setcap does not recognize CAP_PERFMON

[Nagle-animats]

Ubuntu 20.04 LTS, updated to July 3, 2021.

"setcap" command does not recognize the capability "CAP_PERFMON", in either upper or lower case.
It recognizes other named capabilities.

The same bug has been reported, and fixed, for RedHat/CentOS:

https://bugzilla.redhat.com/show_bug.cgi?id=1946982

[Nagle-animats (nagle-animats)]

Reproduce by:

echo foo > foo
sudo setcap cap_perfmon+ep foo

Result: "Fatal error: Invalid argument"

sudo setcap cap_net_raw_ep foo

Result: blank (success)

getcap foo
foo = cap_net_raw+ep

So cap_net_raw works, but cap_perfmon is not implemented.

[Ubuntu Foundations Team Bug Bot (crichton)]

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[Nagle-animats (nagle-animats)]

setcap belongs to the "libcap" package, per "man setcap"

[Nagle-animats (nagle-animats)]

Reportedly fixed in 21.xx, but broken in 20.04 LTS.

[Adam Dorsey (adorsey)]

Still broken in 20.04 LTS. Unsure if this is related, but the capabilities man page also does not list CAP_PERFMON. Can the fix from newer versions be backported?

[Andrew G. Morgan (morganlibcap)]

Modern kernels include:

 CAP_PERFMON = 38 (supported in upstream libcap-2.36)
 CAP_BPF = 39 (supported in upstream libcap-2.37)
 CAP_CHECKPOINT_RESTORE = 40 (supported in upstream libcap-2.43)

If your kernel supports the capability, but your build of libcap does not, you can work around this by specifying the numerical value of the capability instead. For example:

 sudo setcap cap_perfmon+ep foo

can be worked around as:

 sudo setcap 38=ep foo

At time of writing, upstream libcap is at version 2.66.