edit: avoid potential crash with overlapping strings

In vi.c, there is a potential use of strcpy(3) on overlapping
strings, which is undefined behaviour:

> 	SHOPT_MULTIBYTE == 0
>
> 	# define gencpy(a,b)  strcpy((char*)(a),(char*)(b))
>
> 		.
> 		.
> 		.
>
> 	if( mode != 'y' )
> 	{
> 		gencpy(cp,cp+nchars);

Thanks to Heiko Berges for the report.

src/cmd/ksh93/edit/{edit,emacs,vi}.c:
- Change almost all use of strcpy(3) to libast strcopy(), which
  is a simple implementation that does not have a problem with
  overlapping strings. Note that the return value is different
  (it returns a pointer to the terminating '\0') but that is not
  relevant in any of these cases.
- Same for strncpy(3) => libast strncopy().

src/lib/libast/string/strcopy.c:
- Backport a couple of cosmetic tweaks from the 93v- beta.

src/cmd/ksh93/edit/edit.c

@@ -772,7 +772,7 @@ void	ed_setup(register Edit_t *ep, int fd, int reedit)
 		register int shift = 7-ep->e_wsize;
 		ep->e_wsize = 7;
 		pp = ep->e_prompt+1;
-		strcpy(pp,pp+shift);
+		strcopy(pp,pp+shift);
 		ep->e_plen -= shift;
 		last[-ep->e_plen-2] = '\r';
 	}
@@ -819,11 +819,11 @@ void	ed_setup(register Edit_t *ep, int fd, int reedit)
 #error no tput method
 #endif
 			if((pp = nv_getval(SH_SUBSCRNOD)) && strlen(pp) < sizeof(CURSOR_UP))
-				strcpy(CURSOR_UP,pp);
+				strcopy(CURSOR_UP,pp);
 			else
 				CURSOR_UP[0] = '\0';  /* no escape sequence is better than a faulty one */
 			nv_unset(SH_SUBSCRNOD);
-			strcpy(ep->e_termname,term);
+			strcopy(ep->e_termname,term);
 			sh.options = o;
 			sigrelease(SIGINT);
 		}
@@ -1493,7 +1493,7 @@ int	ed_external(const genchar *src, char *dest)
 #ifdef _lib_wcscpy
 		wcscpy((wchar_t *)dest,(const wchar_t *)buffer);
 #else
-		strcpy(dest,buffer);
+		strcopy(dest,buffer);
 #endif
 		return(c);
 	}
@@ -1662,7 +1662,7 @@ static int keytrap(Edit_t *ep,char *inbuff,register int insize, int bufsize, int
 		nv_unset(ED_CHRNOD);
 	else if(bufsize>0)
 	{
-		strncpy(inbuff,cp,bufsize);
+		strncopy(inbuff,cp,bufsize);
 		inbuff[bufsize-1]='\0';
 		insize = strlen(inbuff);
 	}

src/cmd/ksh93/edit/emacs.c

@@ -90,8 +90,8 @@ One line screen editor for any program
 #   define digit(c)	((c&~STRIP)==0 && isdigit(c))
 
 #else
-#   define gencpy(a,b)	strcpy((char*)(a),(char*)(b))
+#   define gencpy(a,b)	strcopy((char*)(a),(char*)(b))
-#   define genncpy(a,b,n)	strncpy((char*)(a),(char*)(b),n)
+#   define genncpy(a,b,n)	strncopy((char*)(a),(char*)(b),n)
 #   define genlen(str)	strlen(str)
 #   define print(c)	isprint(c)
 #   define isword(c)	(isalnum(out[c]) || (out[c]=='_'))
@@ -1425,7 +1425,7 @@ static void search(Emacs_t* ep,genchar *out,int direction)
 #if SHOPT_MULTIBYTE
 		ed_external(string,(char*)string);
 #endif /* SHOPT_MULTIBYTE */
-		strncpy(lstring,((char*)string)+2,SEARCHSIZE-1);
+		strncopy(lstring,((char*)string)+2,SEARCHSIZE-1);
 		lstring[SEARCHSIZE-1] = 0;
 		ep->prevdirection = direction;
 	}

src/cmd/ksh93/edit/history.c

@@ -1057,7 +1057,7 @@ char *hist_word(char *string,int size,int word)
 	*cp = 0;
 	if(s1 != string)
 		/* We can't use strcpy() because the two buffers may overlap. */
-		memmove(string,s1,strlen(s1)+1);
+		strcopy(string,s1);
 	return(string);
 }
 

src/cmd/ksh93/edit/vi.c

@@ -67,8 +67,8 @@
 #   define isalph(v)	_isalph(virtual[v])
 #else
     static genchar	_c;
-#   define gencpy(a,b)	strcpy((char*)(a),(char*)(b))
+#   define gencpy(a,b)	strcopy((char*)(a),(char*)(b))
-#   define genncpy(a,b,n) strncpy((char*)(a),(char*)(b),n)
+#   define genncpy(a,b,n) strncopy((char*)(a),(char*)(b),n)
 #   define genlen(str)	strlen(str)
 #   define isalph(v)	((_c=virtual[v])=='_'||isalnum(_c))
 #   undef  isblank
@@ -908,7 +908,7 @@ static int cntlmode(Vi_t *vp)
 				hist_copy((char*)virtual, MAXLINE, curhline,-1);
 			else
 			{
-				strcpy((char*)virtual,(char*)vp->u_space);
+				strcopy((char*)virtual,(char*)vp->u_space);
 #if SHOPT_MULTIBYTE
 				ed_internal((char*)vp->u_space,vp->u_space);
 #endif /* SHOPT_MULTIBYTE */
@@ -1634,7 +1634,7 @@ static int mvcursor(register Vi_t* vp,register int motion)
 #if SHOPT_MULTIBYTE
 				ed_external(virtual,lsearch+1);
 #else
-				strcpy(lsearch+1,virtual);
+				strcopy(lsearch+1,virtual);
 #endif /* SHOPT_MULTIBYTE */
 				*lsearch = '^';
 				vp->direction = -2;
@@ -2362,7 +2362,7 @@ static int search(register Vi_t* vp,register int mode)
 	{
 		/*** user wants repeat of last search ***/
 		del_line(vp,BAD);
-		strcpy( ((char*)virtual)+1, lsearch);
+		strcopy( ((char*)virtual)+1, lsearch);
 #if SHOPT_MULTIBYTE
 		*((char*)virtual) = '/';
 		ed_internal((char*)virtual,virtual);
@@ -2394,7 +2394,7 @@ static int search(register Vi_t* vp,register int mode)
 		location = hist_find(sh.hist_ptr,((char*)virtual)+1, curhline, 1, new_direction);
 	}
 	cur_virt = i;
-	strncpy(lsearch, ((char*)virtual)+1, SEARCHSIZE-1);
+	strncopy(lsearch, ((char*)virtual)+1, SEARCHSIZE-1);
 	lsearch[SEARCHSIZE-1] = 0;
 	if( (curhline=location.hist_command) >=0 )
 	{

src/lib/libast/string/strcopy.c

@@ -1,8 +1,8 @@
 /***********************************************************************
 *                                                                      *
 *               This software is part of the ast package               *
-*          Copyright (c) 1985-2011 AT&T Intellectual Property          *
+*          Copyright (c) 1985-2012 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2021 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2022 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 1.0                  *
 *                    by AT&T Intellectual Property                     *
@@ -30,7 +30,8 @@
 char*
 strcopy(register char* s, register const char* t)
 {
-	if (!t) return(s);
+	if (!t)
+		return s;
 	while (*s++ = *t++);
-	return(--s);
+	return s - 1;
 }