| // 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; |
| } |