On Linux, make the Nix store really read-only by using the immutable bit

I was bitten one time too many by Python modifying the Nix store by
creating *.pyc files when run as root.  On Linux, we can prevent this
by setting the immutable bit on files and directories (as in ‘chattr
+i’).  This isn't supported by all filesystems, so it's not an error
if setting the bit fails.  The immutable bit is cleared by the garbage
collector before deleting a path.  The only tricky aspect is in
optimiseStore(), since it's forbidden to create hard links to an
immutable file.  Thus optimiseStore() temporarily clears the immutable
bit before creating the link.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libutil/Makefile.am b/src/libutil/Makefile.am
index 98f32633b..a326060cf 100644
--- a/src/libutil/Makefile.am
+++ b/src/libutil/Makefile.am
@@ -1,12 +1,12 @@
 pkglib_LTLIBRARIES = libutil.la
 
 libutil_la_SOURCES = util.cc hash.cc serialise.cc \
-  archive.cc xml-writer.cc
+  archive.cc xml-writer.cc immutable.cc
 
 libutil_la_LIBADD = ../boost/format/libformat.la ${aterm_lib} ${sqlite_lib}
 
 pkginclude_HEADERS = util.hh hash.hh serialise.hh \
-  archive.hh xml-writer.hh types.hh
+  archive.hh xml-writer.hh types.hh immutable.hh
 
 if !HAVE_OPENSSL
 libutil_la_SOURCES += \