Avoid importing env vars with invalid names (rhbz#1147645)

This imports a new version of the code to import environment
variable values that was sent to Red Hat from upstream in 2014.
It avoids importing environment variables whose names are not valid
in the shell language, as it would be impossible to change or unset
them. However, they stay in the environment to be passed to child
processes.

Prior discussion: https://bugzilla.redhat.com/1147645
Original patch: https://src.fedoraproject.org/rpms/ksh/blob/642af4d6/f/ksh-20120801-oldenvinit.patch

src/cmd/ksh93/sh/init.c:

- env_init(): Import new, simplified code to import environment
  variable name/value pairs. Instead of doing the heavy lifting
  itself, this version uses nv_open(), passing the NV_IDENT flag to
  reject and skip invalid names.

- Get rid of gotos and a static var by splitting off the code to
  import attributes into a new env_import_attributes() function.
  This is a better way to avoid importing attributes when
  initialising the shell in POSIX mode (re: 00d4396

- Remove an nv_mapchar() call that was based on some unclear
  flaggery which was also removed by upstream as sent to Red Hat.
  I don't know what that did, if anything; looks like it might have
  had something to do with typeset -u/-l, but those particular
  attributes have never been successfully inherited through the
  environment.
    (Maybe that's another bug, or maybe I just don't care as
    inheriting attributes is a misfeature anyway; we have to put up
    with it because legacy scripts might use it. Maybe someone can
    prove it's an unacceptable security risk to import attributes
    like readonly from an environment variable that is inherently
    vulnerable to manipulation. That would be nice, as a CVE ID
    would give us a solid reason to get rid of this nonsense.)

- Remove an 'else cp += 2;' that was very clearly a no-op; 'cp' is
  immediately overwritten on the next loop iteration and not used
  past the loop.

src/cmd/ksh93/tests/variables.sh:

- Test.

NEWS

@@ -7,6 +7,10 @@ Any uppercase BUG_* names are modernish shell bug IDs.
 
 - 'whence -f' now completely ignores the existence of functions, as documented.
 
+- ksh now does not import environment variables whose names are not valid in
+  the shell language, as it would be impossible to change or unset them.
+  However, they stay in the environment to be passed to child processes.
+
 2020-09-25:
 
 - whence -v/-a now reports the path to the file that an "undefined" (i.e.

src/cmd/ksh93/sh/init.c

@@ -199,7 +199,8 @@ typedef struct _init_
 static Init_t		*ip;
 static int		lctype;
 static int		nbltins;
-static void		env_init(Shell_t*,int);
+static char		*env_init(Shell_t*);
+static void		env_import_attributes(Shell_t*,char*);
 static Init_t		*nv_init(Shell_t*);
 static int		shlvl;
 
@@ -1179,6 +1180,7 @@ Shell_t *sh_init(register int argc,register char *argv[], Shinit_f userinit)
 	Shell_t	*shp;
 	register int n;
 	int type;
+	char *save_envmarker;
 	static char *login_files[3];
 	memfatal();
 	n = strlen(e_version);
@@ -1293,8 +1295,8 @@ Shell_t *sh_init(register int argc,register char *argv[], Shinit_f userinit)
 		if(type&SH_TYPE_POSIX)
 			sh_onoption(SH_POSIX);
 	}
-	/* read the environment; don't import attributes yet */
-	env_init(shp,0);
+	/* read the environment; don't import attributes yet, but save pointer to them */
+	save_envmarker = env_init(shp);
 	if(!ENVNOD->nvalue.cp)
 	{
 		sfprintf(shp->strbuf,"%s/.kshrc",nv_getval(HOME));
@@ -1397,7 +1399,7 @@ Shell_t *sh_init(register int argc,register char *argv[], Shinit_f userinit)
 	}
 	/* import variable attributes from environment */
 	if(!sh_isoption(SH_POSIX))
-		env_init(shp,1);
+		env_import_attributes(shp,save_envmarker);
 #if SHOPT_PFSH
 	if (sh_isoption(SH_PFSH))
 	{
@@ -1883,86 +1885,53 @@ Dt_t *sh_inittree(Shell_t *shp,const struct shtable2 *name_vals)
  * read in the process environment and set up name-value pairs
  * skip over items that are not name-value pairs
  *
- * Must be called with import_attributes == 0 first, then again with
- * import_attributes == 1 if variable attributes are to be imported
- * from the environment.
+ * Returns pointer to A__z env var from which to import attributes, or 0.
  */
 
-static void env_init(Shell_t *shp, int import_attributes)
+static char *env_init(Shell_t *shp)
 {
 	register char		*cp;
-	register Namval_t	*np,*mp;
+	register Namval_t	*np;
 	register char		**ep=environ;
-	char			*dp;
-	int			nenv=0,k=0,size=0;
-	Namval_t		*np0;
-	static char		*next=0;  /* next variable whose attributes to import */
-
-	if(import_attributes)
-		goto import_attributes;
-	if(!ep)
-		goto skip;
-	while(*ep++)
-		nenv++;
-	np = newof(0,Namval_t,nenv,0);
-	for(np0=np,ep=environ;cp= *ep; ep++)
+	char			*next = 0;	/* pointer to A__z env var */
+	if(ep)
 	{
-		dp = strchr(cp,'=');
-		if(!dp)
-			continue;
-		*dp++ = 0;
-		if(mp = dtmatch(shp->var_base,cp))
-		{
-			mp->nvenv = (char*)cp;
-			dp[-1] = '=';
-		}
-		else if(strcmp(cp,e_envmarker)==0)
-		{
-			dp[-1] = '=';
-			next = cp + strlen(e_envmarker);
-			continue;
-		}
-		else
-		{
-			k++;
-			mp = np++;
-			mp->nvname = cp;
-			size += strlen(cp);
-		}
-		nv_onattr(mp,NV_IMPORT);
-		if(mp->nvfun || nv_isattr(mp,NV_INTEGER))
-			nv_putval(mp,dp,0);
-		else
+		while(cp = *ep++)
 		{
-			mp->nvalue.cp = dp;
-			nv_onattr(mp,NV_NOFREE);
+			/* The magic A__z env var is an invention of ksh88. See e_envmarker[]. */
+			if(*cp=='A' && cp[1]=='_' && cp[2]=='_' && cp[3]=='z' && cp[4]=='=')
+				next = cp + 4;
+			else if(np = nv_open(cp,shp->var_tree,(NV_EXPORT|NV_IDENT|NV_ASSIGN|NV_NOFAIL)))
+			{
+				nv_onattr(np,NV_IMPORT);
+				np->nvenv = cp;
+				nv_close(np);
+			}
+			else  /* swap with front */
+			{
+				ep[-1] = environ[shp->nenv];
+				environ[shp->nenv++] = cp;
+			}
 		}
-		nv_onattr(mp,NV_EXPORT|NV_IMPORT);
-	}
-	np =  (Namval_t*)realloc((void*)np0,k*sizeof(Namval_t));
-	dp = (char*)malloc(size+k);
-	while(k-->0)
-	{
-		size = strlen(np->nvname);
-		memcpy(dp,np->nvname,size+1);
-		np->nvname[size] = '=';
-		np->nvenv = np->nvname;
-		np->nvname = dp;
-		dp += size+1;
-		dtinsert(shp->var_base,np++);
 	}
-skip:
 	if(nv_isnull(PWDNOD) || nv_isattr(PWDNOD,NV_TAGGED))
 	{
 		nv_offattr(PWDNOD,NV_TAGGED);
 		path_pwd(shp,0);
 	}
 	if((cp = nv_getval(SHELLNOD)) && (sh_type(cp)&SH_TYPE_RESTRICTED))
 		sh_onoption(SH_RESTRICTED); /* restricted shell */
-	return;
+	return(next);
+}
 
-	/* Import variable attributes from environment (from variable named by e_envmarker) */
-import_attributes:
+/*
+ * Import variable attributes from magic A__z env var pointed to by 'next'.
+ * If next == 0, this function does nothing.
+ */
+static void env_import_attributes(Shell_t *shp, char *next)
+{
+	register char		*cp;
+	register Namval_t	*np;
 	while(cp=next)
 	{
 		if(next = strchr(++cp,'='))
@@ -1975,7 +1944,7 @@ static void env_init(Shell_t *shp, int import_attributes)
 			if((flag&NV_INTEGER) && size==0)
 			{
 				/* check for floating*/
-				char *val = nv_getval(np);
+				char *dp, *val = nv_getval(np);
 				strtol(val,&dp,10);
 				if(*dp=='.' || *dp=='e' || *dp=='E')
 				{
@@ -1998,11 +1967,7 @@ static void env_init(Shell_t *shp, int import_attributes)
 				}
 			}
 			nv_newattr(np,flag|NV_IMPORT|NV_EXPORT,size);
-			if((flag&(NV_INTEGER|NV_UTOL|NV_LTOU))==(NV_UTOL|NV_LTOU))
-				nv_mapchar(np,(flag&NV_UTOL)?e_tolower:e_toupper);
 		}
-		else
-			cp += 2;
 	}
 	return;
 }

src/cmd/ksh93/tests/variables.sh

@@ -1123,5 +1123,12 @@ do	for word in '(word)' 'w(or)d' '(wor)d' 'w(ord)' 'w(ord' 'wor)d'
 	done
 done
 
+# ======
+# https://bugzilla.redhat.com/1147645
+case $'\n'$(env 'BASH_FUNC_a%%=() { echo test; }' "$SHELL" -c set) in
+*$'\nBASH_FUNC_a%%='* )
+	err_exit 'ksh imports environment variables with invalid names' ;;
+esac
+
 # ======
 exit $((Errors<125?Errors:125))