[newlib-cygwin] Cygwin: fix fchown on sockets that are not socket files

[Ken Brown <kbrown@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=cb0e71d3f8e0d1a60f36efc48b57864f1ef6efa7

commit cb0e71d3f8e0d1a60f36efc48b57864f1ef6efa7
Author: Ken Brown <kbrown@cornell.edu>
Date:   Mon Feb 22 09:50:34 2021 -0500

    Cygwin: fix fchown on sockets that are not socket files
    
    If fchown(2) is called on an AF_LOCAL or AF_UNIX socket that is not a
    socket file, the current code calls fhandler_disk_file::fchown in most
    cases.  The latter expects to be operating on a disk file and uses the
    socket's io_handle, which is not a file handle.
    
    Fix this by calling fhandler_disk_file::fchown only if the
    fhandler_socket object is a file (determined by testing dev().isfs()).

Diff:
---
 winsup/cygwin/fhandler_socket_local.cc | 6 +++++-
 winsup/cygwin/fhandler_socket_unix.cc  | 8 +++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/fhandler_socket_local.cc b/winsup/cygwin/fhandler_socket_local.cc
index d1faa079a..349ade897 100644
--- a/winsup/cygwin/fhandler_socket_local.cc
+++ b/winsup/cygwin/fhandler_socket_local.cc
@@ -724,8 +724,12 @@ fhandler_socket_local::fchmod (mode_t newmode)
 int
 fhandler_socket_local::fchown (uid_t uid, gid_t gid)
 {
-  if (get_sun_path () && get_sun_path ()[0] == '\0')
+  if (!dev ().isfs ())
+    /* fchown called on a socket. */
     return fhandler_socket_wsock::fchown (uid, gid);
+
+  /* chown/lchown on a socket file.  [We won't get here if fchown is
+     called on a socket opened w/ O_PATH.] */
   fhandler_disk_file fh (pc);
   return fh.fchown (uid, gid);
 }
diff --git a/winsup/cygwin/fhandler_socket_unix.cc b/winsup/cygwin/fhandler_socket_unix.cc
index e08e9bdd9..573864b9f 100644
--- a/winsup/cygwin/fhandler_socket_unix.cc
+++ b/winsup/cygwin/fhandler_socket_unix.cc
@@ -2395,10 +2395,12 @@ fhandler_socket_unix::fchmod (mode_t newmode)
 int
 fhandler_socket_unix::fchown (uid_t uid, gid_t gid)
 {
-  if (sun_path ()
-      && (sun_path ()->un_len <= (socklen_t) sizeof (sa_family_t)
-	  || sun_path ()->un.sun_path[0] == '\0'))
+  if (!dev ().isfs ())
+    /* fchown called on a socket. */
     return fhandler_socket::fchown (uid, gid);
+
+  /* chown/lchown on a socket file.  [We won't get here if fchown is
+     called on a socket opened w/ O_PATH.] */
   fhandler_disk_file fh (pc);
   return fh.fchown (uid, gid);
 }