[bug#75810] [PATCH v5 04/14] daemon: Remount inputs as read-only.

[Ludovic Courtès]

* nix/libstore/build.cc (DerivationGoal::runChild): Remount ‘target’ as
read-only.

Reported-by: Reepca Russelstein <reepca@russelstein.xyz>
Change-Id: Ib7201bcf4363be566f205d23d17fe2f55d3ad666
---
 nix/libstore/build.cc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 193b279b88..3861a1ffd9 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -2107,8 +2107,15 @@ void DerivationGoal::runChild()
                     createDirs(dirOf(target));
                     writeFile(target, "");
                 }
+
+               /* Extra flags passed with MS_BIND are ignored, hence the
+                  extra MS_REMOUNT.  */
                 if (mount(source.c_str(), target.c_str(), "", MS_BIND, 0) == 
-1)
                     throw SysError(format("bind mount from `%1%' to `%2%' 
failed") % source % target);
+               if (source.compare(0, settings.nixStore.length(), 
settings.nixStore) == 0) {
+                    if (mount(source.c_str(), target.c_str(), "", MS_BIND | 
MS_REMOUNT | MS_RDONLY, 0) == -1)
+                         throw SysError(format("read-only remount of `%1%' 
failed") % target);
+               }
             }
 
             /* Bind a new instance of procfs on /proc to reflect our
-- 
2.48.1