bin/53476: crontab: Randomly selected number (question mark) may be negative

[netbsd-bugs%michael-kaufmann.ch@localhost]

>Number:         53476
>Category:       bin
>Synopsis:       crontab: Randomly selected number (question mark) may be negative
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Jul 28 12:10:00 +0000 2018
>Originator:     Michael Kaufmann
>Release:        8.0
>Organization:
>Environment:
NetBSD cubieboard 8.0 NetBSD 8.0 (CUBIEBOARD) #0: Tue Jul 17 14:59:51 UTC 2018  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/evbarm/compile/CUBIEBOARD evbarm
>Description:
A crontab entry may contain a question mark '?', e.g.
? 3 * * * $HOME/task.sh

Sometimes crontab fails when activating such a configuration:
crontab: installing new crontab
"/tmp/crontab.8GkRCbU1KQ":1: bad minute
crontab: errors in crontab file, can't install.

The reason is that sometimes a negative value (out of range) is chosen for the minute.
>How-To-Repeat:
Configure this job with "crontab -e":
? 3 * * * $HOME/task.sh

Repeat this multiple times. It will fail in about half of the tries.
>Fix:
The bug is in the "random_with_range" function:

return (int)arc4random() % (high - low + 1) + low;


Proposed bugfix:

return (int)(arc4random() % (high - low + 1) + low);