osx: patch .pax.gz files in pkg bundles so they extract as root (issue4081)

The packages has to be installed by root but they would be installed
insecurely, owned by the uid of the unprivileged user that made the package.
The local user with that uid could thus write to /usr/local/bin/hg .

bdist_mpkg calls out to pax to create the package, but pax do apparently not
have the power to control what it is writing.

Instead, patch the pax files and set their uid fields to 0 before they are
wrapped in a dmg.

contrib/fixpax.py

@@ -0,0 +1,60
+# fixpax - fix ownership in bdist_mpkg output
+#
+# Copyright 2015 Matt Mackall <[e-mail]>
+#
+# This software may be used and distributed according to the terms of the
+# MIT license (http://opensource.org/licenses/MIT)
+
+"""Set file ownership to 0 in an Archive.pax.gz.
+Suitable for fixing files bdist_mpkg output:
+*.mpkg/Contents/Packages/*.pkg/Contents/Archive.pax.gz
+"""
+
+import sys, os, gzip
+
+def fixpax(iname, oname):
+    i = gzip.GzipFile(iname)
+    o = gzip.GzipFile(oname, "w")
+
+    while True:
+        magic = i.read(6)
+        dev = i.read(6)
+        ino = i.read(6)
+        mode = i.read(6)
+        i.read(6) # uid
+        i.read(6) # gid
+        nlink = i.read(6)
+        rdev = i.read(6)
+        mtime = i.read(11)
+        namesize = i.read(6)
+        filesize = i.read(11)
+        name = i.read(int(namesize, 8))
+        data = i.read(int(filesize, 8))
+
+        o.write(magic)
+        o.write(dev)
+        o.write(ino)
+        o.write(mode)
+        o.write("000000")
+        o.write("000000")
+        o.write(nlink)
+        o.write(rdev)
+        o.write(mtime)
+        o.write(namesize)
+        o.write(filesize)
+        o.write(name)
+        o.write(data)
+
+        if name.startswith("TRAILER!!!"):
+            o.write(i.read())
+            break
+
+    o.close()
+    i.close()
+
+if __name__ == '__main__':
+    for iname in sys.argv[1:]:
+        print 'fixing file ownership in %s' % iname
+        oname = sys.argv[1] + '.tmp'
+        fixpax(iname, oname)
+        os.rename(oname, iname)

Makefile

@@ -140,6 +140,7 osx:
 	   (echo "Missing bdist_mpkg (easy_install bdist_mpkg)"; false)
 	rm -rf dist/mercurial-*.mpkg
 	python -m bdist_mpkg.script_bdist_mpkg setup.py --
+	python contrib/fixpax.py dist/mercurial-*.mpkg/Contents/Packages/*.pkg/Contents/Archive.pax.gz
 	mkdir -p packages/osx
 	N=`cd dist && echo mercurial-*.mpkg | sed 's,\.mpkg$$,,'` && hdiutil create -srcfolder dist/$$N.mpkg/ -scrub -volname "$$N" -ov packages/osx/$$N.dmg
 	rm -rf dist/mercurial-*.mpkg