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

#include "runas.h"

#define RUNAS_CHILD_STACK_SIZE	10485760

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");
		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");
		ret = -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");
		ret = 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");
		ret = -1;
	}
unmap_stack:
	ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
	if (ret < 0) {
		perror("munmap");
	}
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>
d5bd7573	31	#include <sys/mman.h>
60b6c79c MD	32
	33	#include <lttngerr.h>
	34
0857097f DG	35	#include "runas.h"
0857097f DG	36
e11d277b	37	#define RUNAS_CHILD_STACK_SIZE 10485760
c2b75c49 MD	38
	39	struct run_as_data {
	40	int (cmd)(void data);
	41	void *data;
	42	uid_t uid;
	43	gid_t gid;
	44	int retval_pipe;
	45	};
	46
e11d277b	47	struct run_as_mkdir_data {
60b6c79c MD	48	const char *path;
	49	mode_t mode;
	50	};
	51
e11d277b	52	struct run_as_open_data {
60b6c79c MD	53	const char *path;
	54	int flags;
	55	mode_t mode;
	56	};
	57
	58	/*
	59	* Create recursively directory using the FULL path.
	60	*/
	61	static
	62	int _mkdir_recursive(void *_data)
	63	{
e11d277b	64	struct run_as_mkdir_data *data = _data;
60b6c79c MD	65	const char *path;
	66	char *p, tmp[PATH_MAX];
	67	struct stat statbuf;
	68	mode_t mode;
	69	size_t len;
	70	int ret;
	71
	72	path = data->path;
	73	mode = data->mode;
	74
	75	ret = snprintf(tmp, sizeof(tmp), "%s", path);
	76	if (ret < 0) {
	77	PERROR("snprintf mkdir");
	78	goto error;
	79	}
	80
	81	len = ret;
	82	if (tmp[len - 1] == '/') {
	83	tmp[len - 1] = 0;
	84	}
	85
	86	for (p = tmp + 1; *p; p++) {
	87	if (*p == '/') {
	88	*p = 0;
	89	ret = stat(tmp, &statbuf);
	90	if (ret < 0) {
	91	ret = mkdir(tmp, mode);
	92	if (ret < 0) {
	93	if (!(errno == EEXIST)) {
	94	PERROR("mkdir recursive");
	95	ret = -errno;
	96	goto error;
	97	}
	98	}
	99	}
	100	*p = '/';
	101	}
	102	}
	103
	104	ret = mkdir(tmp, mode);
	105	if (ret < 0) {
	106	if (!(errno == EEXIST)) {
	107	PERROR("mkdir recursive last piece");
	108	ret = -errno;
	109	} else {
	110	ret = 0;
	111	}
	112	}
	113
	114	error:
	115	return ret;
	116	}
	117
	118	static
	119	int _mkdir(void *_data)
	120	{
e11d277b	121	struct run_as_mkdir_data *data = _data;
60b6c79c MD	122	return mkdir(data->path, data->mode);
	123	}
	124
	125	static
	126	int _open(void *_data)
	127	{
e11d277b	128	struct run_as_open_data *data = _data;
60b6c79c MD	129	return open(data->path, data->flags, data->mode);
	130	}
	131
c2b75c49 MD	132	static
	133	int child_run_as(void *_data)
	134	{
	135	struct run_as_data *data = _data;
	136	size_t writelen, writeleft, index;
	137	union {
	138	int i;
	139	char c[sizeof(int)];
	140	} sendret;
	141	int ret;
	142
	143	/*
	144	* Child: it is safe to drop egid and euid while sharing the
	145	* file descriptors with the parent process, since we do not
	146	* drop "uid": therefore, the user we are dropping egid/euid to
	147	* cannot attach to this process with, e.g. ptrace, nor map this
	148	* process memory.
	149	*/
1576d582 MD	150	if (data->gid != getegid()) {
	151	ret = setegid(data->gid);
	152	if (ret < 0) {
	153	perror("setegid");
6da9f915	154	return EXIT_FAILURE;
1576d582	155	}
c2b75c49	156	}
1576d582 MD	157	if (data->uid != geteuid()) {
	158	ret = seteuid(data->uid);
	159	if (ret < 0) {
	160	perror("seteuid");
6da9f915	161	return EXIT_FAILURE;
1576d582	162	}
c2b75c49 MD	163	}
	164	/*
	165	* Also set umask to 0 for mkdir executable bit.
	166	*/
	167	umask(0);
	168	sendret.i = (*data->cmd)(data->data);
	169	/* send back return value */
	170	writeleft = sizeof(sendret);
	171	index = 0;
	172	do {
	173	writelen = write(data->retval_pipe, &sendret.c[index],
	174	writeleft);
	175	if (writelen < 0) {
	176	perror("write");
6da9f915	177	return EXIT_FAILURE;
c2b75c49 MD	178	}
	179	writeleft -= writelen;
	180	index += writelen;
	181	} while (writeleft > 0);
6da9f915	182	return EXIT_SUCCESS;
c2b75c49 MD	183	}
c2b75c49 MD	184
60b6c79c MD	185	static
	186	int run_as(int (cmd)(void data), void *data, uid_t uid, gid_t gid)
	187	{
c2b75c49	188	struct run_as_data run_as_data;
60b6c79c	189	int ret = 0;
c2b75c49	190	int status;
60b6c79c	191	pid_t pid;
c2b75c49 MD	192	int retval_pipe[2];
c2b75c49 MD	193	ssize_t readlen, readleft, index;
d5bd7573	194	void *child_stack;
c2b75c49 MD	195	union {
	196	int i;
	197	char c[sizeof(int)];
	198	} retval;
60b6c79c MD	199
	200	/*
	201	* If we are non-root, we can only deal with our own uid.
	202	*/
	203	if (geteuid() != 0) {
	204	if (uid != geteuid()) {
	205	ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
	206	uid, geteuid());
	207	return -EPERM;
	208	}
60b6c79c MD	209	}
60b6c79c MD	210
c2b75c49 MD	211	ret = pipe(retval_pipe);
	212	if (ret < 0) {
	213	perror("pipe");
60b6c79c	214	goto end;
c2b75c49 MD	215	}
	216	run_as_data.data = data;
	217	run_as_data.cmd = cmd;
	218	run_as_data.uid = uid;
	219	run_as_data.gid = gid;
	220	run_as_data.retval_pipe = retval_pipe[1]; /* write end */
e11d277b	221	child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
d5bd7573 MD	222	PROT_WRITE \| PROT_READ,
	223	MAP_PRIVATE \| MAP_GROWSDOWN \| MAP_ANONYMOUS \| MAP_STACK,
	224	-1, 0);
	225	if (child_stack == MAP_FAILED) {
	226	perror("mmap");
	227	ret = -ENOMEM;
	228	goto close_pipe;
	229	}
	230	/*
	231	* Pointing to the middle of the stack to support architectures
	232	* where the stack grows up (HPPA).
	233	*/
e11d277b	234	pid = clone(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
9beed4cb	235	CLONE_FILES \| SIGCHLD,
d5bd7573	236	&run_as_data, NULL);
c2b75c49 MD	237	if (pid < 0) {
	238	perror("clone");
	239	ret = pid;
d5bd7573	240	goto unmap_stack;
c2b75c49 MD	241	}
	242	/* receive return value */
	243	readleft = sizeof(retval);
	244	index = 0;
	245	do {
	246	readlen = read(retval_pipe[0], &retval.c[index], readleft);
	247	if (readlen < 0) {
	248	perror("read");
	249	ret = -1;
	250	break;
60b6c79c	251	}
c2b75c49 MD	252	readleft -= readlen;
	253	index += readlen;
	254	} while (readleft > 0);
	255
	256	/*
	257	* Parent: wait for child to return, in which case the
	258	* shared memory map will have been created.
	259	*/
47fb7563	260	pid = waitpid(pid, &status, 0);
c2b75c49 MD	261	if (pid < 0 \|\| !WIFEXITED(status) \|\| WEXITSTATUS(status) != 0) {
	262	perror("wait");
	263	ret = -1;
60b6c79c	264	}
d5bd7573	265	unmap_stack:
e11d277b	266	ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
d5bd7573 MD	267	if (ret < 0) {
	268	perror("munmap");
	269	}
c2b75c49 MD	270	close_pipe:
	271	close(retval_pipe[0]);
	272	close(retval_pipe[1]);
60b6c79c	273	end:
c2b75c49	274	return retval.i;
60b6c79c MD	275	}
60b6c79c MD	276
e11d277b	277	int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
60b6c79c	278	{
e11d277b	279	struct run_as_mkdir_data data;
60b6c79c MD	280
	281	DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
	282	path, mode, uid, gid);
	283	data.path = path;
	284	data.mode = mode;
	285	return run_as(_mkdir_recursive, &data, uid, gid);
	286	}
	287
e11d277b	288	int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
60b6c79c	289	{
e11d277b	290	struct run_as_mkdir_data data;
60b6c79c MD	291
	292	DBG3("mkdir() %s with mode %d for uid %d and gid %d",
	293	path, mode, uid, gid);
	294	data.path = path;
	295	data.mode = mode;
	296	return run_as(_mkdir, &data, uid, gid);
	297	}
	298
	299	/*
	300	* Note: open_run_as is currently not working. We'd need to pass the fd
	301	* opened in the child to the parent.
	302	*/
e11d277b	303	int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
60b6c79c	304	{
e11d277b	305	struct run_as_open_data data;
c2b75c49	306
47fb7563 MD	307	DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
47fb7563 MD	308	path, flags, mode, uid, gid);
60b6c79c MD	309	data.path = path;
	310	data.flags = flags;
	311	data.mode = mode;
	312	return run_as(_open, &data, uid, gid);
60b6c79c	313	}