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

[Ard Biesheuvel]

On Sun, 10 Sept 2023 at 15:08, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Sun, 10 Sept 2023 at 06:53, Heinrich Schuchardt
> <heinrich.schuchardt@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > ---
> > 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)

Actually, perhaps it would be better to simply fall back to the old
logic if QueryVariableInfo is not provided:

diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index e028fafa04f3..50b05f1fa974 100644
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -30,10 +30,15 @@ static int efivarfs_statfs(struct dentry *dentry,
struct kstatfs *buf)
                         EFI_VARIABLE_BOOTSERVICE_ACCESS |
                         EFI_VARIABLE_RUNTIME_ACCESS;
        u64 storage_space, remaining_space, max_variable_size;
-       efi_status_t status;
+       efi_status_t status = EFI_UNSUPPORTED;
+
+       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_UNSUPPORTED)
+               return simple_statfs(dentry, buf);

-       status = efivar_query_variable_info(attr, &storage_space,
&remaining_space,
-                                           &max_variable_size);
        if (status != EFI_SUCCESS)
                return efi_status_to_err(status);