/* $OpenBSD: auth-rhosts.c,v 1.56 2022/02/23 21:21:49 djm Exp $ */ /* * Author: Tatu Ylonen * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland * All rights reserved * Rhosts authentication. This file contains code to check whether to admit * the login based on rhosts authentication. This file also processes * /etc/hosts.equiv. * * As far as I am concerned, the code I have written for this software * can be used freely for any purpose. Any derived versions of this * software must be clearly marked as such, and if the derived work is * incompatible with the protocol description in the RFC file, it must be * called by a name other than "ssh" or "Secure Shell". */ #include #include #include #include #include #include #include #include #include #include #include "packet.h" #include "uidswap.h" #include "pathnames.h" #include "log.h" #include "misc.h" #include "xmalloc.h" #include "sshbuf.h" #include "sshkey.h" #include "servconf.h" #include "canohost.h" #include "hostfile.h" #include "auth.h" /* import */ extern ServerOptions options; extern int use_privsep; /* * This function processes an rhosts-style file (.rhosts, .shosts, or * /etc/hosts.equiv). This returns true if authentication can be granted * based on the file, and returns zero otherwise. */ static int check_rhosts_file(const char *filename, const char *hostname, const char *ipaddr, const char *client_user, const char *server_user) { FILE *f; #define RBUFLN 1024 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */ int fd; struct stat st; /* Open the .rhosts file, deny if unreadable */ if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) return 0; if (fstat(fd, &st) == -1) { close(fd); return 0; } if (!S_ISREG(st.st_mode)) { logit("User %s hosts file %s is not a regular file", server_user, filename); close(fd); return 0; } unset_nonblock(fd); if ((f = fdopen(fd, "r")) == NULL) { close(fd); return 0; } while (fgets(buf, sizeof(buf), f)) { /* All three must have length >= buf to avoid overflows. */ char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN]; char *host, *user, *cp; int negated; for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) ; if (*cp == '#' || *cp == '\n' || !*cp) continue; /* * NO_PLUS is supported at least on OSF/1. We skip it (we * don't ever support the plus syntax). */ if (strncmp(cp, "NO_PLUS", 7) == 0) continue; /* * This should be safe because each buffer is as big as the * whole string, and thus cannot be overwritten. */ switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf, dummy)) { case 0: auth_debug_add("Found empty line in %.100s.", filename); continue; case 1: /* Host name only. */ strlcpy(userbuf, server_user, sizeof(userbuf)); break; case 2: /* Got both host and user name. */ break; case 3: auth_debug_add("Found garbage in %.100s.", filename); continue; default: /* Weird... */ continue; } host = hostbuf; user = userbuf; negated = 0; /* Process negated host names, or positive netgroups. */ if (host[0] == '-') { negated = 1; host++; } else if (host[0] == '+') host++; if (user[0] == '-') { negated = 1; user++; } else if (user[0] == '+') user++; /* Check for empty host/user names (particularly '+'). */ if (!host[0] || !user[0]) { /* We come here if either was '+' or '-'. */ auth_debug_add("Ignoring wild host/user names " "in %.100s.", filename); continue; } /* Verify that host name matches. */ if (host[0] == '@') { if (!innetgr(host + 1, hostname, NULL, NULL) && !innetgr(host + 1, ipaddr, NULL, NULL)) continue; } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0) continue; /* Different hostname. */ /* Verify that user name matches. */ if (user[0] == '@') { if (!innetgr(user + 1, NULL, client_user, NULL)) continue; } else if (strcmp(user, client_user) != 0) continue; /* Different username. */ /* Found the user and host. */ fclose(f); /* If the entry was negated, deny access. */ if (negated) { auth_debug_add("Matched negative entry in %.100s.", filename); return 0; } /* Accept authentication. */ return 1; } /* Authentication using this file denied. */ fclose(f); return 0; } /* * Tries to authenticate the user using the .shosts or .rhosts file. Returns * true if authentication succeeds. If ignore_rhosts is true, only * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). */ int auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, const char *ipaddr) { char *path = NULL; struct stat st; static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL}; u_int rhosts_file_index; int r; debug2_f("clientuser %s hostname %s ipaddr %s", client_user, hostname, ipaddr); /* Switch to the user's uid. */ temporarily_use_uid(pw); /* * Quick check: if the user has no .shosts or .rhosts files and * no system hosts.equiv/shosts.equiv files exist then return * failure immediately without doing costly lookups from name * servers. */ for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; rhosts_file_index++) { /* Check users .rhosts or .shosts. */ xasprintf(&path, "%s/%s", pw->pw_dir, rhosts_files[rhosts_file_index]); r = stat(path, &st); free(path); if (r >= 0) break; } /* Switch back to privileged uid. */ restore_uid(); /* * Deny if The user has no .shosts or .rhosts file and there * are no system-wide files. */ if (!rhosts_files[rhosts_file_index] && stat(_PATH_RHOSTS_EQUIV, &st) == -1 && stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) { debug3_f("no hosts access files exist"); return 0; } /* * If not logging in as superuser, try /etc/hosts.equiv and * shosts.equiv. */ if (pw->pw_uid == 0) debug3_f("root user, ignoring system hosts files"); else { if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, client_user, pw->pw_name)) { auth_debug_add("Accepted for %.100s [%.100s] by " "/etc/hosts.equiv.", hostname, ipaddr); return 1; } if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, client_user, pw->pw_name)) { auth_debug_add("Accepted for %.100s [%.100s] by " "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); return 1; } } /* * Check that the home directory is owned by root or the user, and is * not group or world writable. */ if (stat(pw->pw_dir, &st) == -1) { logit("Rhosts authentication refused for %.100s: " "no home directory %.200s", pw->pw_name, pw->pw_dir); auth_debug_add("Rhosts authentication refused for %.100s: " "no home directory %.200s", pw->pw_name, pw->pw_dir); return 0; } if (options.strict_modes && ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || (st.st_mode & 022) != 0)) { logit("Rhosts authentication refused for %.100s: " "bad ownership or modes for home directory.", pw->pw_name); auth_debug_add("Rhosts authentication refused for %.100s: " "bad ownership or modes for home directory.", pw->pw_name); return 0; } /* Temporarily use the user's uid. */ temporarily_use_uid(pw); /* Check all .rhosts files (currently .shosts and .rhosts). */ for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; rhosts_file_index++) { /* Check users .rhosts or .shosts. */ xasprintf(&path, "%s/%s", pw->pw_dir, rhosts_files[rhosts_file_index]); if (stat(path, &st) == -1) { free(path); continue; } /* * Make sure that the file is either owned by the user or by * root, and make sure it is not writable by anyone but the * owner. This is to help avoid novices accidentally * allowing access to their account by anyone. */ if (options.strict_modes && ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || (st.st_mode & 022) != 0)) { logit("Rhosts authentication refused for %.100s: " "bad modes for %.200s", pw->pw_name, path); auth_debug_add("Bad file modes for %.200s", path); free(path); continue; } /* * Check if we have been configured to ignore .rhosts * and .shosts files. */ if (options.ignore_rhosts == IGNORE_RHOSTS_YES || (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS && strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) { auth_debug_add("Server has been configured to " "ignore %.100s.", rhosts_files[rhosts_file_index]); free(path); continue; } /* Check if authentication is permitted by the file. */ if (check_rhosts_file(path, hostname, ipaddr, client_user, pw->pw_name)) { auth_debug_add("Accepted by %.100s.", rhosts_files[rhosts_file_index]); /* Restore the privileged uid. */ restore_uid(); auth_debug_add("Accepted host %s ip %s client_user " "%s server_user %s", hostname, ipaddr, client_user, pw->pw_name); free(path); return 1; } free(path); } /* Restore the privileged uid. */ restore_uid(); return 0; }