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List: grub-devel
Subject: Re: [PATCH] efi: Handle NULL return value when getting loaded image protocol
From: Ard Biesheuvel <ardb () kernel ! org>
Date: 2023-05-24 17:18:11
Message-ID: CAMj1kXE+cyHs_cMOh0NmsJ2TwPWWO7RBWZrQKKDUcAaM1q_35w () mail ! gmail ! com
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On Wed, 24 May 2023 at 19:15, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> The EFI spec mandates that the handle produced by the LoadImage boot
> service has a LoadedImage protocol instance installed on it, but for
> robustness, we should still deal with a NULL return value from the
> helper routine that obtains this protocol pointer.
>
> If this happens, don't try to start the image but unload it and return
> an error.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> grub-core/loader/efi/linux.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/grub-core/loader/efi/linux.c b/grub-core/loader/efi/linux.c
> index 90ad1a7b82a76066..b434c56ae67d665e 100644
> --- a/grub-core/loader/efi/linux.c
> +++ b/grub-core/loader/efi/linux.c
> @@ -214,6 +214,11 @@ grub_arch_efi_linux_boot_image (grub_addr_t addr, grub_size_t size, char *args)
>
> /* Convert command line to UCS-2 */
> loaded_image = grub_efi_get_loaded_image (image_handle);
> + if (loaded_image == NULL)
> + {
> + grub_error (GRUB_ERR_BAD_FIRMWARE, "missing loaded_image proto");
> + goto unload;
> + }
> loaded_image->load_options_size = len =
> (grub_strlen (args) + 1) * sizeof (grub_efi_char16_t);
> loaded_image->load_options =
> @@ -228,6 +233,7 @@ grub_arch_efi_linux_boot_image (grub_addr_t addr, grub_size_t size, char *args)
> grub_dprintf ("linux", "starting image %p\n", image_handle);
> status = b->start_image (image_handle, 0, NULL);
>
> +unload:
Uhm this is slightly bogus - apologies. The free_pages call still
dereferences loaded_image
I'll send a v2 right away.
> /* When successful, not reached */
> b->unload_image (image_handle);
> grub_efi_free_pages ((grub_addr_t) loaded_image->load_options,
> --
> 2.39.2
>
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