From c87a9b855e12fafbafcd2af37fd53374cf965ce8 Mon Sep 17 00:00:00 2001
From: Reepca Russelstein <reepca@russelstein.xyz>
Date: Fri, 5 Sep 2025 01:59:12 -0500
Subject: [PATCH] daemon: Restore post-canonicalization permissions after
 moving.
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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>
---
 nix/libstore/build.cc |  8 ++++++--
 tests/store.scm       | 11 +++++++++++
 2 files changed, 17 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)
diff --git a/tests/store.scm b/tests/store.scm
index 112ea7e2fcb..16dcbf2396d 100644
--- a/tests/store.scm
+++ b/tests/store.scm
@@ -417,6 +417,17 @@
                      get-string-all)
                    a))))
 
+;; https://codeberg.org/guix/guix/issues/1104
+(test-equal "build outputs aren't writable"
+  #o555
+  (let ((drv (build-expression->derivation %store "writable-output"
+                                           `(begin
+                                              ,(random-text)
+                                              (mkdir %output)
+                                              (chmod %output #o755)))))
+    (build-derivations %store (list drv))
+    (stat:perms (stat (derivation->output-path drv "out")))))
+
 (unless (unprivileged-user-namespace-supported?)
   (test-skip 1))
 (test-equal "isolated environment"