X-Git-Url: https://git.gag.com/?a=blobdiff_plain;f=lib%2Fchdir-long.c;fp=lib%2Fchdir-long.c;h=28e24070e9bfef285c3435a01166dcd71cf4b31f;hb=a2016c1de6e4884f6c8ed5cc498f3bf821c25ca4;hp=0000000000000000000000000000000000000000;hpb=c7e61475680fa226bd9b8bdd469cd66914e630f5;p=debian%2Fgzip

diff --git a/lib/chdir-long.c b/lib/chdir-long.c
new file mode 100644
index 0000000..28e2407
--- /dev/null
+++ b/lib/chdir-long.c
@@ -0,0 +1,266 @@
+/* provide a chdir function that tries not to fail due to ENAMETOOLONG
+   Copyright (C) 2004-2010 Free Software Foundation, Inc.
+
+   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 3 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, see <http://www.gnu.org/licenses/>.  */
+
+/* written by Jim Meyering */
+
+#include <config.h>
+
+#include "chdir-long.h"
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <stdio.h>
+
+#ifndef PATH_MAX
+# error "compile this file only if your system defines PATH_MAX"
+#endif
+
+/* The results of openat() in this file are not leaked to any
+   single-threaded code that could use stdio.
+   FIXME - if the kernel ever adds support for multi-thread safety for
+   avoiding standard fds, then we should use openat_safer.  */
+
+struct cd_buf
+{
+  int fd;
+};
+
+static inline void
+cdb_init (struct cd_buf *cdb)
+{
+  cdb->fd = AT_FDCWD;
+}
+
+static inline int
+cdb_fchdir (struct cd_buf const *cdb)
+{
+  return fchdir (cdb->fd);
+}
+
+static inline void
+cdb_free (struct cd_buf const *cdb)
+{
+  if (0 <= cdb->fd)
+    {
+      bool close_fail = close (cdb->fd);
+      assert (! close_fail);
+    }
+}
+
+/* Given a file descriptor of an open directory (or AT_FDCWD), CDB->fd,
+   try to open the CDB->fd-relative directory, DIR.  If the open succeeds,
+   update CDB->fd with the resulting descriptor, close the incoming file
+   descriptor, and return zero.  Upon failure, return -1 and set errno.  */
+static int
+cdb_advance_fd (struct cd_buf *cdb, char const *dir)
+{
+  int new_fd = openat (cdb->fd, dir,
+                       O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
+  if (new_fd < 0)
+    return -1;
+
+  cdb_free (cdb);
+  cdb->fd = new_fd;
+
+  return 0;
+}
+
+/* Return a pointer to the first non-slash in S.  */
+static inline char *
+find_non_slash (char const *s)
+{
+  size_t n_slash = strspn (s, "/");
+  return (char *) s + n_slash;
+}
+
+/* This is a function much like chdir, but without the PATH_MAX limitation
+   on the length of the directory name.  A significant difference is that
+   it must be able to modify (albeit only temporarily) the directory
+   name.  It handles an arbitrarily long directory name by operating
+   on manageable portions of the name.  On systems without the openat
+   syscall, this means changing the working directory to more and more
+   `distant' points along the long directory name and then restoring
+   the working directory.  If any of those attempts to save or restore
+   the working directory fails, this function exits nonzero.
+
+   Note that this function may still fail with errno == ENAMETOOLONG, but
+   only if the specified directory name contains a component that is long
+   enough to provoke such a failure all by itself (e.g. if the component
+   has length PATH_MAX or greater on systems that define PATH_MAX).  */
+
+int
+chdir_long (char *dir)
+{
+  int e = chdir (dir);
+  if (e == 0 || errno != ENAMETOOLONG)
+    return e;
+
+  {
+    size_t len = strlen (dir);
+    char *dir_end = dir + len;
+    struct cd_buf cdb;
+    size_t n_leading_slash;
+
+    cdb_init (&cdb);
+
+    /* If DIR is the empty string, then the chdir above
+       must have failed and set errno to ENOENT.  */
+    assert (0 < len);
+    assert (PATH_MAX <= len);
+
+    /* Count leading slashes.  */
+    n_leading_slash = strspn (dir, "/");
+
+    /* Handle any leading slashes as well as any name that matches
+       the regular expression, m!^//hostname[/]*! .  Handling this
+       prefix separately usually results in a single additional
+       cdb_advance_fd call, but it's worthwhile, since it makes the
+       code in the following loop cleaner.  */
+    if (n_leading_slash == 2)
+      {
+        int err;
+        /* Find next slash.
+           We already know that dir[2] is neither a slash nor '\0'.  */
+        char *slash = memchr (dir + 3, '/', dir_end - (dir + 3));
+        if (slash == NULL)
+          {
+            errno = ENAMETOOLONG;
+            return -1;
+          }
+        *slash = '\0';
+        err = cdb_advance_fd (&cdb, dir);
+        *slash = '/';
+        if (err != 0)
+          goto Fail;
+        dir = find_non_slash (slash + 1);
+      }
+    else if (n_leading_slash)
+      {
+        if (cdb_advance_fd (&cdb, "/") != 0)
+          goto Fail;
+        dir += n_leading_slash;
+      }
+
+    assert (*dir != '/');
+    assert (dir <= dir_end);
+
+    while (PATH_MAX <= dir_end - dir)
+      {
+        int err;
+        /* Find a slash that is PATH_MAX or fewer bytes away from dir.
+           I.e. see if there is a slash that will give us a name of
+           length PATH_MAX-1 or less.  */
+        char *slash = memrchr (dir, '/', PATH_MAX);
+        if (slash == NULL)
+          {
+            errno = ENAMETOOLONG;
+            return -1;
+          }
+
+        *slash = '\0';
+        assert (slash - dir < PATH_MAX);
+        err = cdb_advance_fd (&cdb, dir);
+        *slash = '/';
+        if (err != 0)
+          goto Fail;
+
+        dir = find_non_slash (slash + 1);
+      }
+
+    if (dir < dir_end)
+      {
+        if (cdb_advance_fd (&cdb, dir) != 0)
+          goto Fail;
+      }
+
+    if (cdb_fchdir (&cdb) != 0)
+      goto Fail;
+
+    cdb_free (&cdb);
+    return 0;
+
+   Fail:
+    {
+      int saved_errno = errno;
+      cdb_free (&cdb);
+      errno = saved_errno;
+      return -1;
+    }
+  }
+}
+
+#if TEST_CHDIR
+
+# include "closeout.h"
+# include "error.h"
+
+char *program_name;
+
+int
+main (int argc, char *argv[])
+{
+  char *line = NULL;
+  size_t n = 0;
+  int len;
+
+  program_name = argv[0];
+  atexit (close_stdout);
+
+  len = getline (&line, &n, stdin);
+  if (len < 0)
+    {
+      int saved_errno = errno;
+      if (feof (stdin))
+        exit (0);
+
+      error (EXIT_FAILURE, saved_errno,
+             "reading standard input");
+    }
+  else if (len == 0)
+    exit (0);
+
+  if (line[len-1] == '\n')
+    line[len-1] = '\0';
+
+  if (chdir_long (line) != 0)
+    error (EXIT_FAILURE, errno,
+           "chdir_long failed: %s", line);
+
+  if (argc <= 1)
+    {
+      /* Using `pwd' here makes sense only if it is a robust implementation,
+         like the one in coreutils after the 2004-04-19 changes.  */
+      char const *cmd = "pwd";
+      execlp (cmd, (char *) NULL);
+      error (EXIT_FAILURE, errno, "%s", cmd);
+    }
+
+  fclose (stdin);
+  fclose (stderr);
+
+  exit (EXIT_SUCCESS);
+}
+#endif
+
+/*
+Local Variables:
+compile-command: "gcc -DTEST_CHDIR=1 -g -O -W -Wall chdir-long.c libcoreutils.a"
+End:
+*/