Override fopen more carefully.

[gnulib.git] / lib / chown.c

diff --git a/lib/chown.c b/lib/chown.c
index 1d3346d..3582b04 100644 (file)
--- a/lib/chown.c
+++ b/lib/chown.c
@@ -1,11 +1,12 @@
 /* provide consistent interface to chown for systems that don't interpret
    an ID of -1 as meaning `don't change the corresponding ID'.
-   Copyright (C) 1997 Free Software Foundation, Inc.
 
-   This program is free software; you can redistribute it and/or modify
+   Copyright (C) 1997, 2004, 2005, 2006, 2007 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 2, or (at your option)
-   any later version.
+   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
@@ -13,32 +14,46 @@
    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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 /* written by Jim Meyering */
 
 #include <config.h>
+
+/* Specification.  */
+#include <unistd.h>
+
+#include <stdbool.h>
 #include <sys/types.h>
-#ifdef HAVE_UNISTD_H
-# include <unistd.h>
-#endif
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+
+/* Below we refer to the system's chown().  */
+#undef chown
+
+/* The results of open() in this file are not used with fchdir,
+   therefore save some unnecessary work in fchdir.c.  */
+#undef open
+#undef close
 
-/* FIXME: describe.  */
+/* Provide a more-closely POSIX-conforming version of chown on
+   systems with one or both of the following problems:
+   - chown doesn't treat an ID of -1 as meaning
+   `don't change the corresponding ID'.
+   - chown doesn't dereference symlinks.  */
 
 int
-chown (file, gid, uid)
-     const char *file;
-     gid_t git;
-     uid_t uit;
+rpl_chown (const char *file, uid_t uid, gid_t gid)
 {
+#if CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE
   if (gid == (gid_t) -1 || uid == (uid_t) -1)
     {
       struct stat file_stats;
 
       /* Stat file to get id(s) that should remain unchanged.  */
       if (stat (file, &file_stats))
-       return 1;
+       return -1;
 
       if (gid == (gid_t) -1)
        gid = file_stats.st_gid;
@@ -46,8 +61,43 @@ chown (file, gid, uid)
       if (uid == (uid_t) -1)
        uid = file_stats.st_uid;
     }
+#endif
 
-#undef chown
+#if CHOWN_MODIFIES_SYMLINK
+  {
+    /* Handle the case in which the system-supplied chown function
+       does *not* follow symlinks.  Instead, it changes permissions
+       on the symlink itself.  To work around that, we open the
+       file (but this can fail due to lack of read or write permission) and
+       use fchown on the resulting descriptor.  */
+    int open_flags = O_NONBLOCK | O_NOCTTY;
+    int fd = open (file, O_RDONLY | open_flags);
+    if (0 <= fd
+       || (errno == EACCES
+           && 0 <= (fd = open (file, O_WRONLY | open_flags))))
+      {
+       int result = fchown (fd, uid, gid);
+       int saved_errno = errno;
+
+       /* POSIX says fchown can fail with errno == EINVAL on sockets,
+          so fall back on chown in that case.  */
+       struct stat sb;
+       bool fchown_socket_failure =
+         (result != 0 && saved_errno == EINVAL
+          && fstat (fd, &sb) == 0 && S_ISFIFO (sb.st_mode));
+
+       close (fd);
+
+       if (! fchown_socket_failure)
+         {
+           errno = saved_errno;
+           return result;
+         }
+      }
+    else if (errno != EACCES)
+      return -1;
+  }
+#endif
 
-  return chown (file, gid, uid);
+  return chown (file, uid, gid);
 }