src/nspawn/nspawn-setuid.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <fcntl.h>
   4 #include <sys/types.h>
   5 #include <unistd.h>
   6
   7 #include "alloc-util.h"
   8 #include "constants.h"
   9 #include "errno.h"
  10 #include "fd-util.h"
  11 #include "fileio.h"
  12 #include "mkdir.h"
  13 #include "nspawn-setuid.h"
  14 #include "process-util.h"
  15 #include "signal-util.h"
  16 #include "string-util.h"
  17 #include "strv.h"
  18 #include "user-util.h"
  19
  20 static int spawn_getent(const char *database, const char *key, pid_t *rpid) {
  21         int pipe_fds[2], r;
  22         pid_t pid;
  23
  24         assert(database);
  25         assert(key);
  26         assert(rpid);
  27
  28         if (pipe2(pipe_fds, O_CLOEXEC) < 0)
  29                 return log_error_errno(errno, "Failed to allocate pipe: %m");
  30
  31         r = safe_fork("(getent)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_LOG|FORK_RLIMIT_NOFILE_SAFE, &pid);
  32         if (r < 0) {
  33                 safe_close_pair(pipe_fds);
  34                 return r;
  35         }
  36         if (r == 0) {
  37                 char *empty_env = NULL;
  38
  39                 pipe_fds[0] = safe_close(pipe_fds[0]);
  40
  41                 if (rearrange_stdio(-EBADF, TAKE_FD(pipe_fds[1]), -EBADF) < 0)
  42                         _exit(EXIT_FAILURE);
  43
  44                 (void) close_all_fds(NULL, 0);
  45
  46                 execle("/usr/bin/getent", "getent", database, key, NULL, &empty_env);
  47                 execle("/bin/getent", "getent", database, key, NULL, &empty_env);
  48                 _exit(EXIT_FAILURE);
  49         }
  50
  51         pipe_fds[1] = safe_close(pipe_fds[1]);
  52
  53         *rpid = pid;
  54
  55         return pipe_fds[0];
  56 }
  57
  58 int change_uid_gid_raw(
  59                 uid_t uid,
  60                 gid_t gid,
  61                 const gid_t *supplementary_gids,
  62                 size_t n_supplementary_gids,
  63                 bool chown_stdio) {
  64
  65         if (!uid_is_valid(uid))
  66                 uid = 0;
  67         if (!gid_is_valid(gid))
  68                 gid = 0;
  69
  70         if (chown_stdio) {
  71                 (void) fchown(STDIN_FILENO, uid, gid);
  72                 (void) fchown(STDOUT_FILENO, uid, gid);
  73                 (void) fchown(STDERR_FILENO, uid, gid);
  74         }
  75
  76         if (setgroups(n_supplementary_gids, supplementary_gids) < 0)
  77                 return log_error_errno(errno, "Failed to set auxiliary groups: %m");
  78
  79         if (setresgid(gid, gid, gid) < 0)
  80                 return log_error_errno(errno, "setresgid() failed: %m");
  81
  82         if (setresuid(uid, uid, uid) < 0)
  83                 return log_error_errno(errno, "setresuid() failed: %m");
  84
  85         return 0;
  86 }
  87
  88 int change_uid_gid(const char *user, bool chown_stdio, char **ret_home) {
  89         char *x, *u, *g, *h;
  90         _cleanup_free_ gid_t *gids = NULL;
  91         _cleanup_free_ char *home = NULL, *line = NULL;
  92         _cleanup_fclose_ FILE *f = NULL;
  93         _cleanup_close_ int fd = -EBADF;
  94         unsigned n_gids = 0;
  95         uid_t uid;
  96         gid_t gid;
  97         pid_t pid;
  98         int r;
  99
 100         assert(ret_home);
 101
 102         if (!user || STR_IN_SET(user, "root", "0")) {
 103                 /* Reset everything fully to 0, just in case */
 104
 105                 r = reset_uid_gid();
 106                 if (r < 0)
 107                         return log_error_errno(r, "Failed to become root: %m");
 108
 109                 *ret_home = NULL;
 110                 return 0;
 111         }
 112
 113         /* First, get user credentials */
 114         fd = spawn_getent("passwd", user, &pid);
 115         if (fd < 0)
 116                 return fd;
 117
 118         f = take_fdopen(&fd, "r");
 119         if (!f)
 120                 return log_oom();
 121
 122         r = read_line(f, LONG_LINE_MAX, &line);
 123         if (r == 0)
 124                 return log_error_errno(SYNTHETIC_ERRNO(ESRCH),
 125                                        "Failed to resolve user %s.", user);
 126         if (r < 0)
 127                 return log_error_errno(r, "Failed to read from getent: %m");
 128
 129         (void) wait_for_terminate_and_check("getent passwd", pid, WAIT_LOG);
 130
 131         x = strchr(line, ':');
 132         if (!x)
 133                 return log_error_errno(SYNTHETIC_ERRNO(EIO),
 134                                        "/etc/passwd entry has invalid user field.");
 135
 136         u = strchr(x+1, ':');
 137         if (!u)
 138                 return log_error_errno(SYNTHETIC_ERRNO(EIO),
 139                                        "/etc/passwd entry has invalid password field.");
 140
 141         u++;
 142         g = strchr(u, ':');
 143         if (!g)
 144                 return log_error_errno(SYNTHETIC_ERRNO(EIO),
 145                                        "/etc/passwd entry has invalid UID field.");
 146
 147         *g = 0;
 148         g++;
 149         x = strchr(g, ':');
 150         if (!x)
 151                 return log_error_errno(SYNTHETIC_ERRNO(EIO),
 152                                        "/etc/passwd entry has invalid GID field.");
 153
 154         *x = 0;
 155         h = strchr(x+1, ':');
 156         if (!h)
 157                 return log_error_errno(SYNTHETIC_ERRNO(EIO),
 158                                        "/etc/passwd entry has invalid GECOS field.");
 159
 160         h++;
 161         x = strchr(h, ':');
 162         if (!x)
 163                 return log_error_errno(SYNTHETIC_ERRNO(EIO),
 164                                        "/etc/passwd entry has invalid home directory field.");
 165
 166         *x = 0;
 167
 168         r = parse_uid(u, &uid);
 169         if (r < 0)
 170                 return log_error_errno(SYNTHETIC_ERRNO(EIO),
 171                                        "Failed to parse UID of user.");
 172
 173         r = parse_gid(g, &gid);
 174         if (r < 0)
 175                 return log_error_errno(SYNTHETIC_ERRNO(EIO),
 176                                        "Failed to parse GID of user.");
 177
 178         home = strdup(h);
 179         if (!home)
 180                 return log_oom();
 181
 182         f = safe_fclose(f);
 183         line = mfree(line);
 184
 185         /* Second, get group memberships */
 186         fd = spawn_getent("initgroups", user, &pid);
 187         if (fd < 0)
 188                 return fd;
 189
 190         f = take_fdopen(&fd, "r");
 191         if (!f)
 192                 return log_oom();
 193
 194         r = read_line(f, LONG_LINE_MAX, &line);
 195         if (r == 0)
 196                 return log_error_errno(SYNTHETIC_ERRNO(ESRCH),
 197                                        "Failed to resolve user %s.", user);
 198         if (r < 0)
 199                 return log_error_errno(r, "Failed to read from getent: %m");
 200
 201         (void) wait_for_terminate_and_check("getent initgroups", pid, WAIT_LOG);
 202
 203         /* Skip over the username and subsequent separator whitespace */
 204         x = line;
 205         x += strcspn(x, WHITESPACE);
 206         x += strspn(x, WHITESPACE);
 207
 208         for (const char *p = x;;) {
 209                _cleanup_free_ char *word = NULL;
 210
 211                 r = extract_first_word(&p, &word, NULL, 0);
 212                 if (r < 0)
 213                         return log_error_errno(r, "Failed to parse group data from getent: %m");
 214                 if (r == 0)
 215                         break;
 216
 217                 if (!GREEDY_REALLOC(gids, n_gids+1))
 218                         return log_oom();
 219
 220                 r = parse_gid(word, &gids[n_gids++]);
 221                 if (r < 0)
 222                         return log_error_errno(r, "Failed to parse group data from getent: %m");
 223         }
 224
 225         r = mkdir_parents(home, 0775);
 226         if (r < 0)
 227                 return log_error_errno(r, "Failed to make home root directory: %m");
 228
 229         r = mkdir_safe(home, 0755, uid, gid, 0);
 230         if (r < 0 && !IN_SET(r, -EEXIST, -ENOTDIR))
 231                 return log_error_errno(r, "Failed to make home directory: %m");
 232
 233         r = change_uid_gid_raw(uid, gid, gids, n_gids, chown_stdio);
 234         if (r < 0)
 235                 return r;
 236
 237         if (ret_home)
 238                 *ret_home = TAKE_PTR(home);
 239
 240         return 0;
 241 }