bug#10257: 23.3.1 Cygwin: network drives - file is write protected (false positive)

[Ken Brown <kbrown@cornell.edu>]

On 12/15/2011 9:42 AM, Ken Brown wrote:
> On 12/14/2011 11:04 PM, Eli Zaretskii wrote:
>>> How does the following patch look?
>>
>> Looks fine to me, if it does the job.
>
> Thanks.
>
> It works for me, but I'd like Jari to confirm.

Jari has confirmed in private email that it works, but he has proposed 
making it slightly more permissive and having check_writable return 
success if either UID or GID is -1.  The rationale is the same as 
before:  If euidaccess returns failure but either UID or GID is -1, then 
the result of euidaccess is unreliable.  The revised patch is below.

Eli, do you see any problem with this extra permissiveness?

Stefan, is it OK to apply the patch to the trunk, or would you rather I 
wait for 24.2?

Ken

=== modified file 'src/fileio.c'
--- src/fileio.c        2011-12-05 08:55:25 +0000
+++ src/fileio.c        2011-12-16 19:32:23 +0000
@@ -2416,15 +2416,27 @@
    return (st.st_mode & S_IWRITE || S_ISDIR (st.st_mode));
  #else /* not MSDOS */
  #ifdef HAVE_EUIDACCESS
-  return (euidaccess (filename, 2) >= 0);
-#else
+  int res = (euidaccess (filename, 2) >= 0);
+#ifdef CYGWIN
+  /* euidaccess may have returned failure because Cygwin couldn't
+     determine the file's UID or GID; if so, we return success. */
+  if (!res)
+    {
+      struct stat st;
+      if (stat (filename, &st) < 0)
+        return 0;
+      res = (st.st_uid == -1 || st.st_gid == -1);
+    }
+#endif /* CYGWIN */
+  return res;
+#else /* not HAVE_EUIDACCESS */
    /* Access isn't quite right because it uses the real uid
       and we really want to test with the effective uid.
       But Unix doesn't give us a right way to do it.
       Opening with O_WRONLY could work for an ordinary file,
       but would lose for directories.  */
    return (access (filename, 2) >= 0);
-#endif
+#endif /* not HAVE_EUIDACCESS */
  #endif /* not MSDOS */
  }