[OpenAFS] Windows client and firewall/antivirus/MTU conflict - possibility of file corruption

[Jeffrey Altman]

This is a cryptographically signed message in MIME format.

--------------ms030401040207040103090802
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

What follows is an update on this issue.

The Problem:

Symantec Endpoint Protection 11.0.4 (Network Threat Protection)
periodically corrupts outbound UDP packets that are subject to
fragmentation.  In addition, any version of SEP 11.0.x including
11.0.5 results in performance degradation when UDP packets are
fragmented.


Why does data corruption not affect OpenAFS/Win 1.5.33 and earlier?

All versions of OpenAFS for Windows 1.3.50 to 1.5.33 included
by default a cap on the MTU size used for sending and receiving
packets within the Rx library.  This cap was configured using the
TransarcAFSDaemon\Parameters "RxMaxMTU" value.  A value of 1260
was used to permit OpenAFS communications to work in conjunction
with Cisco IPSec VPN 4.x clients.


Why does data corruption affect OpenAFS/Win 1.5.34 through 1.5.68?

Cisco VPN Client 5.0 fixed the problems with OpenAFS.  By the time
1.5.34 was released, 5.0 had been out for a significant period of
time and was widely distributed within the OpenAFS community.
It was determined that the >10% performance hit caused by not
sending full UDP packets was no longer required by the default
installation.


If the Windows network interface MTU is set to 1300, why does
OpenAFS continue to use 1444?

OpenAFS for Windows uses the IP Helper Library GetAdapterAddresses()
function to obtain the configuration data for all of the
installed network interfaces.  This API fails to report the
static MTU limit restriction if one is configured in the registry.
As a result, OpenAFS for Windows is unaware that the network
interface will fragment UDP packets larger than the assigned value.


How is this problem being addressed in 1.5.69?

Asanka Herath (Secure Endpoints) contributed a patch to search
for a registry assigned MTU value for each network interface which
permits OpenAFS for Windows to report the correct MTU values to
the Rx library and in response to the "cmdebug <host> -addrs"
query.  http://gerrit.openafs.org/#change,1105

In addition, a patch to the Rx library ensures that the interface
MTU values are used to limit packet size on sends as well as
on receives.  http://gerrit.openafs.org/#change,1107

When these two patches are applied, packet fragmentation will
not occur.  As a result the performance degradation and data
corruption caused by Symantec Endpoint Protection will be avoided.


Acknowledgments

Thanks to Richard Brittain and his management at Dartmouth for
the significant quantity of his time that was dedicated over the last
two months to help narrow down the root cause of this problem.  Without
their efforts, the gatekeepers could not have resolved this issue on
behalf of the community.

Jeffrey Altman








--------------ms030401040207040103090802
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
Content-Description: S/MIME Cryptographic Signature

MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIJeTCC
AxcwggKAoAMCAQICEAMF9RTCGOz151fTpHLih+cwDQYJKoZIhvcNAQEFBQAwYjELMAkGA1UE
BhMCWkExJTAjBgNVBAoTHFRoYXd0ZSBDb25zdWx0aW5nIChQdHkpIEx0ZC4xLDAqBgNVBAMT
I1RoYXd0ZSBQZXJzb25hbCBGcmVlbWFpbCBJc3N1aW5nIENBMB4XDTA5MDgyODA0MDExOVoX
DTEwMDgyODA0MDExOVowczEPMA0GA1UEBBMGQWx0bWFuMRUwEwYDVQQqEwxKZWZmcmV5IEVy
aWMxHDAaBgNVBAMTE0plZmZyZXkgRXJpYyBBbHRtYW4xKzApBgkqhkiG9w0BCQEWHGphbHRt
YW5Ac2VjdXJlLWVuZHBvaW50cy5jb20wggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIB
AQDZNscYIvF6xzGSAfa/QUIqiElyn0EUxL2b86eKiYqe91bj0gLr/MJoErLnb+OmokxqSAH6
y0zlFqSbiFwgNM8m69K6m/6YO+x3+5zBc+u6snwTWMEWygnhx3rQ/lMhoQOgArraL+/k9aWL
kNdaXQKk6EZVW9pfV2A4Lk4DoZGFjY8tJRWWDLlFkYnxDuIEpLYwJpwakv3QHOaq/G8KW0iE
jVhVzPobuZzwD2tuepY/bsClwqxz/gfAEpUvAn/lYTqnoT7RYljZlCIdbrgcG/HSYMxAy1Zp
Yh8Fx+9cqsG8O4nqo26SVfYZvrYhh8m6OqW8Vakdt7vBLCTa/QhIdJ4hAgMBAAGjOTA3MCcG
A1UdEQQgMB6BHGphbHRtYW5Ac2VjdXJlLWVuZHBvaW50cy5jb20wDAYDVR0TAQH/BAIwADAN
BgkqhkiG9w0BAQUFAAOBgQBvbvJNXUJ4atv1CExIe0J38jZqoEUTttkXOfCDT9e3mSmVboOK
ifHDyLZQC4qSsCUfP7vdwAXjKtjak22HbfX2sEKCUgtnOkxRqXMM2V/NW/ESNVQZF0TO7L/Z
cW3icObO9FIZCSmgFMt2Al7VPfMQmaJNlqu9SLmXSwbRFJ5b4zCCAxcwggKAoAMCAQICEAMF
9RTCGOz151fTpHLih+cwDQYJKoZIhvcNAQEFBQAwYjELMAkGA1UEBhMCWkExJTAjBgNVBAoT
HFRoYXd0ZSBDb25zdWx0aW5nIChQdHkpIEx0ZC4xLDAqBgNVBAMTI1RoYXd0ZSBQZXJzb25h
bCBGcmVlbWFpbCBJc3N1aW5nIENBMB4XDTA5MDgyODA0MDExOVoXDTEwMDgyODA0MDExOVow
czEPMA0GA1UEBBMGQWx0bWFuMRUwEwYDVQQqEwxKZWZmcmV5IEVyaWMxHDAaBgNVBAMTE0pl
ZmZyZXkgRXJpYyBBbHRtYW4xKzApBgkqhkiG9w0BCQEWHGphbHRtYW5Ac2VjdXJlLWVuZHBv
aW50cy5jb20wggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQDZNscYIvF6xzGSAfa/
QUIqiElyn0EUxL2b86eKiYqe91bj0gLr/MJoErLnb+OmokxqSAH6y0zlFqSbiFwgNM8m69K6
m/6YO+x3+5zBc+u6snwTWMEWygnhx3rQ/lMhoQOgArraL+/k9aWLkNdaXQKk6EZVW9pfV2A4
Lk4DoZGFjY8tJRWWDLlFkYnxDuIEpLYwJpwakv3QHOaq/G8KW0iEjVhVzPobuZzwD2tuepY/
bsClwqxz/gfAEpUvAn/lYTqnoT7RYljZlCIdbrgcG/HSYMxAy1ZpYh8Fx+9cqsG8O4nqo26S
VfYZvrYhh8m6OqW8Vakdt7vBLCTa/QhIdJ4hAgMBAAGjOTA3MCcGA1UdEQQgMB6BHGphbHRt
YW5Ac2VjdXJlLWVuZHBvaW50cy5jb20wDAYDVR0TAQH/BAIwADANBgkqhkiG9w0BAQUFAAOB
gQBvbvJNXUJ4atv1CExIe0J38jZqoEUTttkXOfCDT9e3mSmVboOKifHDyLZQC4qSsCUfP7vd
wAXjKtjak22HbfX2sEKCUgtnOkxRqXMM2V/NW/ESNVQZF0TO7L/ZcW3icObO9FIZCSmgFMt2
Al7VPfMQmaJNlqu9SLmXSwbRFJ5b4zCCAz8wggKooAMCAQICAQ0wDQYJKoZIhvcNAQEFBQAw
gdExCzAJBgNVBAYTAlpBMRUwEwYDVQQIEwxXZXN0ZXJuIENhcGUxEjAQBgNVBAcTCUNhcGUg
VG93bjEaMBgGA1UEChMRVGhhd3RlIENvbnN1bHRpbmcxKDAmBgNVBAsTH0NlcnRpZmljYXRp
b24gU2VydmljZXMgRGl2aXNpb24xJDAiBgNVBAMTG1RoYXd0ZSBQZXJzb25hbCBGcmVlbWFp
bCBDQTErMCkGCSqGSIb3DQEJARYccGVyc29uYWwtZnJlZW1haWxAdGhhd3RlLmNvbTAeFw0w
MzA3MTcwMDAwMDBaFw0xMzA3MTYyMzU5NTlaMGIxCzAJBgNVBAYTAlpBMSUwIwYDVQQKExxU
aGF3dGUgQ29uc3VsdGluZyAoUHR5KSBMdGQuMSwwKgYDVQQDEyNUaGF3dGUgUGVyc29uYWwg
RnJlZW1haWwgSXNzdWluZyBDQTCBnzANBgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEAxKY8VXNV
+065yplaHmjAdQRwnd/p/6Me7L3N9VvyGna9fww6YfK/Uc4B1OVQCjDXAmNaLIkVcI7dyfAr
hVqqP3FWy688Cwfn8R+RNiQqE88r1fOCdz0Dviv+uxg+B79AgAJk16emu59l0cUqVIUPSAR/
p7bRPGEEQB5kGXJgt/sCAwEAAaOBlDCBkTASBgNVHRMBAf8ECDAGAQH/AgEAMEMGA1UdHwQ8
MDowOKA2oDSGMmh0dHA6Ly9jcmwudGhhd3RlLmNvbS9UaGF3dGVQZXJzb25hbEZyZWVtYWls
Q0EuY3JsMAsGA1UdDwQEAwIBBjApBgNVHREEIjAgpB4wHDEaMBgGA1UEAxMRUHJpdmF0ZUxh
YmVsMi0xMzgwDQYJKoZIhvcNAQEFBQADgYEASIzRUIPqCy7MDaNmrGcPf6+svsIXoUOWlJ1/
TCG4+DYfqi2fNi/A9BxQIJNwPP2t4WFiw9k6GX6EsZkbAMUaC4J0niVQlGLH2ydxVyWN3amc
OY6MIE9lX5Xa9/eH1sYITq726jTlEBpbNU1341YheILcIRk13iSx0x1G/11fZU8xggNxMIID
bQIBATB2MGIxCzAJBgNVBAYTAlpBMSUwIwYDVQQKExxUaGF3dGUgQ29uc3VsdGluZyAoUHR5
KSBMdGQuMSwwKgYDVQQDEyNUaGF3dGUgUGVyc29uYWwgRnJlZW1haWwgSXNzdWluZyBDQQIQ
AwX1FMIY7PXnV9OkcuKH5zAJBgUrDgMCGgUAoIIB0DAYBgkqhkiG9w0BCQMxCwYJKoZIhvcN
AQcBMBwGCSqGSIb3DQEJBTEPFw0xMDAxMTUxNzMzNTVaMCMGCSqGSIb3DQEJBDEWBBQQRnWc
BwI8wtKsorR6JSFL9sJzKDBfBgkqhkiG9w0BCQ8xUjBQMAsGCWCGSAFlAwQBAjAKBggqhkiG
9w0DBzAOBggqhkiG9w0DAgICAIAwDQYIKoZIhvcNAwICAUAwBwYFKw4DAgcwDQYIKoZIhvcN
AwICASgwgYUGCSsGAQQBgjcQBDF4MHYwYjELMAkGA1UEBhMCWkExJTAjBgNVBAoTHFRoYXd0
ZSBDb25zdWx0aW5nIChQdHkpIEx0ZC4xLDAqBgNVBAMTI1RoYXd0ZSBQZXJzb25hbCBGcmVl
bWFpbCBJc3N1aW5nIENBAhADBfUUwhjs9edX06Ry4ofnMIGHBgsqhkiG9w0BCRACCzF4oHYw
YjELMAkGA1UEBhMCWkExJTAjBgNVBAoTHFRoYXd0ZSBDb25zdWx0aW5nIChQdHkpIEx0ZC4x
LDAqBgNVBAMTI1RoYXd0ZSBQZXJzb25hbCBGcmVlbWFpbCBJc3N1aW5nIENBAhADBfUUwhjs
9edX06Ry4ofnMA0GCSqGSIb3DQEBAQUABIIBALPbgzA/x2PuzO1ou8khRLmVyoG8ds2cdmog
NSnE3hXtX+0OoyIaZIMwJaDKxAsRIWNQTUvMayIu+lMpWHgEy/n92rfhKnw6cSlssxOgrncR
dohvIAKbwMCVAhPioSCgON9uP7vgcuBAFN7/fDMkRK22GYkvAoWteDNuLvCNDh9RUjfGa+Bf
NYVulzFnsAwrCB7LSOaSOfXkTYDIDEknG5wsoGfiVUMXsQx3qHUPuRWsxAT1xPY8qHWZ6m7D
fhk7lvJAsBKnmG6YkRPUgmoXmIRmdj90LTxr7X1VK4YFWN1lctS5BFkH8OoHxFxgc6YpWHpr
jDAiC5mVYoSxaidvBBcAAAAAAAA=
--------------ms030401040207040103090802--