gdbsupport/filestuff.cc

   1 /* Low-level file-handling.
   2    Copyright (C) 2012-2022 Free Software Foundation, Inc.
   3
   4    This file is part of GDB.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #include "common-defs.h"
  20 #include "filestuff.h"
  21 #include "gdb_vecs.h"
  22 #include <fcntl.h>
  23 #include <unistd.h>
  24 #include <sys/types.h>
  25 #include <sys/stat.h>
  26 #include <algorithm>
  27
  28 #ifdef USE_WIN32API
  29 #include <winsock2.h>
  30 #include <windows.h>
  31 #define HAVE_SOCKETS 1
  32 #elif defined HAVE_SYS_SOCKET_H
  33 #include <sys/socket.h>
  34 /* Define HAVE_F_GETFD if we plan to use F_GETFD.  */
  35 #define HAVE_F_GETFD F_GETFD
  36 #define HAVE_SOCKETS 1
  37 #endif
  38
  39 #ifdef HAVE_KINFO_GETFILE
  40 #include <sys/user.h>
  41 #include <libutil.h>
  42 #endif
  43
  44 #ifdef HAVE_SYS_RESOURCE_H
  45 #include <sys/resource.h>
  46 #endif /* HAVE_SYS_RESOURCE_H */
  47
  48 #ifndef O_CLOEXEC
  49 #define O_CLOEXEC 0
  50 #endif
  51
  52 #ifndef O_NOINHERIT
  53 #define O_NOINHERIT 0
  54 #endif
  55
  56 #ifndef SOCK_CLOEXEC
  57 #define SOCK_CLOEXEC 0
  58 #endif
  59
  60 \f
  61
  62 #ifndef HAVE_FDWALK
  63
  64 #include <dirent.h>
  65
  66 /* Replacement for fdwalk, if the system doesn't define it.  Walks all
  67    open file descriptors (though this implementation may walk closed
  68    ones as well, depending on the host platform's capabilities) and
  69    call FUNC with ARG.  If FUNC returns non-zero, stops immediately
  70    and returns the same value.  Otherwise, returns zero when
  71    finished.  */
  72
  73 static int
  74 fdwalk (int (*func) (void *, int), void *arg)
  75 {
  76   /* Checking __linux__ isn't great but it isn't clear what would be
  77      better.  There doesn't seem to be a good way to check for this in
  78      configure.  */
  79 #ifdef __linux__
  80   DIR *dir;
  81
  82   dir = opendir ("/proc/self/fd");
  83   if (dir != NULL)
  84     {
  85       struct dirent *entry;
  86       int result = 0;
  87
  88       for (entry = readdir (dir); entry != NULL; entry = readdir (dir))
  89         {
  90           long fd;
  91           char *tail;
  92
  93           errno = 0;
  94           fd = strtol (entry->d_name, &tail, 10);
  95           if (*tail != '\0' || errno != 0)
  96             continue;
  97           if ((int) fd != fd)
  98             {
  99               /* What can we do here really?  */
 100               continue;
 101             }
 102
 103           if (fd == dirfd (dir))
 104             continue;
 105
 106           result = func (arg, fd);
 107           if (result != 0)
 108             break;
 109         }
 110
 111       closedir (dir);
 112       return result;
 113     }
 114   /* We may fall through to the next case.  */
 115 #endif
 116 #ifdef HAVE_KINFO_GETFILE
 117   int nfd;
 118   gdb::unique_xmalloc_ptr<struct kinfo_file[]> fdtbl
 119     (kinfo_getfile (getpid (), &nfd));
 120   if (fdtbl != NULL)
 121     {
 122       for (int i = 0; i < nfd; i++)
 123         {
 124           if (fdtbl[i].kf_fd >= 0)
 125             {
 126               int result = func (arg, fdtbl[i].kf_fd);
 127               if (result != 0)
 128                 return result;
 129             }
 130         }
 131       return 0;
 132     }
 133   /* We may fall through to the next case.  */
 134 #endif
 135
 136   {
 137     int max, fd;
 138
 139 #if defined(HAVE_GETRLIMIT) && defined(RLIMIT_NOFILE)
 140     struct rlimit rlim;
 141
 142     if (getrlimit (RLIMIT_NOFILE, &rlim) == 0 && rlim.rlim_max != RLIM_INFINITY)
 143       max = rlim.rlim_max;
 144     else
 145 #endif
 146       {
 147 #ifdef _SC_OPEN_MAX
 148         max = sysconf (_SC_OPEN_MAX);
 149 #else
 150         /* Whoops.  */
 151         return 0;
 152 #endif /* _SC_OPEN_MAX */
 153       }
 154
 155     for (fd = 0; fd < max; ++fd)
 156       {
 157         struct stat sb;
 158         int result;
 159
 160         /* Only call FUNC for open fds.  */
 161         if (fstat (fd, &sb) == -1)
 162           continue;
 163
 164         result = func (arg, fd);
 165         if (result != 0)
 166           return result;
 167       }
 168
 169     return 0;
 170   }
 171 }
 172
 173 #endif /* HAVE_FDWALK */
 174
 175 \f
 176
 177 /* A vector holding all the fds open when notice_open_fds was called.  We
 178    don't use a hashtab because we don't expect there to be many open fds.  */
 179
 180 static std::vector<int> open_fds;
 181
 182 /* An fdwalk callback function used by notice_open_fds.  It puts the
 183    given file descriptor into the vec.  */
 184
 185 static int
 186 do_mark_open_fd (void *ignore, int fd)
 187 {
 188   open_fds.push_back (fd);
 189   return 0;
 190 }
 191
 192 /* See filestuff.h.  */
 193
 194 void
 195 notice_open_fds (void)
 196 {
 197   fdwalk (do_mark_open_fd, NULL);
 198 }
 199
 200 /* See filestuff.h.  */
 201
 202 void
 203 mark_fd_no_cloexec (int fd)
 204 {
 205   do_mark_open_fd (NULL, fd);
 206 }
 207
 208 /* See filestuff.h.  */
 209
 210 void
 211 unmark_fd_no_cloexec (int fd)
 212 {
 213   auto it = std::remove (open_fds.begin (), open_fds.end (), fd);
 214
 215   if (it != open_fds.end ())
 216     open_fds.erase (it);
 217   else
 218     gdb_assert_not_reached ("fd not found in open_fds");
 219 }
 220
 221 /* Helper function for close_most_fds that closes the file descriptor
 222    if appropriate.  */
 223
 224 static int
 225 do_close (void *ignore, int fd)
 226 {
 227   for (int val : open_fds)
 228     {
 229       if (fd == val)
 230         {
 231           /* Keep this one open.  */
 232           return 0;
 233         }
 234     }
 235
 236   close (fd);
 237   return 0;
 238 }
 239
 240 /* See filestuff.h.  */
 241
 242 void
 243 close_most_fds (void)
 244 {
 245   fdwalk (do_close, NULL);
 246 }
 247
 248 \f
 249
 250 /* This is a tri-state flag.  When zero it means we haven't yet tried
 251    O_CLOEXEC.  When positive it means that O_CLOEXEC works on this
 252    host.  When negative, it means that O_CLOEXEC doesn't work.  We
 253    track this state because, while gdb might have been compiled
 254    against a libc that supplies O_CLOEXEC, there is no guarantee that
 255    the kernel supports it.  */
 256
 257 static int trust_o_cloexec;
 258
 259 /* Mark FD as close-on-exec, ignoring errors.  Update
 260    TRUST_O_CLOEXEC.  */
 261
 262 static void
 263 mark_cloexec (int fd)
 264 {
 265 #ifdef HAVE_F_GETFD
 266   int old = fcntl (fd, F_GETFD, 0);
 267
 268   if (old != -1)
 269     {
 270       fcntl (fd, F_SETFD, old | FD_CLOEXEC);
 271
 272       if (trust_o_cloexec == 0)
 273         {
 274           if ((old & FD_CLOEXEC) != 0)
 275             trust_o_cloexec = 1;
 276           else
 277             trust_o_cloexec = -1;
 278         }
 279     }
 280 #endif /* HAVE_F_GETFD */
 281 }
 282
 283 /* Depending on TRUST_O_CLOEXEC, mark FD as close-on-exec.  */
 284
 285 static void
 286 maybe_mark_cloexec (int fd)
 287 {
 288   if (trust_o_cloexec <= 0)
 289     mark_cloexec (fd);
 290 }
 291
 292 #ifdef HAVE_SOCKETS
 293
 294 /* Like maybe_mark_cloexec, but for callers that use SOCK_CLOEXEC.  */
 295
 296 static void
 297 socket_mark_cloexec (int fd)
 298 {
 299   if (SOCK_CLOEXEC == 0 || trust_o_cloexec <= 0)
 300     mark_cloexec (fd);
 301 }
 302
 303 #endif
 304
 305 \f
 306
 307 /* See filestuff.h.  */
 308
 309 scoped_fd
 310 gdb_open_cloexec (const char *filename, int flags, unsigned long mode)
 311 {
 312   scoped_fd fd (open (filename, flags | O_CLOEXEC, mode));
 313
 314   if (fd.get () >= 0)
 315     maybe_mark_cloexec (fd.get ());
 316
 317   return fd;
 318 }
 319
 320 /* See filestuff.h.  */
 321
 322 gdb_file_up
 323 gdb_fopen_cloexec (const char *filename, const char *opentype)
 324 {
 325   FILE *result;
 326   /* Probe for "e" support once.  But, if we can tell the operating
 327      system doesn't know about close on exec mode "e" without probing,
 328      skip it.  E.g., the Windows runtime issues an "Invalid parameter
 329      passed to C runtime function" OutputDebugString warning for
 330      unknown modes.  Assume that if O_CLOEXEC is zero, then "e" isn't
 331      supported.  On MinGW, O_CLOEXEC is an alias of O_NOINHERIT, and
 332      "e" isn't supported.  */
 333   static int fopen_e_ever_failed_einval =
 334     O_CLOEXEC == 0 || O_CLOEXEC == O_NOINHERIT;
 335
 336   if (!fopen_e_ever_failed_einval)
 337     {
 338       char *copy;
 339
 340       copy = (char *) alloca (strlen (opentype) + 2);
 341       strcpy (copy, opentype);
 342       /* This is a glibc extension but we try it unconditionally on
 343          this path.  */
 344       strcat (copy, "e");
 345       result = fopen (filename, copy);
 346
 347       if (result == NULL && errno == EINVAL)
 348         {
 349           result = fopen (filename, opentype);
 350           if (result != NULL)
 351             fopen_e_ever_failed_einval = 1;
 352         }
 353     }
 354   else
 355     result = fopen (filename, opentype);
 356
 357   if (result != NULL)
 358     maybe_mark_cloexec (fileno (result));
 359
 360   return gdb_file_up (result);
 361 }
 362
 363 #ifdef HAVE_SOCKETS
 364 /* See filestuff.h.  */
 365
 366 int
 367 gdb_socketpair_cloexec (int domain, int style, int protocol,
 368                         int filedes[2])
 369 {
 370 #ifdef HAVE_SOCKETPAIR
 371   int result = socketpair (domain, style | SOCK_CLOEXEC, protocol, filedes);
 372
 373   if (result != -1)
 374     {
 375       socket_mark_cloexec (filedes[0]);
 376       socket_mark_cloexec (filedes[1]);
 377     }
 378
 379   return result;
 380 #else
 381   gdb_assert_not_reached ("socketpair not available on this host");
 382 #endif
 383 }
 384
 385 /* See filestuff.h.  */
 386
 387 int
 388 gdb_socket_cloexec (int domain, int style, int protocol)
 389 {
 390   int result = socket (domain, style | SOCK_CLOEXEC, protocol);
 391
 392   if (result != -1)
 393     socket_mark_cloexec (result);
 394
 395   return result;
 396 }
 397 #endif
 398
 399 /* See filestuff.h.  */
 400
 401 int
 402 gdb_pipe_cloexec (int filedes[2])
 403 {
 404   int result;
 405
 406 #ifdef HAVE_PIPE2
 407   result = pipe2 (filedes, O_CLOEXEC);
 408   if (result != -1)
 409     {
 410       maybe_mark_cloexec (filedes[0]);
 411       maybe_mark_cloexec (filedes[1]);
 412     }
 413 #else
 414 #ifdef HAVE_PIPE
 415   result = pipe (filedes);
 416   if (result != -1)
 417     {
 418       mark_cloexec (filedes[0]);
 419       mark_cloexec (filedes[1]);
 420     }
 421 #else /* HAVE_PIPE */
 422   gdb_assert_not_reached ("pipe not available on this host");
 423 #endif /* HAVE_PIPE */
 424 #endif /* HAVE_PIPE2 */
 425
 426   return result;
 427 }
 428
 429 /* See gdbsupport/filestuff.h.  */
 430
 431 bool
 432 is_regular_file (const char *name, int *errno_ptr)
 433 {
 434   struct stat st;
 435   const int status = stat (name, &st);
 436
 437   /* Stat should never fail except when the file does not exist.
 438      If stat fails, analyze the source of error and return true
 439      unless the file does not exist, to avoid returning false results
 440      on obscure systems where stat does not work as expected.  */
 441
 442   if (status != 0)
 443     {
 444       if (errno != ENOENT)
 445         return true;
 446       *errno_ptr = ENOENT;
 447       return false;
 448     }
 449
 450   if (S_ISREG (st.st_mode))
 451     return true;
 452
 453   if (S_ISDIR (st.st_mode))
 454     *errno_ptr = EISDIR;
 455   else
 456     *errno_ptr = EINVAL;
 457   return false;
 458 }
 459
 460 /* See gdbsupport/filestuff.h.  */
 461
 462 bool
 463 mkdir_recursive (const char *dir)
 464 {
 465   auto holder = make_unique_xstrdup (dir);
 466   char * const start = holder.get ();
 467   char *component_start = start;
 468   char *component_end = start;
 469
 470   while (1)
 471     {
 472       /* Find the beginning of the next component.  */
 473       while (*component_start == '/')
 474         component_start++;
 475
 476       /* Are we done?  */
 477       if (*component_start == '\0')
 478         return true;
 479
 480       /* Find the slash or null-terminator after this component.  */
 481       component_end = component_start;
 482       while (*component_end != '/' && *component_end != '\0')
 483         component_end++;
 484
 485       /* Temporarily replace the slash with a null terminator, so we can create
 486          the directory up to this component.  */
 487       char saved_char = *component_end;
 488       *component_end = '\0';
 489
 490       /* If we get EEXIST and the existing path is a directory, then we're
 491          happy.  If it exists, but it's a regular file and this is not the last
 492          component, we'll fail at the next component.  If this is the last
 493          component, the caller will fail with ENOTDIR when trying to
 494          open/create a file under that path.  */
 495       if (mkdir (start, 0700) != 0)
 496         if (errno != EEXIST)
 497           return false;
 498
 499       /* Restore the overwritten char.  */
 500       *component_end = saved_char;
 501       component_start = component_end;
 502     }
 503 }