whole skb len
is dangerous; instead be on the safe side and use skb_checksum().

Thanks to syzkaller team to detect the issue and provide the
reproducer.

v1 -> v2:
 - move the variable declaration in a tighter scope

Fixes: ad6f939ab1 ("ip: Add offset parameter to ip_cmsg_recv")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni 2017-02-21 09:33:18 +01:00 committed by David S. Miller
parent 8dcd81a993
commit ca4ef4574f
1 changed files with 4 additions and 4 deletions
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8
net/ipv4/ip_sockglue.c
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@ -116,10 +116,10 @@ static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb,
if (skb->ip_summed != CHECKSUM_COMPLETE)
return;
if (offset != 0)
csum = csum_sub(csum,
csum_partial(skb_transport_header(skb) + tlen,
offset, 0));
if (offset != 0) {
int tend_off = skb_transport_offset(skb) + tlen;
csum = csum_sub(csum, skb_checksum(skb, tend_off, offset, 0));
}
put_cmsg(msg, SOL_IP, IP_CHECKSUM, sizeof(__wsum), &csum);
}