daemon: Copy network config files into chroot instead of mounting.

Config files like /etc/services may be symbolic links to files not available
in the build environment; copy them instead of creating dangling symlinks.

This also reverts 425aa1bf7c35839f5e500515ff3b5a861a7533d6, which would
potentially create dangling symlinks in the chroot, as reported by @cnx in
guix/guix#9072.

* nix/libstore/build.cc (DerivationGoal::startBuilder): copy network config
  files.

Fixes: guix/guix#4225
Change-Id: I38fc6374c5cecdcd16de06161db00b3825688f2a
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Modified-by: Ludovic Courtès <ludo@gnu.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index e72a0165987..85be95d557f 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -2826,11 +2826,11 @@ void DerivationGoal::startBuilder()
             }
             for (auto & file : files) {
                 if (pathExists(file)) {
-                    /* On Guix System, /etc/services is a symlink; likewise,
-                       on systemd-based system, /etc/resolv.conf is a symlink.
-                       Dereference them.  */
-                    ctx.filesInChroot[file] = canonPath(file, true);
-                    ctx.readOnlyFilesInChroot.insert(file);
+                    /* Copy files into chroot instead of bind-mounting in case
+                       they are symbolic links that won't resolve on the
+                       inside. */
+                    string contents = readFile(file);
+                    writeFile(chrootRootDir + file, contents);
                 }
             }
         }