NFS mounts fail after kernel update

This document (000021542) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15 SP5

Situation

On a system which normally performs NFS mounts, after updating the Linux kernel to to 5.14.21-150500.55.59 or to 5.14.21-150500.55.62, the NFS mounts fail. In some cases, while attempting the perform the mounts, the system might reboot.

With this particular type of failure, /var/log/messages will contain the following messages:

kernel: [   49.381985][ T3093] BUG: kernel NULL pointer dereference, address: 0000000000000004

kernel: [   49.382124][ T3093] RIP: 0010:gss_get_mic_kerberos+0x2d/0x300 [rpcsec_gss_krb5]

kernel: [   49.382389][ T3093] Call Trace:
kernel: [   49.382402][ T3093]  <TASK>
kernel: [   49.382426][ T3093]  gss_marshal+0x181/0x320 [auth_rpcgss

Resolution

Update the SLES 15 SP5 kernel to 5.14.21-150500.55.68 or higher.

If a kernel update cannot immediately be performed, and if the NFS client mounts have not been configured to depend on kerberos security, it might be adequate to stop and mask the gss (generic security services) which NFS uses to attempt the detection and use of kerberos:

systemctl stop rpc-gssd
systemctl mask rpc-gssd
systemctl stop rpc-svcgssd
systemctl mask rpc-svcgssd

The above will stop the gss services and also mask (or prevent) them from loading during boot. A "mask" directive can be reversed with an "unmask" directive.

Cause

A memory leak was introduced within some changes made in the RPC GSS code in certain 15 SP5 kernels.

The problem occurs during attempts to use kerberos security with NFS. However, an NFS client system might test the ability to use kerberos (even if not explicitly configured to do so) if it finds kerberos technology configured or active for other reasons. Therefore, this problem can occur during attempts to mount either kerberos or non-kerberos NFS file systems.

Disclaimer

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