[PATCH 2/6] selftests/mm: Fix assumption that sudo is present

[Brendan Jackman <jackmanb@google.com>]

If we are root, sudo isn't needed. If we are not root, we need sudo, so
skip the test if it isn't present.

We already do this for on-fault-limit, but this uses separate
infrastructure since that is specifically for sudo-ing to the nobody
user.

Note this ptrace_skip configuration still fails if that file doesn't
exist, but in that case the test is still fine, so this just prints an
error but doesn't break anything. I suspect that's probably deliberate.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 tools/testing/selftests/mm/run_vmtests.sh | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index da7e266681031d2772fb0c4139648904a18e0bf9..9c963f50927ab2b10c3f942cedd087087d4d0def 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -89,6 +89,17 @@ RUN_ALL=false
 RUN_DESTRUCTIVE=false
 TAP_PREFIX="# "
 
+# We can do stuff as root either if we are already root, or if sudo exists.
+if [ "$(id -u)" == 0 ]; then
+	HAVE_SUDO_ROOT=true
+	SUDO_ROOT=
+elif command -v sudo >/dev/null 2>&1; then
+	HAVE_SUDO_ROOT=true
+	SUDO_ROOT=sudo
+else
+	HAVE_SUDO_ROOT=false
+fi
+
 while getopts "aht:n" OPT; do
 	case ${OPT} in
 		"a") RUN_ALL=true ;;
@@ -384,10 +395,13 @@ CATEGORY="madv_guard" run_test ./guard-pages
 # MADV_POPULATE_READ and MADV_POPULATE_WRITE tests
 CATEGORY="madv_populate" run_test ./madv_populate
 
-if [ -x ./memfd_secret ]
-then
-(echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope 2>&1) | tap_prefix
-CATEGORY="memfd_secret" run_test ./memfd_secret
+if [ -x ./memfd_secret ]; then
+	if $HAVE_SUDO_ROOT; then
+		(echo 0 | $SUDO_ROOT tee /proc/sys/kernel/yama/ptrace_scope 2>&1) | tap_prefix
+		CATEGORY="memfd_secret" run_test ./memfd_secret
+	else
+		echo "# SKIP ./memfd_secret"
+	fi
 fi
 
 # KSM KSM_MERGE_TIME_HUGE_PAGES test with size of 100

-- 
2.48.1.601.g30ceb7b040-goog