daemon: Restore post-canonicalization permissions after moving.

At this point the value of 'st.st_mode' is from before canonicalization, so
restoring to that will undo the permissions aspect of the canonicalization for
a top-level directory store item.

Fixes #1104, introduced in
ae18b3d9e6 (https://codeberg.org/guix/guix/commit/ae18b3d9e6bd0c184505a094851448d08555e23e).

* nix/libstore/build.cc (DerivationGoal::registerOutputs): update 'st' with
  post-canonicalization permissions before making actualPath
  temporarily-writable.
* tests/store.scm ("build outputs aren't writable"): new test.

Change-Id: I5e5eaa79fa6b7f81e1d12fd285883c762a22ce5a
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 0a4de96d51d..a48214a9c0a 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -3139,10 +3139,14 @@ void DerivationGoal::registerOutputs()
               replaceValidPath(path, actualPath);
             else
                 if (buildMode != bmCheck) {
-                    if (S_ISDIR(st.st_mode))
+                    if (S_ISDIR(st.st_mode)) {
+                        if (lstat(actualPath.c_str(), &st) == -1)
+                            throw SysError(format("getting canonicalized permissions of directory `%1%'") % actualPath);
                         /* Change mode on the directory to allow for
                            rename(2).  */
-                        chmod(actualPath.c_str(), st.st_mode | 0700);
+                        if (chmod(actualPath.c_str(), st.st_mode | 0700) == -1)
+                            throw SysError(format("making `%1%' writable for move from chroot to store") % actualPath);
+                    }
                     if (rename(actualPath.c_str(), path.c_str()) == -1)
                         throw SysError(format("moving build output `%1%' from the chroot to the store") % path);
                     if (S_ISDIR(st.st_mode) && chmod(path.c_str(), st.st_mode) == -1)