Github Action Runners creating world-writable shared memory section: lttng-ust-wait-n

[bill robertson]

GHA runners appear to use lttng-ust for some sort of IPC between runners on
the same machine.

$ ll /dev/shm/

-rw-rw-rw- 1 gha-runner-7 gha-runner-7  4096 Feb 20 04:03 lttng-ust-wait-8
-rw-r----- 1 gha-runner-8 gha-runner-8  4096 Feb 20 04:03 lttng-ust-wait-8-558
-rw-r----- 1 gha-runner-7 gha-runner-7  4096 Feb 20 04:03 lttng-ust-wait-8-559
-rw-r----- 1 gha-runner-6 gha-runner-6  4096 Feb 20 04:03 lttng-ust-wait-8-560
-rw-r----- 1 gha-runner-5 gha-runner-5  4096 Feb 20 04:03 lttng-ust-wait-8-561
-rw-r----- 1 gha-runner-4 gha-runner-4  4096 Feb 20 04:03 lttng-ust-wait-8-562
-rw-r----- 1 gha-runner-3 gha-runner-3  4096 Feb 20 04:03 lttng-ust-wait-8-563
-rw-r----- 1 gha-runner-2 gha-runner-2  4096 Feb 20 04:03 lttng-ust-wait-8-564
-rw-r----- 1 gha-runner-1 gha-runner-1  4096 Feb 20 04:03 lttng-ust-wait-8-565


I assume that this is their code, and not some configuration issue on the
host machine, but if this may not be the case, can someone explain what can
be done or point me to information on the subject?

Otherwise, is there some sort of environment variable or other setting that
lttng will reference when creating this shared memory section such that it
is not world-writable? All of the runners run under user accounts that are
in a common group.

Thanks!
Bill
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