From 33916513233ce53b340752a33eff6c9c3914d5c9 Mon Sep 17 00:00:00 2001
From: krcroft <krcroft@users.noreply.github.com>
Date: Sat, 18 Jan 2020 15:29:10 -0800
Subject: [PATCH] Fix NULL issues in shell code

---
 src/shell/shell.cpp      |  9 +++++++++
 src/shell/shell_cmds.cpp | 19 ++++++++++++-------
 src/shell/shell_misc.cpp |  8 ++++----
 3 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/src/shell/shell.cpp b/src/shell/shell.cpp
index 7441dc96..3b44fdbf 100644
--- a/src/shell/shell.cpp
+++ b/src/shell/shell.cpp
@@ -202,6 +202,11 @@ Bitu DOS_Shell::GetRedirection(char *s, char **ifn, char **ofn,bool * append) {
 //			else
 //				*lr=0;
 			t = (char*)malloc(lr-*ofn+1);
+			if (t == nullptr) {
+				E_Exit("SHELL: Could not allocate %u bytes in parser",
+				       static_cast<unsigned int>(lr-*ofn+1));
+			}
+
 			safe_strncpy(t,*ofn,lr-*ofn+1);
 			*ofn=t;
 			continue;
@@ -216,6 +221,10 @@ Bitu DOS_Shell::GetRedirection(char *s, char **ifn, char **ofn,bool * append) {
 //			else
 //				*lr=0;
 			t = (char*)malloc(lr-*ifn+1);
+			if (t == nullptr) {
+				E_Exit("SHELL: Could not allocate %u bytes in parser",
+				       static_cast<unsigned int>(lr-*ifn+1));
+			}
 			safe_strncpy(t,*ifn,lr-*ifn+1);
 			*ifn=t;
 			continue;
diff --git a/src/shell/shell_cmds.cpp b/src/shell/shell_cmds.cpp
index 1c8020b6..bed75ad3 100644
--- a/src/shell/shell_cmds.cpp
+++ b/src/shell/shell_cmds.cpp
@@ -1319,20 +1319,25 @@ void DOS_Shell::CMD_CHOICE(char * args){
 	HELP("CHOICE");
 	static char defchoice[3] = {'y','n',0};
 	char *rem = NULL, *ptr;
-	bool optN = ScanCMDBool(args,"N");
-	bool optS = ScanCMDBool(args,"S"); //Case-sensitive matching
-	ScanCMDBool(args,"T"); //Default Choice after timeout
+	bool optN = false;
+	bool optS = false;
 	if (args) {
+		optN = ScanCMDBool(args,"N");
+		optS = ScanCMDBool(args,"S"); //Case-sensitive matching
+		ScanCMDBool(args,"T"); //Default Choice after timeout
 		char *last = strchr(args,0);
 		StripSpaces(args);
 		rem = ScanCMDRemain(args);
+
 		if (rem && *rem && (tolower(rem[1]) != 'c')) {
 			WriteOut(MSG_Get("SHELL_ILLEGAL_SWITCH"),rem);
 			return;
 		}
 		if (args == rem) {
 			assert(args);
-			args = strchr(rem, '\0') + 1;
+			if (rem != nullptr) {
+				args = strchr(rem, '\0') + 1;
+			}
 		}
 		if (rem) rem += 2;
 		if(rem && rem[0]==':') rem++; /* optional : after /c */
@@ -1379,10 +1384,10 @@ void DOS_Shell::CMD_ATTRIB(char *args){
 
 void DOS_Shell::CMD_PATH(char *args){
 	HELP("PATH");
-	if(args && *args && strlen(args)){
+	if(args && strlen(args)){
 		char pathstring[DOS_PATHLENGTH+CROSS_LEN+20]={ 0 };
 		strcpy(pathstring,"set PATH=");
-		while(args && *args && (*args=='='|| *args==' ')) 
+		while(args && *args && (*args=='='|| *args==' '))
 		     args++;
 		strcat(pathstring,args);
 		this->ParseLine(pathstring);
@@ -1398,7 +1403,7 @@ void DOS_Shell::CMD_PATH(char *args){
 
 void DOS_Shell::CMD_VER(char *args) {
 	HELP("VER");
-	if(args && *args) {
+	if(args && strlen(args)) {
 		char* word = StripWord(args);
 		if(strcasecmp(word,"set")) return;
 		word = StripWord(args);
diff --git a/src/shell/shell_misc.cpp b/src/shell/shell_misc.cpp
index e0282898..38702b90 100644
--- a/src/shell/shell_misc.cpp
+++ b/src/shell/shell_misc.cpp
@@ -254,11 +254,11 @@ void DOS_Shell::InputCommand(char * line) {
 
 					// build the completion list
 					char mask[DOS_PATHLENGTH] = {0};
-					if (strlen(p_completion_start) + 3 >= DOS_PATHLENGTH) {
-						//Beep;
-						break;
-					}
 					if (p_completion_start) {
+						if (strlen(p_completion_start) + 3 >= DOS_PATHLENGTH) {
+							//Beep;
+							break;
+						}
 						safe_strncpy(mask, p_completion_start,DOS_PATHLENGTH);
 						char* dot_pos=strrchr(mask,'.');
 						char* bs_pos=strrchr(mask,'\\');