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/* -*- linux-c -*-
*
* cap.c - staprun capabilities functions
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) 2007 Red Hat, Inc.
*
*/
#include "staprun.h"
#include <sys/prctl.h>
static int _stp_no_caps = 0;
/* like perror, but exits */
#define ferror(msg) { \
_perr(msg); \
exit(1); \
} \
/*
* init_cap() sets up the initial capabilities for staprun. Then
* it calls prctl( PR_SET_KEEPCAPS) to arrrange to keep these capabilities
* even when not running as root. Next it resets the real, effective, and
* saved uid and gid back to the normal user.
*
* There are two sets of capabilities we are concerned with; permitted
* and effective. The permitted capabilities are all the capabilities
* that this process is ever permitted to have. They are defined in init_cap()
* and may be permanently removed with drop_cap().
*
* Effective capabilities are the capabilities from the permitted set
* that are currently enabled. A good practice would be to only enable
* capabilities when necessary and to delete or drop them as soon as possible.
*
* Capabilities we might use include:
*
* CAP_SYS_MODULE - insert and remove kernel modules
* CAP_SYS_ADMIN - misc, including mounting and unmounting
* CAP_SYS_NICE - setpriority()
* CAP_SETUID - allows setuid
* CAP_SETGID - allows setgid
* CAP_CHOWN - allows chown
*/
void init_cap(void)
{
cap_t caps = cap_init();
cap_value_t capv[] = { CAP_SYS_MODULE, CAP_SYS_ADMIN, CAP_SYS_NICE, CAP_SETUID, CAP_SETGID, CAP_DAC_OVERRIDE };
const int numcaps = sizeof(capv) / sizeof(capv[0]);
uid_t uid = getuid();
gid_t gid = getgid();
cap_clear(caps);
if (caps == NULL)
ferror("cap_init");
if (cap_set_flag(caps, CAP_PERMITTED, numcaps, capv, CAP_SET) < 0)
ferror("cap_set_flag");
if (cap_set_proc(caps) < 0) {
dbug(1, "Setting capabilities failed. Capabilities disabled.\n");
_stp_no_caps = 1;
return;
}
cap_free(caps);
if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) < 0)
ferror("prctl");
if (setresuid(uid, uid, uid) < 0)
ferror("setresuid");
if (setresgid(gid, gid, gid) < 0)
ferror("setresgid");
}
void print_cap(char *text)
{
int p;
cap_t caps = cap_get_proc();
uid_t uid, euid, suid;
gid_t gid, egid, sgid;
if (caps == NULL) {
perr("cap_get_proc");
return;
}
getresuid(&uid, &euid, &suid);
getresgid(&gid, &egid, &sgid);
printf("***** %s\n", text);
if ((p = prctl(PR_GET_KEEPCAPS, 0, 0, 0, 0)) < 0)
perr("Couldn't get PR_SET_KEEPCAPS flag value");
else
printf("KEEPCAPS: %d\n", p);
printf("uid: %d, euid: %d, suid: %d\ngid: %d. egid: %d, sgid: %d\n", uid, euid, suid, gid, egid, sgid);
printf("Caps: %s\n", cap_to_text(caps, NULL));
cap_free(caps);
printf("*****\n\n");
}
/* drop_cap() permanently removes a capability from the permitted set. There is
* no way to recover the capability after this. You do not need to remove
* it from the effective set before calling this.
*/
void drop_cap(cap_value_t cap)
{
if (_stp_no_caps == 0) {
cap_t caps = cap_get_proc();
if (caps == NULL)
ferror("cap_get_proc failed");
if (cap_set_flag(caps, CAP_PERMITTED, 1, &cap, CAP_CLEAR) < 0)
ferror("Could not clear effective capabilities");
if (cap_set_proc(caps) < 0)
ferror("Could not apply capability set");
cap_free(caps);
}
}
/* add_cap() adds a permitted capability to the effective set. */
void add_cap(cap_value_t cap)
{
if (_stp_no_caps == 0) {
cap_t caps = cap_get_proc();
if (caps == NULL)
ferror("cap_get_proc failed");
if (cap_set_flag(caps, CAP_EFFECTIVE, 1, &cap, CAP_SET) < 0)
ferror("Could not set effective capabilities");
if (cap_set_proc(caps) < 0)
ferror("Could not apply capability set");
cap_free(caps);
}
}
/* del_cap() deletes a permitted capability from the effective set. */
void del_cap(cap_value_t cap)
{
if (_stp_no_caps == 0) {
cap_t caps = cap_get_proc();
if (caps == NULL)
ferror("cap_get_proc failed");
if (cap_set_flag(caps, CAP_EFFECTIVE, 1, &cap, CAP_CLEAR) < 0)
ferror("Could not clear effective capabilities");
if (cap_set_proc(caps) < 0)
ferror("Could not apply capability set");
cap_free(caps);
}
}
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