Cygwin: fix up cached DOS file attributes after file creation

The file attributes after creating a file are not necessarily
identical to the attributes we passed as argument to NtCreateFile.
This results in subsequent operations like fchmod or facl to
set the DOS file attributes to unexpected values.

The fix is to request file attributes from the OS after file creation
and cache those.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

2 files changed, 36 insertions, 24 deletions

diff --git a/winsup/cygwin/fhandler.cc b/winsup/cygwin/fhandler.cc
index 2a07e6c..fc7c042 100644
--- a/winsup/cygwin/fhandler.cc
+++ b/winsup/cygwin/fhandler.cc
@@ -676,8 +676,6 @@ fhandler_base::open (int flags, mode_t mode)
 	    /* If mode has no write bits set, and ACLs are not used, we set
 	       the DOS R/O attribute. */
 	    file_attributes |= FILE_ATTRIBUTE_READONLY;
-	  /* The file attributes are needed for later use in, e.g. fchmod. */
-	  pc.file_attributes (file_attributes);
 	  /* Never set the WRITE_DAC flag here.  Calls to fstat may return
 	     wrong st_ctime information after calls to fchmod, fchown, etc
 	     because Windows only guarantees the update of metadata when
@@ -720,28 +718,38 @@ fhandler_base::open (int flags, mode_t mode)
 	goto done;
    }
 
-  /* Always create files using a NULL SD.  Create correct permission bits
-     afterwards, maintaining the owner and group information just like chmod.
-
-     This is done for two reasons.
-
-     On Windows filesystems we need to create the file with default
-     permissions to allow inheriting ACEs.  When providing an explicit DACL
-     in calls to [Nt]CreateFile, the created file will not inherit default
-     permissions from the parent object.  This breaks not only Windows
-     inheritance, but also POSIX ACL inheritance.
-
-     Another reason to do this are remote shares.  Files on a remote share
-     are created as the user used for authentication.  In a domain that's
-     usually the user you're logged in as.  Outside of a domain you're
-     authenticating using a local user account on the sharing machine.
-     If the SIDs of the client machine are used, that's entirely
-     unexpected behaviour.  Doing it like we do here creates the expected SD
-     in a domain as well as on standalone servers.
-     This is the result of a discussion on the samba-technical list, starting at
-     http://lists.samba.org/archive/samba-technical/2008-July/060247.html */
-  if (io.Information == FILE_CREATED && has_acls ())
-    set_created_file_access (fh, pc, mode);
+  if (io.Information == FILE_CREATED)
+    {
+      /* Correct file attributes are needed for later use in, e.g. fchmod. */
+      FILE_BASIC_INFORMATION fbi;
+
+      if (!NT_SUCCESS (NtQueryInformationFile (fh, &io, &fbi, sizeof fbi,
+					       FileBasicInformation)))
+	fbi.FileAttributes = file_attributes | FILE_ATTRIBUTE_ARCHIVE;
+      pc.file_attributes (fbi.FileAttributes);
+
+      /* Always create files using a NULL SD.  Create correct permission bits
+	 afterwards, maintaining the owner and group information just like
+	 chmod.  This is done for two reasons.
+
+	 On Windows filesystems we need to create the file with default
+	 permissions to allow inheriting ACEs.  When providing an explicit DACL
+	 in calls to [Nt]CreateFile, the created file will not inherit default
+	 permissions from the parent object.  This breaks not only Windows
+	 inheritance, but also POSIX ACL inheritance.
+
+	 Another reason to do this are remote shares.  Files on a remote share
+	 are created as the user used for authentication.  In a domain that's
+	 usually the user you're logged in as.  Outside of a domain you're
+	 authenticating using a local user account on the sharing machine.
+	 If the SIDs of the client machine are used, that's entirely unexpected
+	 behaviour.  Doing it like we do here creates the expected SD in a
+	 domain as well as on standalone servers.  This is the result of a
+	 discussion on the samba-technical list, starting at
+	 http://lists.samba.org/archive/samba-technical/2008-July/060247.html */
+      if (has_acls ())
+	set_created_file_access (fh, pc, mode);
+    }
 
   /* If you O_TRUNC a file on Linux, the data is truncated, but the EAs are
      preserved.  If you open a file on Windows with FILE_OVERWRITE{_IF} or
diff --git a/winsup/cygwin/release/3.3.3 b/winsup/cygwin/release/3.3.3
index e37844a..e8404be 100644
--- a/winsup/cygwin/release/3.3.3
+++ b/winsup/cygwin/release/3.3.3
@@ -18,3 +18,7 @@ Bug Fixes
   running bash in Windows Terminal and inserting an emoji does not
   work as expected.
   Addresses: https://github.com/git-for-windows/git/issues/3281
+
+- Fix long-standing problem that fchmod or facl on newly created files
+  screw up the DOS file attributes.
+  Addresses: https://cygwin.com/pipermail/cygwin/2021-November/249909.html