efi stub: accept it if our loaded image has no FilePath field set

The firmware spec doesn't really say whether FilePath of the LoadedImage
protocol may be NULL or not. So far we assumed it to be non-NULL, but
apparently the FreeBSD UEFI chainloader sets it to NULL. Handle this
gracefully.

(Noticed and tracked down by Alexander Schreiber)

Fixes: #18733
(cherry picked from commit 685097b9cadf92d21dfa857c3a7ddc1ba115088e)

diff --git a/src/boot/efi/stub.c b/src/boot/efi/stub.c
index a09f47c71194600d4b0a87b767b78bc1bf816d2a..3f267917ed729904a3c66f38b6916f638b6e5e35 100644 (file)
--- a/src/boot/efi/stub.c
+++ b/src/boot/efi/stub.c
@@ -92,8 +92,14 @@ EFI_STATUS efi_main(EFI_HANDLE image, EFI_SYSTEM_TABLE *sys_table) {
                 if (disk_get_part_uuid(loaded_image->DeviceHandle, uuid) == EFI_SUCCESS)
                         efivar_set(L"LoaderDevicePartUUID", uuid, FALSE);
 
-        /* if LoaderImageIdentifier is not set, assume the image with this stub was loaded directly from UEFI */
-        if (efivar_get_raw(&loader_guid, L"LoaderImageIdentifier", NULL, NULL) != EFI_SUCCESS) {
+        /* If LoaderImageIdentifier is not set, assume the image with this stub was loaded directly from the
+         * UEFI firmware without any boot loader, and hence set the LoaderImageIdentifier ourselves. Note
+         * that some boot chain loaders neither set LoaderImageIdentifier nor make FilePath available to us,
+         * in which case there's simple nothing to set for us. (The UEFI spec doesn't really say who's wrong
+         * here, i.e. whether FilePath may be NULL or not, hence handle this gracefully and check if FilePath
+         * is non-NULL explicitly.) */
+        if (efivar_get_raw(&loader_guid, L"LoaderImageIdentifier", NULL, NULL) != EFI_SUCCESS &&
+            loaded_image->FilePath) {
                 _cleanup_freepool_ CHAR16 *s;
 
                 s = DevicePathToStr(loaded_image->FilePath);