Reject Composer trust mount overrides

scripts/ci/brotli-safe-composer.sh

@@ -20,7 +20,9 @@ floor='brotli-libs>=1.2.1-r0'
 # Refuses IMAGE unless its installed brotli-libs meets the floor and every
 # Brotli decoder its PHP links belongs to that package.
 check() {
-    docker run --rm --network none --user 0 --entrypoint sh "$1" -c '
+    local checked_image
+    checked_image=$1
+    docker run --rm --network none --user 0 --entrypoint sh "$checked_image" -c '
         set -eu
         apk info -e "$1" > /dev/null || { echo "Composer image lacks $1" >&2; exit 1; }
         for library in $(ldd "$(command -v php)" | awk "/libbrotlidec/ {print \$3}"); do

scripts/ci/run-composer.sh

@@ -17,9 +17,13 @@ here=$(dirname "$0")
 options=()
 while (($#)) && [[ $1 != -- ]]; do
     case "$1" in
-        *COMPOSER_CAFILE* | *COMPOSER_CAPATH* | --entrypoint* | --env-file*)
+        *COMPOSER_CAFILE* | *COMPOSER_CAPATH* | --entrypoint* | --env-file* | --volumes-from*)
             echo "run-composer.sh sets the CA pair and the entrypoint itself; refusing $1" >&2
             exit 2 ;;
+        */checked-ca*)
+            echo "run-composer.sh reserves /checked-ca for its checked CA pair; refusing $1" >&2
+            exit 2 ;;
+        *) ;;
     esac
     options+=("$1")
     shift

tests/Unit/Support/composer_trust_test.py

@@ -341,7 +341,15 @@ def wrapper(self, *arguments: str) -> tuple[subprocess.CompletedProcess[str], bo
     def test_the_caller_cannot_replace_the_ca_pair_or_the_entrypoint(self) -> None:
         for options in (["-e", "COMPOSER_CAFILE=/etc/ssl/certs/ca-certificates.crt"], ["-eCOMPOSER_CAFILE=/x"],
                         ["--env", "COMPOSER_CAPATH=/etc/ssl/certs"], ["--entrypoint=sh"], ["--entrypoint", "sh"],
-                        ["--env-file", "composer.env"]):
+                        ["--env-file", "composer.env"], ["-v", "/tmp/root.pem:/checked-ca/ca.pem:ro"],
+                        ["--volume=/tmp/trust:/checked-ca:ro"],
+                        ["--mount", "type=bind,src=/tmp/empty,dst=/checked-ca/no-ca-directory"],
+                        ["--mount=type=bind,src=/tmp/empty,dst=/checked-ca/no-ca-directory"],
+                        ["--tmpfs", "/checked-ca"], ["--tmpfs=/checked-ca"],
+                        ["--device", "/dev/null:/checked-ca/ca.pem"],
+                        ["--device=/dev/null:/checked-ca/ca.pem"],
+                        ["--volumes-from", "untrusted-container"],
+                        ["--volumes-from=untrusted-container"]):
             with self.subTest(options):
                 result, docker_called = self.wrapper("--rm", *options, "--", "install")
 
@@ -355,6 +363,12 @@ def test_composer_arguments_need_the_separator(self) -> None:
         self.assertEqual(2, result.returncode)
         self.assertFalse(docker_called)
 
+    def test_unrelated_docker_options_reach_the_pinned_image_builder(self) -> None:
+        result, docker_called = self.wrapper("--rm", "-v", "/tmp:/app", "--", "install")
+
+        self.assertNotEqual(2, result.returncode, result.stderr)
+        self.assertTrue(docker_called)
+
     def test_the_ca_pair_and_entrypoint_follow_the_callers_options(self) -> None:
         text = WRAPPER_SCRIPT.read_text()
         command = text[text.index("docker run --user"):]