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// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// sshd_test_pw.c
// Wrapper to inject test password data for sshd PAM authentication
//
// This wrapper implements custom versions of getpwnam, getpwnam_r,
// getspnam and getspnam_r. These functions first call their real
// libc versions, then check if the requested user matches test user
// specified in env variable TEST_USER and if so replace the password
// with crypted() value of TEST_PASSWD env variable.
//
// Compile:
// gcc -Wall -shared -o sshd_test_pw.so -fPIC sshd_test_pw.c
//
// Compile with debug:
// gcc -DVERBOSE -Wall -shared -o sshd_test_pw.so -fPIC sshd_test_pw.c
//
// Run sshd:
// LD_PRELOAD="sshd_test_pw.so" TEST_USER="..." TEST_PASSWD="..." sshd ...
// +build ignore
#define _GNU_SOURCE
#include <string.h>
#include <pwd.h>
#include <shadow.h>
#include <dlfcn.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#ifdef VERBOSE
#define DEBUG(X...) fprintf(stderr, X)
#else
#define DEBUG(X...) while (0) { }
#endif
/* crypt() password */
static char *
pwhash(char *passwd) {
return strdup(crypt(passwd, "$6$"));
}
/* Pointers to real functions in libc */
static struct passwd * (*real_getpwnam)(const char *) = NULL;
static int (*real_getpwnam_r)(const char *, struct passwd *, char *, size_t, struct passwd **) = NULL;
static struct spwd * (*real_getspnam)(const char *) = NULL;
static int (*real_getspnam_r)(const char *, struct spwd *, char *, size_t, struct spwd **) = NULL;
/* Cached test user and test password */
static char *test_user = NULL;
static char *test_passwd_hash = NULL;
static void
init(void) {
/* Fetch real libc function pointers */
real_getpwnam = dlsym(RTLD_NEXT, "getpwnam");
real_getpwnam_r = dlsym(RTLD_NEXT, "getpwnam_r");
real_getspnam = dlsym(RTLD_NEXT, "getspnam");
real_getspnam_r = dlsym(RTLD_NEXT, "getspnam_r");
/* abort if env variables are not defined */
if (getenv("TEST_USER") == NULL || getenv("TEST_PASSWD") == NULL) {
fprintf(stderr, "env variables TEST_USER and TEST_PASSWD are missing\n");
abort();
}
/* Fetch test user and test password from env */
test_user = strdup(getenv("TEST_USER"));
test_passwd_hash = pwhash(getenv("TEST_PASSWD"));
DEBUG("sshd_test_pw init():\n");
DEBUG("\treal_getpwnam: %p\n", real_getpwnam);
DEBUG("\treal_getpwnam_r: %p\n", real_getpwnam_r);
DEBUG("\treal_getspnam: %p\n", real_getspnam);
DEBUG("\treal_getspnam_r: %p\n", real_getspnam_r);
DEBUG("\tTEST_USER: '%s'\n", test_user);
DEBUG("\tTEST_PASSWD: '%s'\n", getenv("TEST_PASSWD"));
DEBUG("\tTEST_PASSWD_HASH: '%s'\n", test_passwd_hash);
}
static int
is_test_user(const char *name) {
if (test_user != NULL && strcmp(test_user, name) == 0)
return 1;
return 0;
}
/* getpwnam */
struct passwd *
getpwnam(const char *name) {
struct passwd *pw;
DEBUG("sshd_test_pw getpwnam(%s)\n", name);
if (real_getpwnam == NULL)
init();
if ((pw = real_getpwnam(name)) == NULL)
return NULL;
if (is_test_user(name))
pw->pw_passwd = strdup(test_passwd_hash);
return pw;
}
/* getpwnam_r */
int
getpwnam_r(const char *name,
struct passwd *pwd,
char *buf,
size_t buflen,
struct passwd **result) {
int r;
DEBUG("sshd_test_pw getpwnam_r(%s)\n", name);
if (real_getpwnam_r == NULL)
init();
if ((r = real_getpwnam_r(name, pwd, buf, buflen, result)) != 0 || *result == NULL)
return r;
if (is_test_user(name))
pwd->pw_passwd = strdup(test_passwd_hash);
return 0;
}
/* getspnam */
struct spwd *
getspnam(const char *name) {
struct spwd *sp;
DEBUG("sshd_test_pw getspnam(%s)\n", name);
if (real_getspnam == NULL)
init();
if ((sp = real_getspnam(name)) == NULL)
return NULL;
if (is_test_user(name))
sp->sp_pwdp = strdup(test_passwd_hash);
return sp;
}
/* getspnam_r */
int
getspnam_r(const char *name,
struct spwd *spbuf,
char *buf,
size_t buflen,
struct spwd **spbufp) {
int r;
DEBUG("sshd_test_pw getspnam_r(%s)\n", name);
if (real_getspnam_r == NULL)
init();
if ((r = real_getspnam_r(name, spbuf, buf, buflen, spbufp)) != 0)
return r;
if (is_test_user(name))
spbuf->sp_pwdp = strdup(test_passwd_hash);
return r;
}
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