From fcfe01f301c52b7916f4b5e4ba570f7461e959cc Mon Sep 17 00:00:00 2001
From: Tomas Babej <tomas@tbabej.com>
Date: Sun, 6 Dec 2020 20:49:35 -0500
Subject: [PATCH] recur: Prevent infinite loops with 0 periods

Specifying a recurrence interval that amounts to a zero, like 'P0M', 0q
or 0m causes task to fall into an infinite loop when trying to determine
next recurrence dates.

Detect scenarios with zero-length recurrence interval and throw an
exception.

Closes #2262.
---
 src/recur.cpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/recur.cpp b/src/recur.cpp
index c14539c99..8a0353cc7 100644
--- a/src/recur.cpp
+++ b/src/recur.cpp
@@ -234,6 +234,9 @@ Datetime getNextRecurrence (Datetime& current, std::string& period)
   {
     int increment = strtol (period.substr (0, period.length () - 1).c_str (), nullptr, 10);
 
+    if (increment <= 0)
+      throw format ("Recurrence period '{1}' is equivalent to {2} and hence invalid.", period, increment);
+
     m += increment;
     while (m > 12)
     {
@@ -253,6 +256,9 @@ Datetime getNextRecurrence (Datetime& current, std::string& period)
   {
     int increment = strtol (period.substr (1, period.length () - 2).c_str (), nullptr, 10);
 
+    if (increment <= 0)
+      throw format ("Recurrence period '{1}' is equivalent to {2} and hence invalid.", period, increment);
+
     m += increment;
     while (m > 12)
     {
@@ -286,6 +292,9 @@ Datetime getNextRecurrence (Datetime& current, std::string& period)
   {
     int increment = strtol (period.substr (0, period.length () - 1).c_str (), nullptr, 10);
 
+    if (increment <= 0)
+      throw format ("Recurrence period '{1}' is equivalent to {2} and hence invalid.", period, increment);
+
     m += 3 * increment;
     while (m > 12)
     {