ctdb-tools: Fix CID 1539212 - signed/unsigned issue

>>>     CID 1539212:  Control flow issues  (NO_EFFECT)
>>>     This greater-than-or-equal-to-zero comparison of an unsigned value is always true. "p >= 0UL".
216     		while (p >= 0 && output[p] == '\n') {

This is a real problem in the unlikely event that the output contains
only newlines.

Fix the issue by using a pointer and add a test to cover this case.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15438

Signed-off-by: Martin Schwenke <mschwenke@ddn.com>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>

ctdb/event/event_tool.c

@@ -203,7 +203,6 @@ static void print_status_one(struct ctdb_event_script *script)
 		const char *t = script->output == NULL ? "" : script->output;
 		size_t len = strlen(t);
 		char output[len+1];
-		size_t p;
 		char *t1, *t2;
 
 		strlcpy(output, t, sizeof(output));
@@ -212,10 +211,10 @@ static void print_status_one(struct ctdb_event_script *script)
 		 * Strip trailing newlines, they are clutter and
 		 * interfere with multi-line detection
 		 */
-		p = len - 1;
-		while (p >= 0 && output[p] == '\n') {
-			output[p] = '\0';
-			p--;
+		t1 = output + len - 1;
+		while (t1 >= output && *t1 == '\n') {
+			*t1 = '\0';
+			t1--;
 		}
 
 		/* If the output is a single line then print it inline */

ctdb/tests/UNIT/eventd/etc-ctdb/events/random/02.enabled.script

@@ -24,6 +24,14 @@ EOF
 	printf 'No trailing newline'
 	exit 0
 	;;
+"verbosenewlinesonly")
+	cat <<EOF
+
+
+
+EOF
+	exit 0
+	;;
 "verbosefailure") echo "args: $*"; exit 1 ;;
 "verbosemultilinefailure")
 	cat <<EOF

ctdb/tests/UNIT/eventd/eventd_008.sh

@@ -56,6 +56,16 @@ ok <<EOF
 EOF
 simple_test status random verbosemultilinenonl
 
+ok_null
+simple_test run 10 random verbosenewlinesonly
+
+ok <<EOF
+01.disabled          DISABLED  
+02.enabled           OK         DURATION DATETIME
+  OUTPUT: 
+EOF
+simple_test status random verbosenewlinesonly
+
 required_result 8 <<EOF
 Event verbosemultilinefailure in random failed
 EOF