src/nspawn/nspawn-setuid.c

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