From f9ccee5c4c6cb0d4197b08ebeb36c1dceffe82e8 Mon Sep 17 00:00:00 2001 From: Thorsten Kukuk Date: Thu, 14 Nov 2024 10:27:28 +0100 Subject: [PATCH] pam_access: rework resolving of tokens as hostname * modules/pam_access/pam_access.c: separate resolving of IP addresses from hostnames. Don't resolve TTYs or display variables as hostname (#834). Add "nodns" option to disallow resolving of tokens as hostname. * modules/pam_access/pam_access.8.xml: document nodns option * modules/pam_access/access.conf.5.xml: document that hostnames should be written as FQHN. Upstream-Status: Backport [https://github.com/linux-pam/linux-pam/commit/940747f88c16e029b69a74e80a2e94f65cb3e628] CVE: CVE-2024-10963 Signed-off-by: Stanislav Vovk --- modules/pam_access/access.conf.5.xml | 4 ++ modules/pam_access/pam_access.8.xml | 46 ++++++++++++------ modules/pam_access/pam_access.c | 72 +++++++++++++++++++++++++++- 3 files changed, 105 insertions(+), 17 deletions(-) diff --git a/modules/pam_access/access.conf.5.xml b/modules/pam_access/access.conf.5.xml index ff1cb223..158fc7df 100644 --- a/modules/pam_access/access.conf.5.xml +++ b/modules/pam_access/access.conf.5.xml @@ -220,10 +220,14 @@ the fields they are ignored. However if the list separator is changed with the listsep option, the spaces will become part of the actual item and the line will be most probably ignored. For this reason, it is not recommended to put spaces around the ':' characters. + + Hostnames should be written as Fully-Qualified Host Name (FQHN) to avoid + confusion with device names or PAM service names. + SEE ALSO diff --git a/modules/pam_access/pam_access.8.xml b/modules/pam_access/pam_access.8.xml index 010e749e..1182c907 100644 --- a/modules/pam_access/pam_access.8.xml +++ b/modules/pam_access/pam_access.8.xml @@ -20,15 +20,18 @@ pam_access.so debug + + noaudit + nodefgroup - noaudit + nodns accessfile=file @@ -127,10 +130,37 @@ Do not report logins from disallowed hosts and ttys to the audit subsystem. + + + nodefgroup + + + + User tokens which are not enclosed in parentheses will not be + matched against the group database. The backwards compatible default is + to try the group database match even for tokens not enclosed + in parentheses. + + + + + + + nodns + + + + Do not try to resolve tokens as hostnames, only IPv4 and IPv6 + addresses will be resolved. Which means to allow login from a + remote host, the IP addresses need to be specified in access.conf. + + + + fieldsep=separators @@ -168,24 +198,10 @@ "Domain Admins" contain a space. - - - nodefgroup - - - - User tokens which are not enclosed in parentheses will not be - matched against the group database. The backwards compatible default is - to try the group database match even for tokens not enclosed - in parentheses. - - - - MODULE TYPES PROVIDED diff --git a/modules/pam_access/pam_access.c b/modules/pam_access/pam_access.c index f70b7e49..d06496c3 100644 --- a/modules/pam_access/pam_access.c +++ b/modules/pam_access/pam_access.c @@ -97,10 +97,11 @@ struct login_info { const char *config_file; const char *hostname; int debug; /* Print debugging messages. */ int only_new_group_syntax; /* Only allow group entries of the form "(xyz)" */ int noaudit; /* Do not audit denials */ + int nodns; /* Do not try to resolve tokens as hostnames */ const char *fs; /* field separator */ const char *sep; /* list-element separator */ int from_remote_host; /* If PAM_RHOST was used for from */ struct addrinfo *res; /* Cached DNS resolution of from */ int gai_rv; /* Cached retval of getaddrinfo */ @@ -148,10 +149,12 @@ parse_args(pam_handle_t *pamh, struct login_info *loginfo, loginfo->debug = YES; } else if (strcmp (argv[i], "nodefgroup") == 0) { loginfo->only_new_group_syntax = YES; } else if (strcmp (argv[i], "noaudit") == 0) { loginfo->noaudit = YES; + } else if (strcmp (argv[i], "nodns") == 0) { + loginfo->nodns = YES; } else { pam_syslog(pamh, LOG_ERR, "unrecognized option [%s]", argv[i]); } } @@ -730,11 +733,11 @@ remote_match (pam_handle_t *pamh, char *tok, struct login_info *item) if (tok[0] == '.') { /* domain: match last fields */ if ((str_len = strlen(string)) > tok_len && strcasecmp(tok, string + str_len - tok_len) == 0) return YES; - } else if (tok[tok_len - 1] == '.') { /* internet network numbers (end with ".") */ + } else if (tok[tok_len - 1] == '.') { /* internet network numbers/subnet (end with ".") */ struct addrinfo hint; memset (&hint, '\0', sizeof (hint)); hint.ai_flags = AI_CANONNAME; hint.ai_family = AF_INET; @@ -805,10 +808,43 @@ string_match (pam_handle_t *pamh, const char *tok, const char *string, } return (NO); } +static int +is_device (pam_handle_t *pamh, const char *tok) +{ + struct stat st; + const char *dev = "/dev/"; + char *devname; + + devname = malloc (strlen(dev) + strlen (tok) + 1); + if (devname == NULL) { + pam_syslog(pamh, LOG_ERR, "Cannot allocate memory for device name: %m"); + /* + * We should return an error and abort, but pam_access has no good + * error handling. + */ + return NO; + } + + char *cp = stpcpy (devname, dev); + strcpy (cp, tok); + + if (lstat(devname, &st) != 0) + { + free (devname); + return NO; + } + free (devname); + + if (S_ISCHR(st.st_mode)) + return YES; + + return NO; +} + /* network_netmask_match - match a string against one token * where string is a hostname or ip (v4,v6) address and tok * represents either a hostname, a single ip (v4,v6) address * or a network/netmask */ @@ -866,14 +902,46 @@ network_netmask_match (pam_handle_t *pamh, if (getaddrinfo (tok, NULL, NULL, &ai) != 0) { return NO; } } + else if (isipaddr(tok, NULL, NULL) == YES) + { + if (getaddrinfo (tok, NULL, NULL, &ai) != 0) + { + if (item->debug) + pam_syslog(pamh, LOG_DEBUG, "cannot resolve IP address \"%s\"", tok); + + return NO; + } + netmask_ptr = NULL; + } + else if (item->nodns) + { + /* Only hostnames are left, which we would need to resolve via DNS */ + return NO; + } else { + /* Bail out on X11 Display entries and ttys. */ + if (tok[0] == ':') + { + if (item->debug) + pam_syslog (pamh, LOG_DEBUG, + "network_netmask_match: tok=%s is X11 display", tok); + return NO; + } + if (is_device (pamh, tok)) + { + if (item->debug) + pam_syslog (pamh, LOG_DEBUG, + "network_netmask_match: tok=%s is a TTY", tok); + return NO; + } + /* - * It is either an IP address or a hostname. + * It is most likely a hostname. * Let getaddrinfo sort everything out */ if (getaddrinfo (tok, NULL, NULL, &ai) != 0) { pam_syslog(pamh, LOG_ERR, "cannot resolve hostname \"%s\"", tok); -- 2.43.5