[lttng-tools.git] / src / common / runas.c

/*
 * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
 *                      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * 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; only version 2 of the License.
 *
 * 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.
 */

#define _GNU_SOURCE
#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sched.h>
#include <sys/mman.h>

#include <common/error.h>

#include "runas.h"

#define RUNAS_CHILD_STACK_SIZE	10485760

#ifndef MAP_STACK
#define MAP_STACK		0
#endif

struct run_as_data {
	int (*cmd)(void *data);
	void *data;
	uid_t uid;
	gid_t gid;
	int retval_pipe;
};

struct run_as_mkdir_data {
	const char *path;
	mode_t mode;
};

struct run_as_open_data {
	const char *path;
	int flags;
	mode_t mode;
};

/*
 * Create recursively directory using the FULL path.
 */
static
int _mkdir_recursive(void *_data)
{
	struct run_as_mkdir_data *data = _data;
	const char *path;
	char *p, tmp[PATH_MAX];
	struct stat statbuf;
	mode_t mode;
	size_t len;
	int ret;

	path = data->path;
	mode = data->mode;

	ret = snprintf(tmp, sizeof(tmp), "%s", path);
	if (ret < 0) {
		PERROR("snprintf mkdir");
		goto error;
	}

	len = ret;
	if (tmp[len - 1] == '/') {
		tmp[len - 1] = 0;
	}

	for (p = tmp + 1; *p; p++) {
		if (*p == '/') {
			*p = 0;
			ret = stat(tmp, &statbuf);
			if (ret < 0) {
				ret = mkdir(tmp, mode);
				if (ret < 0) {
					if (!(errno == EEXIST)) {
						PERROR("mkdir recursive");
						ret = -errno;
						goto error;
					}
				}
			}
			*p = '/';
		}
	}

	ret = mkdir(tmp, mode);
	if (ret < 0) {
		if (!(errno == EEXIST)) {
			PERROR("mkdir recursive last piece");
			ret = -errno;
		} else {
			ret = 0;
		}
	}

error:
	return ret;
}

static
int _mkdir(void *_data)
{
	struct run_as_mkdir_data *data = _data;
	return mkdir(data->path, data->mode);
}

static
int _open(void *_data)
{
	struct run_as_open_data *data = _data;
	return open(data->path, data->flags, data->mode);
}

static
int child_run_as(void *_data)
{
	struct run_as_data *data = _data;
	size_t writelen, writeleft, index;
	union {
		int i;
		char c[sizeof(int)];
	} sendret;
	int ret;

	/*
	 * Child: it is safe to drop egid and euid while sharing the
	 * file descriptors with the parent process, since we do not
	 * drop "uid": therefore, the user we are dropping egid/euid to
	 * cannot attach to this process with, e.g. ptrace, nor map this
	 * process memory.
	 */
	if (data->gid != getegid()) {
		ret = setegid(data->gid);
		if (ret < 0) {
			perror("setegid");
			return EXIT_FAILURE;
		}
	}
	if (data->uid != geteuid()) {
		ret = seteuid(data->uid);
		if (ret < 0) {
			perror("seteuid");
			return EXIT_FAILURE;
		}
	}
	/*
	 * Also set umask to 0 for mkdir executable bit.
	 */
	umask(0);
	sendret.i = (*data->cmd)(data->data);
	/* send back return value */
	writeleft = sizeof(sendret);
	index = 0;
	do {
		writelen = write(data->retval_pipe, &sendret.c[index],
				writeleft);
		if (writelen < 0) {
			perror("write");
			return EXIT_FAILURE;
		}
		writeleft -= writelen;
		index += writelen;
	} while (writeleft > 0);
	return EXIT_SUCCESS;
}

static
int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
{
	struct run_as_data run_as_data;
	int ret = 0;
	int status;
	pid_t pid;
	int retval_pipe[2];
	ssize_t readlen, readleft, index;
	void *child_stack;
	union {
		int i;
		char c[sizeof(int)];
	} retval;

	/*
	 * If we are non-root, we can only deal with our own uid.
	 */
	if (geteuid() != 0) {
		if (uid != geteuid()) {
			ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
				uid, geteuid());
			return -EPERM;
		}
	}

	ret = pipe(retval_pipe);
	if (ret < 0) {
		perror("pipe");
		retval.i = ret;
		goto end;
	}
	run_as_data.data = data;
	run_as_data.cmd = cmd;
	run_as_data.uid = uid;
	run_as_data.gid = gid;
	run_as_data.retval_pipe = retval_pipe[1];	/* write end */
	child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
		PROT_WRITE | PROT_READ,
		MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | MAP_STACK,
		-1, 0);
	if (child_stack == MAP_FAILED) {
		perror("mmap");
		retval.i = -ENOMEM;
		goto close_pipe;
	}
	/*
	 * Pointing to the middle of the stack to support architectures
	 * where the stack grows up (HPPA).
	 */
	pid = clone(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
		CLONE_FILES | SIGCHLD,
		&run_as_data, NULL);
	if (pid < 0) {
		perror("clone");
		retval.i = pid;
		goto unmap_stack;
	}
	/* receive return value */
	readleft = sizeof(retval);
	index = 0;
	do {
		readlen = read(retval_pipe[0], &retval.c[index], readleft);
		if (readlen < 0) {
			perror("read");
			ret = -1;
			break;
		}
		readleft -= readlen;
		index += readlen;
	} while (readleft > 0);

	/*
	 * Parent: wait for child to return, in which case the
	 * shared memory map will have been created.
	 */
	pid = waitpid(pid, &status, 0);
	if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
		perror("wait");
		retval.i = -1;
	}
unmap_stack:
	ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
	if (ret < 0) {
		perror("munmap");
		retval.i = ret;
	}
close_pipe:
	close(retval_pipe[0]);
	close(retval_pipe[1]);
end:
	return retval.i;
}

int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
{
	struct run_as_mkdir_data data;

	DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
			path, mode, uid, gid);
	data.path = path;
	data.mode = mode;
	return run_as(_mkdir_recursive, &data, uid, gid);
}

int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
{
	struct run_as_mkdir_data data;

	DBG3("mkdir() %s with mode %d for uid %d and gid %d",
			path, mode, uid, gid);
	data.path = path;
	data.mode = mode;
	return run_as(_mkdir, &data, uid, gid);
}

/*
 * Note: open_run_as is currently not working. We'd need to pass the fd
 * opened in the child to the parent.
 */
int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
{
	struct run_as_open_data data;

	DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
			path, flags, mode, uid, gid);
	data.path = path;
	data.flags = flags;
	data.mode = mode;
	return run_as(_open, &data, uid, gid);
}
Commit	Line	Data
60b6c79c MD	1	/*
	2	* Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
	3	* Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	4	*
	5	* This program is free software; you can redistribute it and/or modify it
	6	* under the terms of the GNU General Public License as published by the Free
	7	* Software Foundation; only version 2 of the License.
	8	*
	9	* This program is distributed in the hope that it will be useful, but WITHOUT
	10	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	11	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
	12	* more details.
	13	*
	14	* You should have received a copy of the GNU General Public License along with
	15	* this program; if not, write to the Free Software Foundation, Inc., 59 Temple
	16	* Place - Suite 330, Boston, MA 02111-1307, USA.
	17	*/
	18
	19	#define _GNU_SOURCE
	20	#include <errno.h>
	21	#include <limits.h>
	22	#include <stdio.h>
	23	#include <stdlib.h>
	24	#include <string.h>
	25	#include <sys/wait.h>
	26	#include <sys/types.h>
	27	#include <sys/stat.h>
	28	#include <unistd.h>
	29	#include <fcntl.h>
c2b75c49	30	#include <sched.h>
ca4537d3	31	#include <sys/mman.h>
60b6c79c	32
db758600	33	#include <common/error.h>
60b6c79c	34
0857097f DG	35	#include "runas.h"
0857097f DG	36
e11d277b	37	#define RUNAS_CHILD_STACK_SIZE 10485760
c2b75c49	38
059e1d3d MD	39	#ifndef MAP_STACK
	40	#define MAP_STACK 0
	41	#endif
	42
c2b75c49 MD	43	struct run_as_data {
	44	int (cmd)(void data);
	45	void *data;
	46	uid_t uid;
	47	gid_t gid;
	48	int retval_pipe;
	49	};
	50
e11d277b	51	struct run_as_mkdir_data {
60b6c79c MD	52	const char *path;
	53	mode_t mode;
	54	};
	55
e11d277b	56	struct run_as_open_data {
60b6c79c MD	57	const char *path;
	58	int flags;
	59	mode_t mode;
	60	};
	61
	62	/*
	63	* Create recursively directory using the FULL path.
	64	*/
	65	static
	66	int _mkdir_recursive(void *_data)
	67	{
e11d277b	68	struct run_as_mkdir_data *data = _data;
60b6c79c MD	69	const char *path;
	70	char *p, tmp[PATH_MAX];
	71	struct stat statbuf;
	72	mode_t mode;
	73	size_t len;
	74	int ret;
	75
	76	path = data->path;
	77	mode = data->mode;
	78
	79	ret = snprintf(tmp, sizeof(tmp), "%s", path);
	80	if (ret < 0) {
	81	PERROR("snprintf mkdir");
	82	goto error;
	83	}
	84
	85	len = ret;
	86	if (tmp[len - 1] == '/') {
	87	tmp[len - 1] = 0;
	88	}
	89
	90	for (p = tmp + 1; *p; p++) {
	91	if (*p == '/') {
	92	*p = 0;
	93	ret = stat(tmp, &statbuf);
	94	if (ret < 0) {
	95	ret = mkdir(tmp, mode);
	96	if (ret < 0) {
	97	if (!(errno == EEXIST)) {
	98	PERROR("mkdir recursive");
	99	ret = -errno;
	100	goto error;
	101	}
	102	}
	103	}
	104	*p = '/';
	105	}
	106	}
	107
	108	ret = mkdir(tmp, mode);
	109	if (ret < 0) {
	110	if (!(errno == EEXIST)) {
	111	PERROR("mkdir recursive last piece");
	112	ret = -errno;
	113	} else {
	114	ret = 0;
	115	}
	116	}
	117
	118	error:
	119	return ret;
	120	}
	121
	122	static
	123	int _mkdir(void *_data)
	124	{
e11d277b	125	struct run_as_mkdir_data *data = _data;
60b6c79c MD	126	return mkdir(data->path, data->mode);
	127	}
	128
	129	static
	130	int _open(void *_data)
	131	{
e11d277b	132	struct run_as_open_data *data = _data;
60b6c79c MD	133	return open(data->path, data->flags, data->mode);
	134	}
	135
c2b75c49 MD	136	static
	137	int child_run_as(void *_data)
	138	{
	139	struct run_as_data *data = _data;
	140	size_t writelen, writeleft, index;
	141	union {
	142	int i;
	143	char c[sizeof(int)];
	144	} sendret;
	145	int ret;
	146
	147	/*
	148	* Child: it is safe to drop egid and euid while sharing the
	149	* file descriptors with the parent process, since we do not
	150	* drop "uid": therefore, the user we are dropping egid/euid to
	151	* cannot attach to this process with, e.g. ptrace, nor map this
	152	* process memory.
	153	*/
1576d582 MD	154	if (data->gid != getegid()) {
	155	ret = setegid(data->gid);
	156	if (ret < 0) {
	157	perror("setegid");
6da9f915	158	return EXIT_FAILURE;
1576d582	159	}
c2b75c49	160	}
1576d582 MD	161	if (data->uid != geteuid()) {
	162	ret = seteuid(data->uid);
	163	if (ret < 0) {
	164	perror("seteuid");
6da9f915	165	return EXIT_FAILURE;
1576d582	166	}
c2b75c49 MD	167	}
	168	/*
	169	* Also set umask to 0 for mkdir executable bit.
	170	*/
	171	umask(0);
	172	sendret.i = (*data->cmd)(data->data);
	173	/* send back return value */
	174	writeleft = sizeof(sendret);
	175	index = 0;
	176	do {
	177	writelen = write(data->retval_pipe, &sendret.c[index],
	178	writeleft);
	179	if (writelen < 0) {
	180	perror("write");
6da9f915	181	return EXIT_FAILURE;
c2b75c49 MD	182	}
	183	writeleft -= writelen;
	184	index += writelen;
	185	} while (writeleft > 0);
6da9f915	186	return EXIT_SUCCESS;
c2b75c49 MD	187	}
c2b75c49 MD	188
60b6c79c MD	189	static
	190	int run_as(int (cmd)(void data), void *data, uid_t uid, gid_t gid)
	191	{
c2b75c49	192	struct run_as_data run_as_data;
60b6c79c	193	int ret = 0;
c2b75c49	194	int status;
60b6c79c	195	pid_t pid;
c2b75c49 MD	196	int retval_pipe[2];
c2b75c49 MD	197	ssize_t readlen, readleft, index;
d5bd7573	198	void *child_stack;
c2b75c49 MD	199	union {
	200	int i;
	201	char c[sizeof(int)];
	202	} retval;
60b6c79c MD	203
	204	/*
	205	* If we are non-root, we can only deal with our own uid.
	206	*/
	207	if (geteuid() != 0) {
	208	if (uid != geteuid()) {
	209	ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
	210	uid, geteuid());
	211	return -EPERM;
	212	}
60b6c79c MD	213	}
60b6c79c MD	214
c2b75c49 MD	215	ret = pipe(retval_pipe);
	216	if (ret < 0) {
	217	perror("pipe");
90755f8b	218	retval.i = ret;
60b6c79c	219	goto end;
c2b75c49 MD	220	}
	221	run_as_data.data = data;
	222	run_as_data.cmd = cmd;
	223	run_as_data.uid = uid;
	224	run_as_data.gid = gid;
	225	run_as_data.retval_pipe = retval_pipe[1]; /* write end */
e11d277b	226	child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
d5bd7573 MD	227	PROT_WRITE \| PROT_READ,
	228	MAP_PRIVATE \| MAP_GROWSDOWN \| MAP_ANONYMOUS \| MAP_STACK,
	229	-1, 0);
	230	if (child_stack == MAP_FAILED) {
	231	perror("mmap");
90755f8b	232	retval.i = -ENOMEM;
d5bd7573 MD	233	goto close_pipe;
	234	}
	235	/*
	236	* Pointing to the middle of the stack to support architectures
	237	* where the stack grows up (HPPA).
	238	*/
e11d277b	239	pid = clone(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
9beed4cb	240	CLONE_FILES \| SIGCHLD,
d5bd7573	241	&run_as_data, NULL);
c2b75c49 MD	242	if (pid < 0) {
c2b75c49 MD	243	perror("clone");
90755f8b	244	retval.i = pid;
d5bd7573	245	goto unmap_stack;
c2b75c49 MD	246	}
	247	/* receive return value */
	248	readleft = sizeof(retval);
	249	index = 0;
	250	do {
	251	readlen = read(retval_pipe[0], &retval.c[index], readleft);
	252	if (readlen < 0) {
	253	perror("read");
	254	ret = -1;
	255	break;
60b6c79c	256	}
c2b75c49 MD	257	readleft -= readlen;
	258	index += readlen;
	259	} while (readleft > 0);
	260
	261	/*
	262	* Parent: wait for child to return, in which case the
	263	* shared memory map will have been created.
	264	*/
47fb7563	265	pid = waitpid(pid, &status, 0);
c2b75c49 MD	266	if (pid < 0 \|\| !WIFEXITED(status) \|\| WEXITSTATUS(status) != 0) {
c2b75c49 MD	267	perror("wait");
90755f8b	268	retval.i = -1;
60b6c79c	269	}
d5bd7573	270	unmap_stack:
e11d277b	271	ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
d5bd7573 MD	272	if (ret < 0) {
d5bd7573 MD	273	perror("munmap");
90755f8b	274	retval.i = ret;
d5bd7573	275	}
c2b75c49 MD	276	close_pipe:
	277	close(retval_pipe[0]);
	278	close(retval_pipe[1]);
60b6c79c	279	end:
c2b75c49	280	return retval.i;
60b6c79c MD	281	}
60b6c79c MD	282
e11d277b	283	int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
60b6c79c	284	{
e11d277b	285	struct run_as_mkdir_data data;
60b6c79c MD	286
	287	DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
	288	path, mode, uid, gid);
	289	data.path = path;
	290	data.mode = mode;
	291	return run_as(_mkdir_recursive, &data, uid, gid);
	292	}
	293
e11d277b	294	int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
60b6c79c	295	{
e11d277b	296	struct run_as_mkdir_data data;
60b6c79c MD	297
	298	DBG3("mkdir() %s with mode %d for uid %d and gid %d",
	299	path, mode, uid, gid);
	300	data.path = path;
	301	data.mode = mode;
	302	return run_as(_mkdir, &data, uid, gid);
	303	}
	304
	305	/*
	306	* Note: open_run_as is currently not working. We'd need to pass the fd
	307	* opened in the child to the parent.
	308	*/
e11d277b	309	int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
60b6c79c	310	{
e11d277b	311	struct run_as_open_data data;
c2b75c49	312
47fb7563 MD	313	DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
47fb7563 MD	314	path, flags, mode, uid, gid);
60b6c79c MD	315	data.path = path;
	316	data.flags = flags;
	317	data.mode = mode;
	318	return run_as(_open, &data, uid, gid);
60b6c79c	319	}