Re: [PATCH net] ip: fix IP_CHECKSUM handling
On Mon, 20 Feb 2017 17:55:39 +0100 Paolo Abeniwrote: > 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. > > Fixes: ad6f939ab193 ("ip: Add offset parameter to ip_cmsg_recv") > Reported-by: Andrey Konovalov > Signed-off-by: Paolo Abeni > --- > net/ipv4/ip_sockglue.c | 9 + > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c > index 9000117..d88bbe2 100644 > --- a/net/ipv4/ip_sockglue.c > +++ b/net/ipv4/ip_sockglue.c > @@ -112,14 +112,15 @@ static void ip_cmsg_recv_checksum(struct msghdr *msg, > struct sk_buff *skb, > int tlen, int offset) > { > __wsum csum = skb->csum; > + int tend_off; > > 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) { > + tend_off = skb_transport_offset(skb) + tlen; > + csum = csum_sub(csum, skb_checksum(skb, tend_off, offset, 0)); > + } If you need to add a local variable (tend_off) then please make its scope as tight as possible. i.e. if (offset != 0) { int tend_off = skb_transport_offset(skb) + tlen;
[PATCH net] ip: fix IP_CHECKSUM handling
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. Fixes: ad6f939ab193 ("ip: Add offset parameter to ip_cmsg_recv") Reported-by: Andrey KonovalovSigned-off-by: Paolo Abeni --- net/ipv4/ip_sockglue.c | 9 + 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c index 9000117..d88bbe2 100644 --- a/net/ipv4/ip_sockglue.c +++ b/net/ipv4/ip_sockglue.c @@ -112,14 +112,15 @@ static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb, int tlen, int offset) { __wsum csum = skb->csum; + int tend_off; 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) { + 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), ); } -- 2.9.3