[Bug 1926299] [NEW] incorrect sensor is read on Lenovo server BMC

Fri May 21 04:28:20 UTC 2021

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[impact]

ipmi-sensors reads the wrong sensor on a Lenovo BMC (although the
problem may happen on other BMCs as well)

[test case]

run ipmi-sensors over the network using ipmi 1.5 or 2 protocol, and
check the sensor output. Specifically for this case, the server is a
Lenovo SR665 with only 1 cpu socket populated, and dimms 1-16 are
connected to cpu 1 while dimms 17-32 are connected to cpu2, so dimms
17-32 should not return any values.

$ ipmi-sensors -u $USERNAME -p $PASSWD -D LAN_2_0 -l USER -h $BMCADDR | grep DIMM | grep Temp
110 | DIMM 1 Temp | Temperature | N/A | C | N/A
113 | DIMM 2 Temp | Temperature | N/A | C | N/A
116 | DIMM 3 Temp | Temperature | N/A | C | N/A
119 | DIMM 4 Temp | Temperature | N/A | C | N/A
122 | DIMM 5 Temp | Temperature | N/A | C | N/A
125 | DIMM 6 Temp | Temperature | N/A | C | N/A
128 | DIMM 7 Temp | Temperature | N/A | C | N/A
131 | DIMM 8 Temp | Temperature | N/A | C | N/A
134 | DIMM 9 Temp | Temperature | 52.00 | C | 'OK'
137 | DIMM 10 Temp | Temperature | 42.00 | C | 'OK'
140 | DIMM 11 Temp | Temperature | N/A | C | N/A
143 | DIMM 12 Temp | Temperature | N/A | C | N/A
146 | DIMM 13 Temp | Temperature | 27.00 | C | 'OK'
149 | DIMM 14 Temp | Temperature | 26.00 | C | 'OK'
152 | DIMM 15 Temp | Temperature | 24.00 | C | 'OK'
155 | DIMM 16 Temp | Temperature | 24.00 | C | 'OK'
158 | DIMM 17 Temp | Temperature | 218.00 | C | 'OK'
161 | DIMM 18 Temp | Temperature | 212.00 | C | 'OK'
165 | DIMM 19 Temp | Temperature | 212.00 | C | 'OK'
173 | DIMM 20 Temp | Temperature | N/A | C | N/A
176 | DIMM 21 Temp | Temperature | N/A | C | N/A
179 | DIMM 22 Temp | Temperature | N/A | C | N/A
182 | DIMM 23 Temp | Temperature | N/A | C | N/A
185 | DIMM 24 Temp | Temperature | N/A | C | N/A
188 | DIMM 25 Temp | Temperature | 0.00 | C | 'At or Below (<=) Lower Non-Critical Threshold'
191 | DIMM 26 Temp | Temperature | 0.00 | C | 'At or Below (<=) Lower Non-Critical Threshold'
194 | DIMM 27 Temp | Temperature | 0.00 | C | 'At or Below (<=) Lower Non-Critical Threshold'
197 | DIMM 28 Temp | Temperature | 0.00 | C | 'At or Below (<=) Lower Non-Critical Threshold'
200 | DIMM 29 Temp | Temperature | 0.00 | C | 'At or Below (<=) Lower Non-Critical Threshold'
203 | DIMM 30 Temp | Temperature | 0.00 | C | 'At or Below (<=) Lower Non-Critical Threshold'
206 | DIMM 31 Temp | Temperature | 0.00 | C | 'At or Below (<=) Lower Non-Critical Threshold'
209 | DIMM 32 Temp | Temperature | N/A | C | N/A

[regression potential]

any regression would likely result in incorrect values shown for
some/all sensor readings

[scope]

this is not fixed upstream, so it needed in all releases

[other info]

the problem is that this particular BMC has chosen to use a non-zero
'LUN' number for these sensors; almost all BMCs use the standard LUN
number 0, as the spec does state in section 19.3:

"Unless otherwise specified, commands that are listed as mandatory must
be accessed via LUN 00b"

However the spec does allow for implementations to use alternate LUN
numbers, specifically section 5.4 describes how the BMC would report the
LUN number to the requesting software, and section 7.2 clarifies that
while LUN 00b is reserved for devices beloning to the BMC itself and 10b
is reserved for SMS messages, LUN numbers 01b and 11b are reserved for
'OEM' use. So it does appear valid for the BMC implementation to place
sensor(s) under LUN 01b instead of the default 00b.

The cause of the invalid sensor readings in this particular case is
because the BMC also defines sensors with the exact same sensor id
number, but with LUN 00b. So when freeipmi attempts to read e.g. 'DIMM
17 Temp' sensor, it actually reads the current value for a completely
different sensor, which (in this case) isn't even a temperature sensor,
resulting in invalid temperature reading shown for the sensor, instead
of showing it as N/A (since the DIMM slot isn't populated).

Note that ipmitool correctly uses the alternate LUN number so this bug
does not exist with that tool, this affects only freeipmi tooling.

** Affects: freeipmi (Ubuntu)
     Importance: Undecided
     Assignee: Heather Lemon (hypothetical-lemon)
         Status: New

** Affects: freeipmi (Ubuntu Bionic)
     Importance: Low
     Assignee: Heather Lemon (hypothetical-lemon)
         Status: In Progress

** Affects: freeipmi (Ubuntu Focal)
     Importance: Low
     Assignee: Heather Lemon (hypothetical-lemon)
         Status: In Progress

** Affects: freeipmi (Ubuntu Groovy)
     Importance: Low
     Assignee: Heather Lemon (hypothetical-lemon)
         Status: In Progress

** Affects: freeipmi (Ubuntu Hirsute)
     Importance: Low
     Assignee: Heather Lemon (hypothetical-lemon)
         Status: In Progress

** Affects: freeipmi (Ubuntu Impish)
     Importance: Undecided
     Assignee: Heather Lemon (hypothetical-lemon)
         Status: New

** Tags: patch
-- 
incorrect sensor is read on Lenovo server BMC
https://bugs.launchpad.net/bugs/1926299
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