copy artifact/signature into/out of child container

entrypoint.sh

@@ -16,16 +16,24 @@ while IFS=  read -r f; do
   sign_file="$(basename "$f")"
   dest_sig="${sign_dir}/${sign_file}.sig"
   echo "Signing file $f. Signature file destination: ${dest_sig}"
-  docker run --rm \
+  # We can't use a volume mount because it will use the host volume, and we're
+  # not on the host, but in a container. So we'll create a container, copy
+  # the file to sign in place, get the signature and copy that back
+  container="$(docker create \
     -v /run/pcscd/pcscd.comm:/run/pcscd/pcscd.comm:ro \
-    -v "${PWD}":/home/user \
     -e INPUT_PIN \
     git.lerch.org/lobo/pkcs11:1 \
-    -s --id "${INPUT_SLOT}" -m SHA256-RSA-PKCS -i "$f" -o "${dest_sig}" --pin env:INPUT_PIN
+    -s --id "${INPUT_SLOT}" -m SHA256-RSA-PKCS -i artifact -o signature --pin env:INPUT_PIN)"
+  docker cp "$f" "${container}":/home/user/artifact
+  docker start -a "$container" # let container run, pick up the exit code
   ec=$?
   if [ $ec -ne 0 ]; then
+    docker rm "$container"
     exit $ec
   fi
+  # We are clear. Copy signature back into the workspace and remove the container
+  docker cp "${container}":/home/user/signature "${dest_sig}"
+  docker rm "${container}"
   if [ -n "${INPUT_PUBLIC_KEY}" ]; then
     echo "Public key specified. Uploading to sigstore public transparency log"
     rekor upload --artifact "$f" --signature "${dest_sig}" --pki-format x509 --public-key public_key