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