Rewrite environment-cleaning code to not directly modify environ or its contents.

The old code didn't work correctly with GNO's environ implementation and could lead to crashes.
This commit is contained in:
Stephen Heumann 2016-01-09 18:04:58 -06:00
parent e6c2831323
commit f659286e00
5 changed files with 132 additions and 58 deletions

View File

@ -21,6 +21,7 @@ TELNETD_SRCS = \
libtelnet/posix_openpt.c \ libtelnet/posix_openpt.c \
libtelnet/vasprintf.c \ libtelnet/vasprintf.c \
libtelnet/vfork.and.run.c \ libtelnet/vfork.and.run.c \
libtelnet/cleanenv.c \
telnetd/global.c \ telnetd/global.c \
telnetd/slc.c \ telnetd/slc.c \
telnetd/state.c \ telnetd/state.c \

117
libtelnet/cleanenv.c Normal file
View File

@ -0,0 +1,117 @@
/*-
* Copyright (c) 2016 Stephen Heumann
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <stdlib.h>
#include <string.h>
extern char **environ;
/*
* UNSETENV_REORDERS_ENVIRON must be set to 1 if unsetenv() may
* change entries in environ _prior to_ the one being removed.
* The implementation in GNO 2.0.6's libc doesn't do this,
* which allows us to optimize things a bit.
*/
#ifdef __GNO__
# define UNSETENV_REORDERS_ENVIRON 0
#else
# define UNSETENV_REORDERS_ENVIRON 1
#endif
/*
* Remove all environment entries except those indicated by retain,
* which is a null-terminated list of environment variable names.
*/
int cleanenv(const char *const retain[])
{
int index = 0;
const char *entry;
const char *const *keep;
while ((entry = environ[index]) != NULL) {
char *equals = strchr(entry, '=');
char *name;
if (equals) {
int match = 0;
size_t len = equals - entry + 1;
name = malloc(len);
if (name == NULL)
return -1;
strncpy(name, entry, len-1);
name[len-1] = 0;
for (keep = retain; *keep != NULL; keep++) {
if (strcmp(*keep, name) == 0) {
match = 1;
break;
}
}
if (match) {
index++;
free(name);
continue;
}
} else {
name = strdup(entry);
if (name == NULL)
return -1;
}
unsetenv(name);
free(name);
#if UNSETENV_REORDERS_ENVIRON
index = 0;
#endif
}
return 0;
}
#ifdef DEBUG_CLEANENV
#include <stdio.h>
void dump_env(const char *s)
{
int index;
const char *entry;
puts(s);
for (index = 0; (entry = environ[index]) != NULL; index++) {
puts(entry);
}
}
int main(void)
{
const char *retain[] = {"TERM", "USER", "PATH", "FOO", NULL};
dump_env("Before:");
cleanenv(retain);
dump_env("\nAfter:");
}
#endif

1
libtelnet/cleanenv.h Normal file
View File

@ -0,0 +1 @@
int cleanenv(const char *const retain[]);

View File

@ -52,6 +52,7 @@ static const char sccsid[] = "@(#)sys_term.c 8.4+1 (Berkeley) 5/30/95";
#include "telnetd.h" #include "telnetd.h"
#include "pathnames.h" #include "pathnames.h"
#include "libtelnet/vfork.and.run.h" #include "libtelnet/vfork.and.run.h"
#include "libtelnet/cleanenv.h"
#ifdef AUTHENTICATION #ifdef AUTHENTICATION
#include "libtelnet/auth.h" #include "libtelnet/auth.h"
@ -60,9 +61,6 @@ static const char sccsid[] = "@(#)sys_term.c 8.4+1 (Berkeley) 5/30/95";
int cleanopen(char *); int cleanopen(char *);
void scrub_env(void); void scrub_env(void);
char *envinit[3];
extern char **environ;
#define SCPYN(a, b) (void) strncpy(a, b, sizeof(a)) #define SCPYN(a, b) (void) strncpy(a, b, sizeof(a))
#define SCMPN(a, b) strncmp(a, b, sizeof(a)) #define SCMPN(a, b) strncmp(a, b, sizeof(a))
@ -996,13 +994,10 @@ startslave(char *host, int autologin, char *autoname)
void void
init_env(void) init_env(void)
{ {
char **envp; static const char *retain[] = {"TZ", NULL};
envp = envinit; if (cleanenv(retain) != 0)
if ((*envp = getenv("TZ"))) fatalperror(net, "Couldn't initialize environment");
*envp++ -= 3;
*envp = 0;
environ = envinit;
} }
@ -1232,58 +1227,19 @@ addarg(char **argv, const char *val)
void void
scrub_env(void) scrub_env(void)
{ {
static const char *rej[] = {
"TERMCAP=/",
NULL
};
static const char *acc[] = { static const char *acc[] = {
"XAUTH=", "XAUTHORITY=", "DISPLAY=", "XAUTH", "XAUTHORITY", "DISPLAY",
"TERM=", "TERM",
"EDITOR=", "EDITOR",
"PAGER=", "PAGER",
"LOGNAME=", "LOGNAME",
"POSIXLY_CORRECT=", "POSIXLY_CORRECT",
"PRINTER=", "PRINTER",
NULL NULL
}; };
char **cpp, **cpp2; if (cleanenv(acc) != 0)
const char **p; fatalperror(net, "Couldn't initialize environment");
char ** new_environ;
size_t count;
/* Allocate space for scrubbed environment. */
for (count = 1, cpp = environ; *cpp; count++, cpp++)
continue;
if ((new_environ = malloc(count * sizeof(char *))) == NULL) {
environ = NULL;
return;
}
for (cpp2 = new_environ, cpp = environ; *cpp; cpp++) {
int reject_it = 0;
for(p = rej; *p; p++)
if(strncmp(*cpp, *p, strlen(*p)) == 0) {
reject_it = 1;
break;
}
if (reject_it)
continue;
for(p = acc; *p; p++)
if(strncmp(*cpp, *p, strlen(*p)) == 0)
break;
if(*p != NULL) {
if ((*cpp2++ = strdup(*cpp)) == NULL) {
environ = new_environ;
return;
}
}
}
*cpp2 = NULL;
environ = new_environ;
} }

View File

@ -45,5 +45,4 @@
#endif #endif
/* other external variables */ /* other external variables */
extern char **environ;
extern const char *altlogin; extern const char *altlogin;