From 79efbb719383386051c72f2ee932eeca8e033e6b Mon Sep 17 00:00:00 2001
From: Olexa Bilaniuk <obilaniu@users.noreply.github.com>
Date: Thu, 9 May 2019 22:22:06 -0500
Subject: [PATCH] bpo-24538: Fix bug in shutil involving the copying of xattrs
 to read-only files. (PR-13212)

Extended attributes can only be set on user-writeable files, but shutil previously
first chmod()ed the destination file to the source's permissions and then tried to
copy xattrs. This will cause failures if attempting to copy read-only files with
xattrs, as occurs with Git clones on Lustre FS.
---
 Lib/shutil.py                                             | 4 +++-
 Lib/test/test_shutil.py                                   | 8 ++++++++
 Misc/ACKS                                                 | 1 +
 .../next/Library/2019-05-09-08-35-18.bpo-24538.WK8Y-k.rst | 3 +++
 4 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2019-05-09-08-35-18.bpo-24538.WK8Y-k.rst

diff --git a/Lib/shutil.py b/Lib/shutil.py
index 6cfe3738f6e..b2e8f5fd759 100644
--- a/Lib/shutil.py
+++ b/Lib/shutil.py
@@ -359,6 +359,9 @@ def lookup(name):
     mode = stat.S_IMODE(st.st_mode)
     lookup("utime")(dst, ns=(st.st_atime_ns, st.st_mtime_ns),
         follow_symlinks=follow)
+    # We must copy extended attributes before the file is (potentially)
+    # chmod()'ed read-only, otherwise setxattr() will error with -EACCES.
+    _copyxattr(src, dst, follow_symlinks=follow)
     try:
         lookup("chmod")(dst, mode, follow_symlinks=follow)
     except NotImplementedError:
@@ -382,7 +385,6 @@ def lookup(name):
                     break
             else:
                 raise
-    _copyxattr(src, dst, follow_symlinks=follow)
 
 def copy(src, dst, *, follow_symlinks=True):
     """Copy data and mode bits ("cp src dst"). Return the file's destination.
diff --git a/Lib/test/test_shutil.py b/Lib/test/test_shutil.py
index e709a5661bf..eeebb97ff69 100644
--- a/Lib/test/test_shutil.py
+++ b/Lib/test/test_shutil.py
@@ -531,12 +531,20 @@ def _raise_on_src(fname, *, follow_symlinks=True):
 
         # test that shutil.copystat copies xattrs
         src = os.path.join(tmp_dir, 'the_original')
+        srcro = os.path.join(tmp_dir, 'the_original_ro')
         write_file(src, src)
+        write_file(srcro, srcro)
         os.setxattr(src, 'user.the_value', b'fiddly')
+        os.setxattr(srcro, 'user.the_value', b'fiddly')
+        os.chmod(srcro, 0o444)
         dst = os.path.join(tmp_dir, 'the_copy')
+        dstro = os.path.join(tmp_dir, 'the_copy_ro')
         write_file(dst, dst)
+        write_file(dstro, dstro)
         shutil.copystat(src, dst)
+        shutil.copystat(srcro, dstro)
         self.assertEqual(os.getxattr(dst, 'user.the_value'), b'fiddly')
+        self.assertEqual(os.getxattr(dstro, 'user.the_value'), b'fiddly')
 
     @support.skip_unless_symlink
     @support.skip_unless_xattr
diff --git a/Misc/ACKS b/Misc/ACKS
index 300e7889407..dfb96375360 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -149,6 +149,7 @@ Stephen Bevan
 Ron Bickers
 Natalia B. Bidart
 Adrian von Bidder
+Olexa Bilaniuk
 David Binger
 Dominic Binks
 Philippe Biondi
diff --git a/Misc/NEWS.d/next/Library/2019-05-09-08-35-18.bpo-24538.WK8Y-k.rst b/Misc/NEWS.d/next/Library/2019-05-09-08-35-18.bpo-24538.WK8Y-k.rst
new file mode 100644
index 00000000000..e799f931bce
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-05-09-08-35-18.bpo-24538.WK8Y-k.rst
@@ -0,0 +1,3 @@
+In `shutil.copystat()`, first copy extended file attributes and then file
+permissions, since extended attributes can only be set on the destination
+while it is still writeable.