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Date: Sat, 01 Dec 2007 11:10:59 -0800
From: Andrew Morgan <morgan@...nel.org>
To: serge@...lyn.com, KaiGai Kohei <kaigai@...gai.gr.jp>
CC: "Serge E. Hallyn" <serue@...ibm.com>,
lkml <linux-kernel@...r.kernel.org>,
linux-security-module@...r.kernel.org,
Chris Wright <chrisw@...s-sol.org>,
Stephen Smalley <sds@...ch.ncsc.mil>,
James Morris <jmorris@...ei.org>, Andrew Morton <akpm@...l.org>
Subject: Re: [PATCH] capabilities: introduce per-process capability bounding
set (v10)
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There is already a pam_cap module in the libcap2 package. Can we merge
this functionality?
Cheers
Andrew
serge@...lyn.com wrote:
> Quoting KaiGai Kohei (kaigai@...gai.gr.jp):
>> Serge E. Hallyn wrote:
>>> The capability bounding set is a set beyond which capabilities
>>> cannot grow. Currently cap_bset is per-system. It can be
>>> manipulated through sysctl, but only init can add capabilities.
>>> Root can remove capabilities. By default it includes all caps
>>> except CAP_SETPCAP.
>> Serge,
>>
>> This feature makes me being interested in.
>> I think you intend to apply this feature for the primary process
>> of security container.
>> However, it is also worthwhile to apply when a session is starting up.
>>
>> The following PAM module enables to drop capability bounding bit
>> specified by the fifth field in /etc/passwd entry.
>> This code is just an example now, but considerable feature.
>>
>> build and install:
>> # gcc -Wall -c pam_cap_drop.c
>> # gcc -Wall -shared -Xlinker -x -o pam_cap_drop.so pam_cap_drop.o -lpam
>> # cp pam_cap_drop.so /lib/security
>>
>> modify /etc/passwd as follows:
>>
>> tak:x:1004:100:cap_drop=cap_net_raw,cap_chown:/home/tak:/bin/bash
>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> example:
>> [kaigai@...u ~]$ ping 192.168.1.1
>> PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
>> 64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=1.23 ms
>> 64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=1.02 ms
>>
>> --- 192.168.1.1 ping statistics ---
>> 2 packets transmitted, 2 received, 0% packet loss, time 999ms
>> rtt min/avg/max/mdev = 1.023/1.130/1.237/0.107 ms
>>
>> [kaigai@...u ~]$ ssh tak@...alhost
>> tak@...alhost's password:
>> Last login: Sat Dec 1 10:09:29 2007 from masu.myhome.cx
>> [tak@...u ~]$ export LANG=C
>> [tak@...u ~]$ ping 192.168.1.1
>> ping: icmp open socket: Operation not permitted
>>
>> [tak@...u ~]$ su
>> Password:
>> pam_cap_bset[6921]: user root does not have 'cap_drop=' property
>> [root@...u tak]# cat /proc/self/status | grep ^Cap
>> CapInh: 0000000000000000
>> CapPrm: 00000000ffffdffe
>> CapEff: 00000000ffffdffe
>> [root@...u tak]#
>
> Neat. A bigger-stick version of not adding the account to
> group wheel. I'll use that.
>
> Is there any reason not to have a separate /etc/login.capbounds
> config file, though, so the account can still have a full name?
> Did you only use that for convenience of proof of concept, or
> is there another reason?
>
>> # BTW, I replaced the James's address in the Cc: list,
>> # because MTA does not accept it.
>
> Thanks! I don't know what happened to my alias for him...
>
> thanks,
> -serge
>
>> --
>> KaiGai Kohei <kaigai@...gai.gr.jp>
>>
>> ************************************************************
>> pam_cap_drop.c
>> ************************************************************
>>
>> /*
>> * pam_cap_drop.c module -- drop capabilities bounding set
>> *
>> * Copyright: 2007 KaiGai Kohei <kaigai@...gai.gr.jp>
>> */
>>
>> #include <errno.h>
>> #include <pwd.h>
>> #include <stdlib.h>
>> #include <stdio.h>
>> #include <string.h>
>> #include <syslog.h>
>> #include <sys/prctl.h>
>> #include <sys/types.h>
>>
>> #include <security/pam_modules.h>
>>
>> #ifndef PR_CAPBSET_DROP
>> #define PR_CAPBSET_DROP 24
>> #endif
>>
>> static char *captable[] = {
>> "cap_chown",
>> "cap_dac_override",
>> "cap_dac_read_search",
>> "cap_fowner",
>> "cap_fsetid",
>> "cap_kill",
>> "cap_setgid",
>> "cap_setuid",
>> "cap_setpcap",
>> "cap_linux_immutable",
>> "cap_net_bind_service",
>> "cap_net_broadcast",
>> "cap_net_admin",
>> "cap_net_raw",
>> "cap_ipc_lock",
>> "cap_ipc_owner",
>> "cap_sys_module",
>> "cap_sys_rawio",
>> "cap_sys_chroot",
>> "cap_sys_ptrace",
>> "cap_sys_pacct",
>> "cap_sys_admin",
>> "cap_sys_boot",
>> "cap_sys_nice",
>> "cap_sys_resource",
>> "cap_sys_time",
>> "cap_sys_tty_config",
>> "cap_mknod",
>> "cap_lease",
>> "cap_audit_write",
>> "cap_audit_control",
>> "cap_setfcap",
>> NULL,
>> };
>>
>>
>> PAM_EXTERN int
>> pam_sm_open_session(pam_handle_t *pamh, int flags,
>> int argc, const char **argv)
>> {
>> struct passwd *pwd;
>> char *pos, *buf;
>> char *username = NULL;
>>
>> /* open system logger */
>> openlog("pam_cap_bset", LOG_PERROR | LOG_PID, LOG_AUTHPRIV);
>>
>> /* get the unix username */
>> if (pam_get_item(pamh, PAM_USER, (void *) &username) != PAM_SUCCESS || !username)
>> return PAM_USER_UNKNOWN;
>>
>> /* get the passwd entry */
>> pwd = getpwnam(username);
>> if (!pwd)
>> return PAM_USER_UNKNOWN;
>>
>> /* Is there "cap_drop=" ? */
>> pos = strstr(pwd->pw_gecos, "cap_drop=");
>> if (pos) {
>> buf = strdup(pos + sizeof("cap_drop=") - 1);
>> if (!buf)
>> return PAM_SESSION_ERR;
>> pos = strtok(buf, ",");
>> while (pos) {
>> int rc, i;
>>
>> for (i=0; captable[i]; i++) {
>> if (!strcmp(pos, captable[i])) {
>> rc = prctl(PR_CAPBSET_DROP, i);
>> if (rc < 0) {
>> syslog(LOG_NOTICE, "user %s could not drop %s (%s)",
>> username, captable[i], strerror(errno));
>> break;
>> }
>> syslog(LOG_NOTICE, "user %s drops %s\n", username, captable[i]);
>> goto next;
>> }
>> }
>> break;
>> next:
>> pos = strtok(NULL, ",");
>> }
>> free(buf);
>> } else {
>> syslog(LOG_NOTICE, "user %s does not have 'cap_drop=' property", username);
>> }
>> return PAM_SUCCESS;
>> }
>>
>> PAM_EXTERN int
>> pam_sm_close_session(pam_handle_t *pamh, int flags,
>> int argc, const char **argv)
>> {
>> /* do nothing */
>> return PAM_SUCCESS;
>> }
>>
>> ************************************************************
>> -
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