[PATCH 3.16.y-ckt 140/142] efi: Add pstore variables to the deletion whitelist

[Luis Henriques]

3.16.7-ckt26 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Matt Fleming <matt at codeblueprint.co.uk>

commit e246eb568bc4cbbdd8a30a3c11151ff9b7ca7312 upstream.

Laszlo explains why this is a good idea,

 'This is because the pstore filesystem can be backed by UEFI variables,
  and (for example) a crash might dump the last kilobytes of the dmesg
  into a number of pstore entries, each entry backed by a separate UEFI
  variable in the above GUID namespace, and with a variable name
  according to the above pattern.

  Please see "drivers/firmware/efi/efi-pstore.c".

  While this patch series will not prevent the user from deleting those
  UEFI variables via the pstore filesystem (i.e., deleting a pstore fs
  entry will continue to delete the backing UEFI variable), I think it
  would be nice to preserve the possibility for the sysadmin to delete
  Linux-created UEFI variables that carry portions of the crash log,
  *without* having to mount the pstore filesystem.'

There's also no chance of causing machines to become bricked by
deleting these variables, which is the whole purpose of excluding
things from the whitelist.

Use the LINUX_EFI_CRASH_GUID guid and a wildcard '*' for the match so
that we don't have to update the string in the future if new variable
name formats are created for crash dump variables.

Reported-by: Laszlo Ersek <lersek at redhat.com>
Acked-by: Peter Jones <pjones at redhat.com>
Tested-by: Peter Jones <pjones at redhat.com>
Cc: Matthew Garrett <mjg59 at srcf.ucam.org>
Cc: "Lee, Chun-Yi" <jlee at suse.com>
Signed-off-by: Matt Fleming <matt at codeblueprint.co.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/firmware/efi/vars.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index ab68e57172aa..4e2f46938bf0 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -198,6 +198,7 @@ static const struct variable_validate variable_validate[] = {
 	{ EFI_GLOBAL_VARIABLE_GUID, "OsIndications", NULL },
 	{ EFI_GLOBAL_VARIABLE_GUID, "PlatformLang", validate_ascii_string },
 	{ EFI_GLOBAL_VARIABLE_GUID, "Timeout", validate_uint16 },
+	{ LINUX_EFI_CRASH_GUID, "*", NULL },
 	{ NULL_GUID, "", NULL },
 };