[PATCH v3 1/8] efi: efivars: don't crash in efivar_set_variable{,_locked} in r/o case

[Dmitry Baryshkov]

If efivar implementation doesn't provide write support, then calling
efivar_set_variable() (e.g. when PM8xxx RTC driver tries to update the
RTC offset) will crash the system. Prevent that by checking that
set_variable callback is actually provided and fail with an
EFI_WRITE_PROTECTED if it is not.

Fixes: 472831d4c4b2 ("efi: vars: Add thin wrapper around EFI get/set variable interface")
Reported-by: Johan Hovold <johan@xxxxxxxxxx>
Closes: https://lore.kernel.org/r/aFlps9iUcD42vN4w@xxxxxxxxxxxxxxxxxxxx
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
---
 drivers/firmware/efi/vars.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 3700e98697676d8e6f04f061f447391503f9abba..11c5f785c09364f61642d82416822cb2e1a027fd 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -227,6 +227,8 @@ efi_status_t efivar_set_variable_locked(efi_char16_t *name, efi_guid_t *vendor,
 	setvar = __efivars->ops->set_variable_nonblocking;
 	if (!setvar || !nonblocking)
 		 setvar = __efivars->ops->set_variable;
+	if (!setvar)
+		return EFI_WRITE_PROTECTED;
 
 	return setvar(name, vendor, attr, data_size, data);
 }

-- 
2.39.5