linux-kernel - Re: [PATCH v2 1/1] efivarfs: fix statfs() on efivarfs

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Date:   Sun, 10 Sep 2023 15:08:37 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
Cc:     Jeremy Kerr <jk@...abs.org>, Anisse Astier <an.astier@...teo.com>,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] efivarfs: fix statfs() on efivarfs

On Sun, 10 Sept 2023 at 06:53, Heinrich Schuchardt
<heinrich.schuchardt@...onical.com> wrote:
>
> Some firmware (notably U-Boot) provides GetVariable() and
> GetNextVariableName() but not QueryVariableInfo().
>
> With commit d86ff3333cb1 ("efivarfs: expose used and total size") the
> statfs syscall was broken for such firmware.
>
> If QueryVariableInfo() does not exist or returns an error, just report the
> file-system size as 0 as statfs_simple() previously did.
>
> Fixes: d86ff3333cb1 ("efivarfs: expose used and total size")
> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
> ---
> v2:
>         initialize remaining_space to 0

Thanks for the patch, and apologies for the oversight.

> ---
>  fs/efivarfs/super.c | 20 ++++++++++++--------
>  1 file changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
> index e028fafa04f3..3893aae6a9be 100644
> --- a/fs/efivarfs/super.c
> +++ b/fs/efivarfs/super.c
> @@ -29,14 +29,9 @@ static int efivarfs_statfs(struct dentry *dentry, struct kstatfs *buf)
>         const u32 attr = EFI_VARIABLE_NON_VOLATILE |
>                          EFI_VARIABLE_BOOTSERVICE_ACCESS |
>                          EFI_VARIABLE_RUNTIME_ACCESS;
> -       u64 storage_space, remaining_space, max_variable_size;
> +       u64 storage_space, remaining_space = 0, max_variable_size;

Shouldn't storage_space be set to 0 too?

>         efi_status_t status;
>
> -       status = efivar_query_variable_info(attr, &storage_space, &remaining_space,
> -                                           &max_variable_size);
> -       if (status != EFI_SUCCESS)
> -               return efi_status_to_err(status);
> -
>         /*
>          * This is not a normal filesystem, so no point in pretending it has a block
>          * size; we declare f_bsize to 1, so that we can then report the exact value
> @@ -44,10 +39,19 @@ static int efivarfs_statfs(struct dentry *dentry, struct kstatfs *buf)
>          */
>         buf->f_bsize    = 1;
>         buf->f_namelen  = NAME_MAX;
> -       buf->f_blocks   = storage_space;
> -       buf->f_bfree    = remaining_space;
>         buf->f_type     = dentry->d_sb->s_magic;
>
> +       /* Some UEFI firmware does not implement QueryVariable() */
> +       if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO)) {
> +               status = efivar_query_variable_info(attr, &storage_space,
> +                                                   &remaining_space,
> +                                                   &max_variable_size);
> +               if (status == EFI_SUCCESS) {
> +                       buf->f_blocks   = storage_space;
> +                       buf->f_bfree    = remaining_space;
> +               }
> +       }
> +

I'd prefer not to ignore the error completely here. How about we do

--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -32,10 +32,15 @@ static int efivarfs_statfs(struct dentry *dentry,
struct kstatfs *buf)
        u64 storage_space, remaining_space, max_variable_size;
        efi_status_t status;

-       status = efivar_query_variable_info(attr, &storage_space,
&remaining_space,
-                                           &max_variable_size);
-       if (status != EFI_SUCCESS)
-               return efi_status_to_err(status);
+       /* Some UEFI firmware does not implement QueryVariableInfo() */
+       storage_space = remaining_space = 0;
+       if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO)) {
+               status = efivar_query_variable_info(attr, &storage_space,
+                                                   &remaining_space,
+                                                   &max_variable_size);
+               if (status != EFI_SUCCESS && status != EFI_UNSUPPORTED)
+                       return efi_status_to_err(status);
+       }

        /*
         * This is not a normal filesystem, so no point in pretending
it has a block

(no need to resend if you agree)