snmpwalk hrstorage reports incorrect sizes

SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP3

A "df" report shows certain sizes for /home and other file systems, but snmpwalk hrstorage reports incorrect values.

For example:

 # /bin/df -Th
# (this output has been trimmed)

Filesystem                     Type      Size  Used Avail Use% Mounted on
tmpfs                          tmpfs     362M   38M  325M  11% /run
/dev/mapper/system-root        btrfs     1.0G  480M  354M  58% /
/dev/mapper/system-home        btrfs      43G   34G  9.4G  78% /home

Below, the root file system ("/") reports correctly within snmpwalk output, as the "Size" and "Used" values, when multiplied by the Unit (4096), is the same size as reported in "df".  For example, Size 262144 x 4096 = 1073741824, aka 1 GB:

HOST-RESOURCES-MIB::hrStorageIndex.31 = INTEGER: 31
HOST-RESOURCES-MIB::hrStorageType.31 = OID: HOST-RESOURCES-TYPES::hrStorageFixedDisk
HOST-RESOURCES-MIB::hrStorageDescr.31 = STRING: /
HOST-RESOURCES-MIB::hrStorageAllocationUnits.31 = INTEGER: 4096 Bytes
HOST-RESOURCES-MIB::hrStorageSize.31 = INTEGER: 262144
HOST-RESOURCES-MIB::hrStorageUsed.31 = INTEGER: 122888

However, the /home file system (and possibly others) report incorrect values:

HOST-RESOURCES-MIB::hrStorageIndex.78 = INTEGER: 78
HOST-RESOURCES-MIB::hrStorageType.78 = OID: HOST-RESOURCES-TYPES::hrStorageFixedDisk
HOST-RESOURCES-MIB::hrStorageDescr.78 = STRING: /home
HOST-RESOURCES-MIB::hrStorageAllocationUnits.78 = INTEGER: 4096 Bytes
HOST-RESOURCES-MIB::hrStorageSize.78 = INTEGER: 92575
HOST-RESOURCES-MIB::hrStorageUsed.78 = INTEGER: 9558

If those values are calculated together, the result (for example 92575 x 4096 = 379,187,200 = approx 362 MB) is incorrect for that file system.  Incidentally, that size value actually belongs to the tmpfs file system mounted at /run, instead.
 

If maintenance updates for your SLES distribution provide net-snmp 5.9.3-150300.15.8.1, update to that version (or higher).

Alternatively, the problem can be manually corrected with these steps:

1.  Execute:  systemctl edit snmpd

That will create /etc/systemd/system/snmpd.service.d/override.conf and bring it up in an editor.

2.  Insert into that file:
[Service]
ProtectHome=false

3.  After saving and exiting that file, execute:
systemctl daemon-reload
systemctl restart snmpd

A previous update intended to harden security of snmpd enabled an option called "ProtectHome".  This has the side effect of causing /home (and possibly other file systems) to be classified as a tmpfs and return incorrect results.  The hardening patch has been reworked / replaced, and the new one does not contain that option.

From the changelog of net-snmp 5.9.3-150300.15.8.1 (trimmed):

* Mon Jan 09 2023 
- Hardening systemd services setting "ProtectHome=true" caused home directory
  size and allocation to be listed incorrectly (bsc#1206044).
  add:
  * net-snmp-5.9.3-harden_snmpd.service.patch
  delete:
  * net-snmp-5.9.1-harden_snmpd.service.patch