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[PATCH 4.10 02/21] ip: fix IP_CHECKSUM handling

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4.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paolo Abeni <pabeni@redhat.com>


[ Upstream commit ca4ef4574f1ee5252e2cd365f8f5d5bafd048f32 ]

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: ad6f939ab193 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/ip_sockglue.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -116,10 +116,10 @@ static void ip_cmsg_recv_checksum(struct
 	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);
 }

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[PATCH 4.10 00/21] 4.10.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 13/21] USB: serial: ark3116: fix register-accessor error handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 06/21] USB: serial: cp210x: add new IDs for GE Bx50v3 boards Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 10/21] USB: serial: digi_acceleport: fix OOB data sanity check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 16/21] goldfish: Sanitize the broken interrupt handler Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 20/21] rtlwifi: rtl_usb: Fix for URB leaking when doing ifconfig up/down Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 14/21] USB: serial: console: fix uninitialised spinlock Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 04/21] tty: serial: msm: Fix module autoload Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 15/21] x86/platform/goldfish: Prevent unconditional loading Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 02/21] ip: fix IP_CHECKSUM handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 17/21] netfilter: nf_ct_helper: warn when not applying default helper assignment Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 12/21] USB: serial: opticon: fix CTS retrieval at open Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 05/21] USB: serial: mos7840: fix another NULL-deref at open Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  [PATCH 4.10 19/21] block: fix double-free in the failure path of cgwb_bdi_init() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:50 +0100
  Re: [PATCH 4.10 00/21] 4.10.1-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-02-24 19:40 +0100
    Re: [PATCH 4.10 00/21] 4.10.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-26 17:10 +0100
  Re: [PATCH 4.10 00/21] 4.10.1-stable review Guenter Roeck <linux@roeck-us.net> - 2017-02-25 05:30 +0100
    Re: [PATCH 4.10 00/21] 4.10.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-26 17:10 +0100
  Re: [PATCH 4.10 00/21] 4.10.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-26 17:10 +0100
    Re: [PATCH 4.10 00/21] 4.10.1-stable review Kevin Hilman <khilman@baylibre.com> - 2017-02-27 21:30 +0100

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