selftests/lkdtm: Reset WARN_ONCE to avoid false negatives

Since we expect to see warnings every time for many tests, just reset
the WARN_ONCE flags each time the script runs.

Fixes: 46d1a0f0 ("selftests/lkdtm: Add tests for LKDTM targets")
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200625203704.317097-4-keescook@chromium.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/testing/selftests/lkdtm/run.sh

@@ -8,6 +8,7 @@
 #
 set -e
 TRIGGER=/sys/kernel/debug/provoke-crash/DIRECT
+CLEAR_ONCE=/sys/kernel/debug/clear_warn_once
 KSELFTEST_SKIP_TEST=4
 
 # Verify we have LKDTM available in the kernel.
@@ -67,6 +68,11 @@ cleanup() {
 }
 trap cleanup EXIT
 
+# Reset WARN_ONCE counters so we trip it each time this runs.
+if [ -w $CLEAR_ONCE ] ; then
+	echo 1 > $CLEAR_ONCE
+fi
+
 # Save existing dmesg so we can detect new content below
 dmesg > "$DMESG"