rootwrap.c 6.7 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
/*****************************************************************************
 * rootwrap.c
 *****************************************************************************
 * Copyright © 2005-2008 Rémi Denis-Courmont
 *
 * 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., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
 *****************************************************************************/

#if HAVE_CONFIG_H
# include <config.h>
#endif
24
#define _XPG4_2 /* ancilliary data on Solaris */
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48

#include <stdlib.h> /* exit() */
#include <stdio.h>
#include <string.h>

#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <sys/resource.h> /* getrlimit() */
#include <sched.h>
#include <errno.h>
#include <netinet/in.h>

#if defined (AF_INET6) && !defined (IPV6_V6ONLY)
# warning Uho, your IPv6 support is broken and has been disabled. Fix your C library.
# undef AF_INET6
#endif

#ifndef AF_LOCAL
# define AF_LOCAL AF_UNIX
#endif
49
50
51
52
53
54
55
56
57
58
/* Required yet non-standard cmsg functions */
#ifndef CMSG_ALIGN
# define CMSG_ALIGN(len) (((len) + sizeof(intptr_t)-1) & ~(sizeof(intptr_t)-1))
#endif
#ifndef CMSG_SPACE
# define CMSG_SPACE(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + CMSG_ALIGN(len))
#endif
#ifndef CMSG_LEN
# define CMSG_LEN(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + (len))
#endif
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108

static inline int is_allowed_port (uint16_t port)
{
    port = ntohs (port);
    return (port == 80) || (port == 443) || (port == 554);
}


static inline int send_err (int fd, int err)
{
    return send (fd, &err, sizeof (err), 0) == sizeof (err) ? 0 : -1;
}

/**
 * Send a file descriptor to another process
 */
static int send_fd (int p, int fd)
{
    struct msghdr hdr;
    struct iovec iov;
    struct cmsghdr *cmsg;
    char buf[CMSG_SPACE (sizeof (fd))];
    int val = 0;

    hdr.msg_name = NULL;
    hdr.msg_namelen = 0;
    hdr.msg_iov = &iov;
    hdr.msg_iovlen = 1;
    hdr.msg_control = buf;
    hdr.msg_controllen = sizeof (buf);

    iov.iov_base = &val;
    iov.iov_len = sizeof (val);

    cmsg = CMSG_FIRSTHDR (&hdr);
    cmsg->cmsg_level = SOL_SOCKET;
    cmsg->cmsg_type = SCM_RIGHTS;
    cmsg->cmsg_len = CMSG_LEN (sizeof (fd));
    memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
    hdr.msg_controllen = cmsg->cmsg_len;

    return sendmsg (p, &hdr, 0) == sizeof (val) ? 0 : -1;
}


/**
 * Background process run as root to open privileged TCP ports.
 */
static void rootprocess (int fd)
{
109
110
111
112
113
114
115
116
117
    union
    {
        struct sockaddr         sa;
        struct sockaddr_storage ss;
        struct sockaddr_in      sin;
#ifdef AF_INET6
        struct sockaddr_in6     sin6;
#endif
    } addr;
118

119
    while (recv (fd, &addr.ss, sizeof (addr.ss), 0) == sizeof (addr.ss))
120
121
122
    {
        unsigned len;
        int sock;
123
        int family;
124

125
        switch (addr.sa.sa_family)
126
127
        {
            case AF_INET:
128
                if (!is_allowed_port (addr.sin.sin_port))
129
130
131
132
133
134
                {
                    if (send_err (fd, EACCES))
                        return;
                    continue;
                }
                len = sizeof (struct sockaddr_in);
135
                family = PF_INET;
136
137
138
139
                break;

#ifdef AF_INET6
            case AF_INET6:
140
                if (!is_allowed_port (addr.sin6.sin6_port))
141
142
143
144
145
146
                {
                    if (send_err (fd, EACCES))
                        return;
                    continue;
                }
                len = sizeof (struct sockaddr_in6);
147
                family = PF_INET6;
148
149
150
151
152
153
154
155
156
                break;
#endif

            default:
                if (send_err (fd, EAFNOSUPPORT))
                    return;
                continue;
        }

157
        sock = socket (family, SOCK_STREAM, IPPROTO_TCP);
158
159
160
161
162
163
        if (sock != -1)
        {
            const int val = 1;

            setsockopt (sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof (val));
#ifdef AF_INET6
164
            if (addr.sa.sa_family == AF_INET6)
165
166
                setsockopt (sock, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof (val));
#endif
167
            if (bind (sock, &addr.sa, len) == 0)
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
            {
                send_fd (fd, sock);
                close (sock);
                continue;
            }
        }
        send_err (fd, errno);
    }
}

/* TODO?
 *  - use libcap if available,
 *  - call chroot
 */

int main (int argc, char *argv[])
{
    /* Support for dynamically opening RTSP, HTTP and HTTP/SSL ports */
    int pair[2];

    if (socketpair (AF_LOCAL, SOCK_STREAM, 0, pair))
        return 1;
    if (pair[0] < 3)
        goto error; /* we want 0, 1 and 2 open */

    pid_t pid = fork ();
    switch (pid)
    {
        case -1:
            goto error;

        case 0:
        {
            int null = open ("/dev/null", O_RDWR);
            if (null != -1)
            {
                dup2 (null, 0);
                dup2 (null, 1);
                dup2 (null, 2);
                close (null);
            }
            close (pair[0]);
            setsid ();
            rootprocess (pair[1]);
            exit (0);
        }
    }

    close (pair[1]);
    pair[1] = -1;

    char buf[21];
    snprintf (buf, sizeof (buf), "%d", pair[0]);
    setenv ("VLC_ROOTWRAP_SOCK", buf, 1);

    /* Support for real-time priorities */
#ifdef RLIMIT_RTPRIO
    struct rlimit rlim;
    rlim.rlim_max = rlim.rlim_cur = sched_get_priority_min (SCHED_RR) + 24;
    setrlimit (RLIMIT_RTPRIO, &rlim);
#endif

    uid_t uid = getuid ();
    if (uid == 0)
    {
        const char *sudo = getenv ("SUDO_UID");
        if (sudo)
            uid = atoi (sudo);
    }
    if (uid == 0)
    {
        fprintf (stderr, "Cannot determine unprivileged user for VLC!\n");
        exit (1);
    }
    setuid (uid);

    if (!setuid (0)) /* sanity check: we cannot get root back */
        exit (1);

    /* Yeah, the user can execute just about anything from here.
     * But we've dropped privileges, so it does not matter. */
    if (strlen (argv[0]) < sizeof ("-wrapper"))
        goto error;
    argv[0][strlen (argv[0]) - strlen ("-wrapper")] = '\0';

    (void)argc;
    if (execvp (argv[0], argv))
        perror (argv[0]);

error:
    close (pair[0]);
    if (pair[1] != -1)
        close (pair[1]);
    return 1;
}