Windows-host with disabled TX-checksum offloading may send
packets with tcp->checksum=0xffff. Most likely it is caused
by by Windows algorithm for computing incremental checksum
- see RFC 1624.
RFC1624 (sec.5) states that 0xffff and 0x0000 are equal, because
for example
0xCD7A + 0x3285 + 0xFFFF = 0xFFFF
0xCD7A + 0x3285 + 0x0000 = 0xFFFF;
Fix tcp/udp verification algorithm to check that checksum
of (transport-header + pseudo_hdr_csum) == 0
instead of recomputing checksum and comparing its value with
original value in transp_hdr->csum.
The problem could be reproduced on host linux network interface
without rx-offloading, because otherwise Guest-driver receives
from host packet with flag HDR_DATA_VALID
and VerifyTcpChecksum doesn't do any work.
---
NetKVM/Common/sw-offload.c | 46 ++++++++++++++++++++++++++-----------------
1 files changed, 28 insertions(+), 18 deletions(-)
diff --git a/NetKVM/Common/sw-offload.c b/NetKVM/Common/sw-offload.c
index 24acfdc..c8e1a39 100644
--- a/NetKVM/Common/sw-offload.c
+++ b/NetKVM/Common/sw-offload.c
@@ -372,6 +372,7 @@ static __inline tTcpIpPacketParsingResult
VerifyTcpChecksum( IPHeader *pIpHeader, ULONG len, tTcpIpPacketParsingResult known, ULONG whatToFix)
{
USHORT phcs;
+ USHORT checksum;
tTcpIpPacketParsingResult res = known;
TCPHeader *pTcpHeader = (TCPHeader *)RtlOffsetToPointer(pIpHeader, res.ipHeaderSize);
USHORT saved = pTcpHeader->tcp_xsum;
@@ -395,16 +396,21 @@ VerifyTcpChecksum( IPHeader *pIpHeader, ULONG len, tTcpIpPacketParsingResult kno
else if (res.xxpFull)
{
//USHORT ipFullLength = swap_short(pIpHeader->v4.ip_length);
- pTcpHeader->tcp_xsum = phcs;
- CalculateTcpChecksumGivenPseudoCS(pTcpHeader, xxpHeaderAndPayloadLen);
- if (saved == pTcpHeader->tcp_xsum)
- res.xxpCheckSum = ppresCSOK;
-
if (!(whatToFix & pcrFixXxpChecksum))
- pTcpHeader->tcp_xsum = saved;
+ {
+ checksum = CheckSumCalculator(phcs, pTcpHeader, xxpHeaderAndPayloadLen);
+ if (checksum == 0)
+ res.xxpCheckSum = ppresCSOK;
+ }
else
+ {
+ pTcpHeader->tcp_xsum = phcs;
+ CalculateTcpChecksumGivenPseudoCS(pTcpHeader, xxpHeaderAndPayloadLen);
+ if (saved == pTcpHeader->tcp_xsum)
+ res.xxpCheckSum = ppresCSOK;
res.fixedXxpCS =
res.xxpCheckSum == ppresCSBad || res.xxpCheckSum == ppresPCSOK;
+ }
}
else if (whatToFix)
{
@@ -416,10 +422,9 @@ VerifyTcpChecksum( IPHeader *pIpHeader, ULONG len, tTcpIpPacketParsingResult kno
// we have correct PHCS and we do not need to fix anything
// there is a very small chance that it is also good TCP CS
// in such rare case we give a priority to TCP CS
- CalculateTcpChecksumGivenPseudoCS(pTcpHeader, xxpHeaderAndPayloadLen);
- if (saved == pTcpHeader->tcp_xsum)
+ checksum = CheckSumCalculator(phcs, pTcpHeader, xxpHeaderAndPayloadLen);
+ if (checksum == 0)
res.xxpCheckSum = ppresCSOK;
- pTcpHeader->tcp_xsum = saved;
}
}
else
@@ -437,6 +442,7 @@ static __inline tTcpIpPacketParsingResult
VerifyUdpChecksum( IPHeader *pIpHeader, ULONG len, tTcpIpPacketParsingResult known, ULONG whatToFix)
{
USHORT phcs;
+ USHORT checksum;
tTcpIpPacketParsingResult res = known;
UDPHeader *pUdpHeader = (UDPHeader *)RtlOffsetToPointer(pIpHeader, res.ipHeaderSize);
USHORT saved = pUdpHeader->udp_xsum;
@@ -459,16 +465,21 @@ VerifyUdpChecksum( IPHeader *pIpHeader, ULONG len, tTcpIpPacketParsingResult kno
{
if (res.xxpFull)
{
- pUdpHeader->udp_xsum = phcs;
- CalculateUdpChecksumGivenPseudoCS(pUdpHeader, xxpHeaderAndPayloadLen);
- if (saved == pUdpHeader->udp_xsum)
- res.xxpCheckSum = ppresCSOK;
-
if (!(whatToFix & pcrFixXxpChecksum))
- pUdpHeader->udp_xsum = saved;
+ {
+ checksum = CheckSumCalculator(phcs, pUdpHeader, xxpHeaderAndPayloadLen);
+ if (checksum == 0)
+ res.xxpCheckSum = ppresCSOK;
+ }
else
+ {
+ pUdpHeader->udp_xsum = phcs;
+ CalculateUdpChecksumGivenPseudoCS(pUdpHeader, xxpHeaderAndPayloadLen);
+ if (saved == pUdpHeader->udp_xsum)
+ res.xxpCheckSum = ppresCSOK;
res.fixedXxpCS =
res.xxpCheckSum == ppresCSBad || res.xxpCheckSum == ppresPCSOK;
+ }
}
else
res.xxpCheckSum = ppresXxpIncomplete;
@@ -478,10 +489,9 @@ VerifyUdpChecksum( IPHeader *pIpHeader, ULONG len, tTcpIpPacketParsingResult kno
// we have correct PHCS and we do not need to fix anything
// there is a very small chance that it is also good UDP CS
// in such rare case we give a priority to UDP CS
- CalculateUdpChecksumGivenPseudoCS(pUdpHeader, xxpHeaderAndPayloadLen);
- if (saved == pUdpHeader->udp_xsum)
+ checksum = CheckSumCalculator(phcs, pUdpHeader, xxpHeaderAndPayloadLen);
+ if (checksum == 0)
res.xxpCheckSum = ppresCSOK;
- pUdpHeader->udp_xsum = saved;
}
}
else
--
1.7.7.1.msysgit.0
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