Merge pull request #10482 from tweag/fix-symlink-in-sandbox

Fix the access of symlinks to host files in the sandbox

src/libstore/build/local-derivation-goal.cc

@@ -1823,11 +1823,18 @@ void LocalDerivationGoal::runChild()
                     if (pathExists(path))
                         ss.push_back(path);
 
-                if (settings.caFile != "")
+                if (settings.caFile != "" && pathExists(settings.caFile)) {
-                    pathsInChroot.try_emplace("/etc/ssl/certs/ca-certificates.crt", settings.caFile, true);
+                    Path caFile = settings.caFile;
+                    pathsInChroot.try_emplace("/etc/ssl/certs/ca-certificates.crt", canonPath(caFile, true), true);
+                }
             }
 
-            for (auto & i : ss) pathsInChroot.emplace(i, i);
+            for (auto & i : ss) {
+                // For backwards-compatibiliy, resolve all the symlinks in the
+                // chroot paths
+                auto canonicalPath = canonPath(i, true);
+                pathsInChroot.emplace(i, canonicalPath);
+            }
 
             /* Bind-mount all the directories from the "host"
                filesystem that we want in the chroot

tests/functional/linux-sandbox.sh

@@ -60,7 +60,13 @@ testCert () {
 
 nocert=$TEST_ROOT/no-cert-file.pem
 cert=$TEST_ROOT/some-cert-file.pem
+symlinkcert=$TEST_ROOT/symlink-cert-file.pem
+transitivesymlinkcert=$TEST_ROOT/transitive-symlink-cert-file.pem
+symlinkDir=$TEST_ROOT/symlink-dir
 echo -n "CERT_CONTENT" > $cert
+ln -s $cert $symlinkcert
+ln -s $symlinkcert $transitivesymlinkcert
+ln -s $TEST_ROOT $symlinkDir
 
 # No cert in sandbox when not a fixed-output derivation
 testCert missing normal       "$cert"
@@ -74,5 +80,14 @@ testCert missing fixed-output "$nocert"
 # Cert in sandbox when ssl-cert-file is set to an existing file
 testCert present fixed-output "$cert"
 
+# Cert in sandbox when ssl-cert-file is set to a (potentially transitive) symlink to an existing file
+testCert present fixed-output "$symlinkcert"
+testCert present fixed-output "$transitivesymlinkcert"
+
 # Symlinks should be added in the sandbox directly and not followed
-nix-sandbox-build symlink-derivation.nix
+nix-sandbox-build symlink-derivation.nix -A depends_on_symlink
+nix-sandbox-build symlink-derivation.nix -A test_sandbox_paths \
+    --option extra-sandbox-paths "/file=$cert" \
+    --option extra-sandbox-paths "/dir=$TEST_ROOT" \
+    --option extra-sandbox-paths "/symlinkDir=$symlinkDir" \
+    --option extra-sandbox-paths "/symlink=$symlinkcert"

tests/functional/symlink-derivation.nix

@@ -15,7 +15,8 @@ let
     '';
   };
 in
-mkDerivation {
+{
+  depends_on_symlink = mkDerivation {
     name = "depends-on-symlink";
     buildCommand = ''
       (
@@ -30,7 +31,29 @@ mkDerivation {
         [[ -L ${symlink_to_not_in_store} ]]
         [[ $(readlink ${symlink_to_not_in_store}) == ${builtins.toString ./.} ]]
         (! ls ${symlink_to_not_in_store}/)
+
+        # Native paths
       )
       echo "Success!" > $out
     '';
+  };
+
+  test_sandbox_paths = mkDerivation {
+    # Depends on the caller to set a bunch of `--sandbox-path` arguments
+    name = "test-sandbox-paths";
+    buildCommand = ''
+      (
+        set -x
+        [[ -f /file ]]
+        [[ -d /dir ]]
+
+        # /symlink and /symlinkDir should be available as raw symlinks
+        # (pointing to files outside of the sandbox)
+        [[ -L /symlink ]] && [[ ! -e $(readlink /symlink) ]]
+        [[ -L /symlinkDir ]] && [[ ! -e $(readlink /symlinkDir) ]]
+      )
+
+      touch $out
+    '';
+  };
 }