[lttng-tools.git] / librunas / 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 <lttngerr.h>

/*
 * We allocate a stack of twice this size and point in the middle of it
 * to support archs with stack growing up and down.
 */
#define CHILD_STACK_SIZE 2048

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

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

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

/*
 * Create recursively directory using the FULL path.
 */
static
int _mkdir_recursive(void *_data)
{
	struct 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 mkdir_data *data = _data;
	return mkdir(data->path, data->mode);
}

static
int _open(void *_data)
{
	struct 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.
	 */
	ret = setegid(data->gid);
	if (ret < 0) {
		perror("setegid");
		exit(EXIT_FAILURE);
	}
	ret = seteuid(data->uid);
	if (ret < 0) {
		perror("seteuid");
		exit(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");
			exit(EXIT_FAILURE);
		}
		writeleft -= writelen;
		index += writelen;
	} while (writeleft > 0);

	exit(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;
	char *child_stack;
	int retval_pipe[2];
	ssize_t readlen, readleft, index;
	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;
		}
	}

	child_stack = malloc(CHILD_STACK_SIZE * 2);
	if (!child_stack) {
		return -ENOMEM;
	}
	ret = pipe(retval_pipe);
	if (ret < 0) {
		perror("pipe");
		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 */

	pid = clone(child_run_as, child_stack + CHILD_STACK_SIZE,
		CLONE_FILES | SIGCHLD, &run_as_data, NULL);
	if (pid < 0) {
		perror("clone");
		ret = pid;
		goto close_pipe;
	}
	/* 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 = wait(&status);
	if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
		perror("wait");
		ret = -1;
	}
close_pipe:
	close(retval_pipe[0]);
	close(retval_pipe[1]);
end:
	free(child_stack);
	return retval.i;
}

int mkdir_recursive_run_as(const char *path, mode_t mode, uid_t uid, gid_t gid)
{
	struct 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 mkdir_run_as(const char *path, mode_t mode, uid_t uid, gid_t gid)
{
	struct 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 open_run_as(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
{
	struct open_data data;

	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>
60b6c79c MD	31
	32	#include <lttngerr.h>
	33
c2b75c49 MD	34	/*
	35	* We allocate a stack of twice this size and point in the middle of it
	36	* to support archs with stack growing up and down.
	37	*/
	38	#define CHILD_STACK_SIZE 2048
	39
	40	struct run_as_data {
	41	int (cmd)(void data);
	42	void *data;
	43	uid_t uid;
	44	gid_t gid;
	45	int retval_pipe;
	46	};
	47
60b6c79c MD	48	struct mkdir_data {
	49	const char *path;
	50	mode_t mode;
	51	};
	52
	53	struct open_data {
	54	const char *path;
	55	int flags;
	56	mode_t mode;
	57	};
	58
	59	/*
	60	* Create recursively directory using the FULL path.
	61	*/
	62	static
	63	int _mkdir_recursive(void *_data)
	64	{
	65	struct mkdir_data *data = _data;
	66	const char *path;
	67	char *p, tmp[PATH_MAX];
	68	struct stat statbuf;
	69	mode_t mode;
	70	size_t len;
	71	int ret;
	72
	73	path = data->path;
	74	mode = data->mode;
	75
	76	ret = snprintf(tmp, sizeof(tmp), "%s", path);
	77	if (ret < 0) {
	78	PERROR("snprintf mkdir");
	79	goto error;
	80	}
	81
	82	len = ret;
	83	if (tmp[len - 1] == '/') {
	84	tmp[len - 1] = 0;
	85	}
	86
	87	for (p = tmp + 1; *p; p++) {
	88	if (*p == '/') {
	89	*p = 0;
	90	ret = stat(tmp, &statbuf);
	91	if (ret < 0) {
	92	ret = mkdir(tmp, mode);
	93	if (ret < 0) {
	94	if (!(errno == EEXIST)) {
	95	PERROR("mkdir recursive");
	96	ret = -errno;
	97	goto error;
	98	}
	99	}
	100	}
	101	*p = '/';
	102	}
	103	}
	104
	105	ret = mkdir(tmp, mode);
	106	if (ret < 0) {
	107	if (!(errno == EEXIST)) {
	108	PERROR("mkdir recursive last piece");
	109	ret = -errno;
	110	} else {
	111	ret = 0;
112	}
113	}
114
115	error:
116	return ret;
117	}
118
119	static
120	int _mkdir(void *_data)
121	{
122	struct mkdir_data *data = _data;
123	return mkdir(data->path, data->mode);
124	}
125
126	static
127	int _open(void *_data)
128	{
129	struct open_data *data = _data;
130	return open(data->path, data->flags, data->mode);
131	}
132
c2b75c49 MD	133	static
	134	int child_run_as(void *_data)
	135	{
	136	struct run_as_data *data = _data;
	137	size_t writelen, writeleft, index;
	138	union {
	139	int i;
	140	char c[sizeof(int)];
	141	} sendret;
	142	int ret;
	143
	144	/*
	145	* Child: it is safe to drop egid and euid while sharing the
	146	* file descriptors with the parent process, since we do not
	147	* drop "uid": therefore, the user we are dropping egid/euid to
	148	* cannot attach to this process with, e.g. ptrace, nor map this
	149	* process memory.
	150	*/
	151	ret = setegid(data->gid);
	152	if (ret < 0) {
	153	perror("setegid");
	154	exit(EXIT_FAILURE);
	155	}
	156	ret = seteuid(data->uid);
	157	if (ret < 0) {
	158	perror("seteuid");
	159	exit(EXIT_FAILURE);
	160	}
	161	/*
	162	* Also set umask to 0 for mkdir executable bit.
	163	*/
	164	umask(0);
	165	sendret.i = (*data->cmd)(data->data);
	166	/* send back return value */
	167	writeleft = sizeof(sendret);
	168	index = 0;
	169	do {
	170	writelen = write(data->retval_pipe, &sendret.c[index],
	171	writeleft);
	172	if (writelen < 0) {
	173	perror("write");
	174	exit(EXIT_FAILURE);
	175	}
	176	writeleft -= writelen;
	177	index += writelen;
	178	} while (writeleft > 0);
	179
	180	exit(EXIT_SUCCESS);
	181	}
	182
60b6c79c MD	183	static
	184	int run_as(int (cmd)(void data), void *data, uid_t uid, gid_t gid)
	185	{
c2b75c49	186	struct run_as_data run_as_data;
60b6c79c	187	int ret = 0;
c2b75c49	188	int status;
60b6c79c	189	pid_t pid;
c2b75c49 MD	190	char *child_stack;
	191	int retval_pipe[2];
	192	ssize_t readlen, readleft, index;
	193	union {
	194	int i;
	195	char c[sizeof(int)];
	196	} retval;
60b6c79c MD	197
	198	/*
	199	* If we are non-root, we can only deal with our own uid.
	200	*/
	201	if (geteuid() != 0) {
	202	if (uid != geteuid()) {
	203	ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
	204	uid, geteuid());
	205	return -EPERM;
	206	}
60b6c79c MD	207	}
60b6c79c MD	208
c2b75c49 MD	209	child_stack = malloc(CHILD_STACK_SIZE * 2);
	210	if (!child_stack) {
	211	return -ENOMEM;
	212	}
	213	ret = pipe(retval_pipe);
	214	if (ret < 0) {
	215	perror("pipe");
60b6c79c	216	goto end;
c2b75c49 MD	217	}
	218	run_as_data.data = data;
	219	run_as_data.cmd = cmd;
	220	run_as_data.uid = uid;
	221	run_as_data.gid = gid;
	222	run_as_data.retval_pipe = retval_pipe[1]; /* write end */
	223
	224	pid = clone(child_run_as, child_stack + CHILD_STACK_SIZE,
	225	CLONE_FILES \| SIGCHLD, &run_as_data, NULL);
	226	if (pid < 0) {
	227	perror("clone");
	228	ret = pid;
	229	goto close_pipe;
	230	}
	231	/* receive return value */
	232	readleft = sizeof(retval);
	233	index = 0;
	234	do {
	235	readlen = read(retval_pipe[0], &retval.c[index], readleft);
	236	if (readlen < 0) {
	237	perror("read");
	238	ret = -1;
	239	break;
60b6c79c	240	}
c2b75c49 MD	241	readleft -= readlen;
	242	index += readlen;
	243	} while (readleft > 0);
	244
	245	/*
	246	* Parent: wait for child to return, in which case the
	247	* shared memory map will have been created.
	248	*/
	249	pid = wait(&status);
	250	if (pid < 0 \|\| !WIFEXITED(status) \|\| WEXITSTATUS(status) != 0) {
	251	perror("wait");
	252	ret = -1;
60b6c79c	253	}
c2b75c49 MD	254	close_pipe:
	255	close(retval_pipe[0]);
	256	close(retval_pipe[1]);
60b6c79c	257	end:
c2b75c49 MD	258	free(child_stack);
c2b75c49 MD	259	return retval.i;
60b6c79c MD	260	}
	261
	262	int mkdir_recursive_run_as(const char *path, mode_t mode, uid_t uid, gid_t gid)
	263	{
	264	struct mkdir_data data;
	265
	266	DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
	267	path, mode, uid, gid);
	268	data.path = path;
	269	data.mode = mode;
	270	return run_as(_mkdir_recursive, &data, uid, gid);
	271	}
	272
	273	int mkdir_run_as(const char *path, mode_t mode, uid_t uid, gid_t gid)
	274	{
	275	struct mkdir_data data;
	276
	277	DBG3("mkdir() %s with mode %d for uid %d and gid %d",
	278	path, mode, uid, gid);
	279	data.path = path;
	280	data.mode = mode;
	281	return run_as(_mkdir, &data, uid, gid);
	282	}
	283
	284	/*
	285	* Note: open_run_as is currently not working. We'd need to pass the fd
	286	* opened in the child to the parent.
	287	*/
	288	int open_run_as(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
	289	{
c2b75c49 MD	290	struct open_data data;
c2b75c49 MD	291
60b6c79c MD	292	data.path = path;
	293	data.flags = flags;
	294	data.mode = mode;
	295	return run_as(_open, &data, uid, gid);
60b6c79c	296	}