From 0f96f02f46d8d72603535c9e1481f245c0ebe2e7 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Marek=20K=C3=BCthe?= <m.k@mk16.de>
Date: Sat, 15 Feb 2025 22:21:13 +0000
Subject: [PATCH] Fix https://github.com/traviscross/mtr/issues/475

With an input of `-28` the expression `(-ctl->cpacketsize - MINPACKET)` became 0, which triggered a zero division. This error is fixed by introducing a check to see if there is any room for randomness. Furthermore, a check of the input arguments in the command line and in curses is performed.
---
 ui/curses.c | 5 ++++-
 ui/mtr.c    | 3 +++
 ui/net.c    | 9 +++++++--
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/ui/curses.c b/ui/curses.c
index 1c41c46..7fc201d 100644
--- a/ui/curses.c
+++ b/ui/curses.c
@@ -202,7 +202,10 @@ int mtr_curses_keyaction(
             buf[i++] = c;       /* need more checking on 'c' */
         }
         buf[i] = '\0';
-        ctl->cpacketsize = atoi(buf);
+        int new_packetsize = atoi(buf);
+        if (abs(ctl->cpacketsize) >= MINPACKET && abs(ctl->cpacketsize) < MAXPACKET) {
+            ctl->cpacketsize = new_packetsize;
+        }
         return ActionNone;
     case 'b':
         mvprintw(2, 0, "Ping Bit Pattern: %d\n", ctl->bitpattern);
diff --git a/ui/mtr.c b/ui/mtr.c
index 447eced..8141771 100644
--- a/ui/mtr.c
+++ b/ui/mtr.c
@@ -452,6 +452,9 @@ static void parse_arg(
         case 's':
             ctl->cpacketsize =
                 strtoint_or_err(optarg, "invalid argument");
+            if (abs(ctl->cpacketsize) < MINPACKET || abs(ctl->cpacketsize) > MAXPACKET) {
+                error(EXIT_FAILURE, 0, "value of of range (%d - %d)", MINPACKET, MAXPACKET);
+            }
             break;
         case 'I':
             ctl->InterfaceName = optarg;
diff --git a/ui/net.c b/ui/net.c
index 45c33ec..4df7b74 100644
--- a/ui/net.c
+++ b/ui/net.c
@@ -561,8 +561,13 @@ int net_send_batch(
                smaller (reasonable packet sizes), and our rand() range much
                larger, this effect is insignificant. Oh! That other formula
                didn't work. */
-            packetsize =
-                MINPACKET + rand() % (-ctl->cpacketsize - MINPACKET);
+            if (-ctl->cpacketsize <= MINPACKET) {
+                /* There is no room to introduce randomness. */
+                packetsize = MINPACKET;
+            } else {
+                packetsize =
+                    MINPACKET + rand() % (-ctl->cpacketsize - MINPACKET);
+            }
         } else {
             packetsize = ctl->cpacketsize;
         }
-- 
2.47.2