linux-kernel - Re: [PATCH] selftests/mm: Don't needlessly use sudo to obtain root in run

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Message-ID: <ZcdthfAvzLQ9lzvd@finisterre.sirena.org.uk>
Date: Sat, 10 Feb 2024 12:35:17 +0000
From: Mark Brown <broonie@...nel.org>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Shuah Khan <shuah@...nel.org>, linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/mm: Don't needlessly use sudo to obtain root
 in run_vmtests.sh

On Sat, Feb 10, 2024 at 07:40:16AM +0000, Ryan Roberts wrote:
> On 09/02/2024 20:21, Mark Brown wrote:

> > When opening yama/ptrace_scope we unconditionally use sudo to ensure we
> > are running as root, resulting in failures if running in a minimal root
> > filesystem where sudo is not installed. Since automated test systems will
> > typically just run all of kselftest as root (and many kselftests rely on
> > this for full functionality) add a check to see if we're already root and
> > only invoke sudo if not.

> I don't really see the point of this. run_vmtests.sh needs to be run as root;
> there are lots of operations that depend on it and most tests will fail if not
> root. So I think it would be much cleaner just to remove this instance sudo.

Ah, I was assuming that some of the suite ran usefully as non-root given
that the only point of that sudo was to acquire root.  If the whole
thing needs to be root then we should instead have a check for root at
the top of run_vmtests.sh and just skip the whole thing if we aren't
root, but then I'm unclear why it's invoking sudo in the first place.

> The problem that I was referring to yesterday, about needing sudo was for this case:

> CATEGORY="mlock" run_test sudo -u nobody ./on-fault-limit

> Here, we are using sudo to deprivilege ourselves from root and run
> on-fault-limit as nobody. This is required because the test is checking an
> rlimit that is only enforced for normal users.

> Somebody on list was talking about skipping this test if sudo wasn't present a
> couple of weeks back. Not sure if that happened.

Yes, there's a check:

	if command -v sudo &> /dev/null;
	then
	        CATEGORY="mlock" run_test sudo -u nobody ./on-fault-limit
	else
	        echo "# SKIP ./on-fault-limit"
	fi

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