Add support for random values using the '~' operator.

For example "0~30" will result in a random value between 0 and 30
inclusive.  If either (or both) of the numbers on either side of
the '~' are omitted, the appropriate limit (low or high) for the
field will be used.  OK deraadt@ beck@ jmc@

2 files changed, 65 insertions, 20 deletions

diff --git a/usr.sbin/cron/crontab.5 b/usr.sbin/cron/crontab.5
index f9b4446cf87..ef9ac0a6672 100644
--- a/usr.sbin/cron/crontab.5
+++ b/usr.sbin/cron/crontab.5
@@ -17,9 +17,9 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
 .\" OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.\" $OpenBSD: crontab.5,v 1.37 2020/01/06 19:44:09 job Exp $
+.\" $OpenBSD: crontab.5,v 1.38 2020/04/15 01:59:34 millert Exp $
 .\"
-.Dd $Mdocdate: January 6 2020 $
+.Dd $Mdocdate: April 15 2020 $
 .Dt CRONTAB 5
 .Os
 .Sh NAME
@@ -144,7 +144,18 @@ For example,
 .Ar hour
 entry specifies execution at hours 8, 9, 10 and 11.
 .Pp
-Step values can be used in conjunction with ranges.
+A random value (within the legal range) may be obtained by using the
+.Ql ~
+character in a field.
+The interval of the random value may be specified explicitly, for example
+.Dq 0~30
+will result in a random value between 0 and 30 inclusive.
+If either (or both) of the numbers on either side of the
+.Ql ~
+are omitted, the appropriate limit (low or high) for the field will be used.
+.Pp
+Step values can be used in conjunction with ranges (but not random ranges
+which represent a single number).
 Following a range with
 .No / Ns Ar number
 specifies skips of
@@ -318,6 +329,9 @@ MAILTO=paul
 23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
 
 5 4 * * sun     echo "run at 5 after 4 every sunday"
+
+# run hourly at a random time within the first 30 minutes of the hour
+0~30 * * * *   /usr/libexec/spamd-setup
 .Ed
 .Sh SEE ALSO
 .Xr crontab 1 ,
@@ -338,6 +352,10 @@ field may use 7 to represent Sunday.
 Ranges may include
 .Dq steps .
 .It
+Random intervals are supported using the
+.Ql ~
+character.
+.It
 Months or days of the week can be specified by name.
 .It
 Mailing after a successful run can be suppressed with
diff --git a/usr.sbin/cron/entry.c b/usr.sbin/cron/entry.c
index bb0221bffb6..e3f919a86e3 100644
--- a/usr.sbin/cron/entry.c
+++ b/usr.sbin/cron/entry.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: entry.c,v 1.49 2018/06/13 11:27:30 job Exp $	*/
+/*	$OpenBSD: entry.c,v 1.50 2020/04/15 01:59:34 millert Exp $	*/
 
 /*
  * Copyright 1988,1990,1993,1994 by Paul Vixie
@@ -450,33 +450,29 @@ static int
 get_range(bitstr_t *bits, int low, int high, const char *names[],
 	  int ch, FILE *file)
 {
-	/* range = number | number "-" number [ "/" number ]
+	/* range = number | number* "~" number* | number "-" number ["/" number]
 	 */
 
 	int i, num1, num2, num3;
 
+	num1 = low;
+	num2 = high;
+
 	if (ch == '*') {
-		/* '*' means "first-last" but can still be modified by /step
+		/* '*' means [low, high] but can still be modified by /step
 		 */
-		num1 = low;
-		num2 = high;
 		ch = get_char(file);
 		if (ch == EOF)
 			return (EOF);
 	} else {
-		ch = get_number(&num1, low, names, ch, file, ",- \t\n");
-		if (ch == EOF)
-			return (EOF);
-
-		if (ch != '-') {
-			/* not a range, it's a single number.
-			 */
-			if (EOF == set_element(bits, low, high, num1)) {
-				unget_char(ch, file);
+		if (ch != '~') {
+			ch = get_number(&num1, low, names, ch, file, ",-~ \t\n");
+			if (ch == EOF)
 				return (EOF);
-			}
-			return (ch);
-		} else {
+		}
+
+		switch (ch) {
+		case '-':
 			/* eat the dash
 			 */
 			ch = get_char(file);
@@ -488,6 +484,37 @@ get_range(bitstr_t *bits, int low, int high, const char *names[],
 			ch = get_number(&num2, low, names, ch, file, "/, \t\n");
 			if (ch == EOF || num1 > num2)
 				return (EOF);
+			break;
+		case '~':
+			/* eat the tilde
+			 */
+			ch = get_char(file);
+			if (ch == EOF)
+				return (EOF);
+
+			/* get the (optional) number following the tilde
+			 */
+			ch = get_number(&num2, low, names, ch, file, ", \t\n");
+			if (ch == EOF)
+				ch = get_char(file);
+			if (ch == EOF || num1 > num2) {
+				unget_char(ch, file);
+				return (EOF);
+			}
+
+			/* get a random number in the interval [num1, num2]
+			 */
+			num3 = num1;
+			num1 = arc4random_uniform(num2 - num3 + 1) + num3;
+			/* FALLTHROUGH */
+		default:
+			/* not a range, it's a single number.
+			 */
+			if (EOF == set_element(bits, low, high, num1)) {
+				unget_char(ch, file);
+				return (EOF);
+			}
+			return (ch);
 		}
 	}