Re: [PATCH] capabilities: introduce per-process capability bounding set (v10)

[Andrew Morgan <morgan@kernel.org>]

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There is already a pam_cap module in the libcap2 package. Can we merge
this functionality?

Cheers

Andrew

serge@hallyn.com wrote:
> Quoting KaiGai Kohei (kaigai@kaigai.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@masu ~]$ 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@masu ~]$ ssh tak@localhost
>> tak@localhost's password:
>> Last login: Sat Dec  1 10:09:29 2007 from masu.myhome.cx
>> [tak@masu ~]$ export LANG=C
>> [tak@masu ~]$ ping 192.168.1.1
>> ping: icmp open socket: Operation not permitted
>>
>> [tak@masu ~]$ su
>> Password:
>> pam_cap_bset[6921]: user root does not have 'cap_drop=' property
>> [root@masu tak]# cat /proc/self/status | grep ^Cap
>> CapInh: 0000000000000000
>> CapPrm: 00000000ffffdffe
>> CapEff: 00000000ffffdffe
>> [root@masu 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@kaigai.gr.jp>
>>
>> ************************************************************
>>     pam_cap_drop.c
>> ************************************************************
>>
>> /*
>>  * pam_cap_drop.c module -- drop capabilities bounding set
>>  *
>>  * Copyright: 2007 KaiGai Kohei <kaigai@kaigai.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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