linux-kernel - Re: [PATCH] efivarfs: fix abnormal GUID in variable name by using strcpy to replace null with dash

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Date:	Fri, 01 Mar 2013 16:31:33 +0000
From:	Matt Fleming <matt@...sole-pimps.org>
To:	"Lee, Chun-Yi" <joeyli.kernel@...il.com>
Cc:	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michael Schroeder <mls@...e.com>,
	Josh Boyer <jwboyer@...hat.com>,
	"Lee, Chun-Yi" <jlee@...e.com>, Peter Jones <pjones@...hat.com>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [PATCH] efivarfs: fix abnormal GUID in variable name by using
 strcpy to replace null with dash

On Fri, 2013-03-01 at 15:17 +0000, Matt Fleming wrote:
> On Fri, 2013-03-01 at 11:20 +0800, Lee, Chun-Yi wrote:
> > From: Michael Schroeder <mls@...e.com>
> > 
> > On HP z220 system (firmware version 1.54), some EFI variables are incorrectly
> > named :
> > 
> > ls -d /sys/firmware/efi/vars/*8be4d* | grep -v -- -8be returns
> > /sys/firmware/efi/vars/dbxDefault-pport8be4df61-93ca-11d2-aa0d-00e098032b8c
> > /sys/firmware/efi/vars/KEKDefault-pport8be4df61-93ca-11d2-aa0d-00e098032b8c
> > /sys/firmware/efi/vars/SecureBoot-pport8be4df61-93ca-11d2-aa0d-00e098032b8c
> > /sys/firmware/efi/vars/SetupMode-Information8be4df61-93ca-11d2-aa0d-00e098032b8c
> > 
> > That causes by the following statement in efivar_create_sysfs_entry function:
> > 
> >  *(short_name + strlen(short_name)) = '-';
> > efi_guid_unparse(vendor_guid, short_name + strlen(short_name));
> > 
> > The trailing \0 is overwritten with '-', but the next char doesn't seem to be a \0
> > as well for HP. So, the second strlen return the point of next '\0', causes there
> > have garbage string attached before GUID.
> > 
> > Tested on On HP z220.
> 
> What's more likely happening here is that GetNextVariable() is broken on
> this HP firmware and variable_name_size is too big for the given
> variable in variable_name. We've seen other reports of similar bugs,
> 
> 	https://bugzilla.kernel.org/show_bug.cgi?id=47631
> 
> 
> Could someone try this patch against Linus' tree?

Urgh, and here's a version that isn't utterly, utterly broken...

---

>From 4b2ef72bca72039717efe4570ec858a86d565b34 Mon Sep 17 00:00:00 2001
From: Matt Fleming <matt.fleming@...el.com>
Date: Fri, 1 Mar 2013 14:49:12 +0000
Subject: [PATCH] efivars: Sanitise string length returned by
 GetNextVariableName()

Some buggy firmware implementations return a string length from
GetNextVariableName() that is actually larger than the string in
'variable_name', as Michael Schroeder writes,

  > On HP z220 system (firmware version 1.54), some EFI variables are
  > incorrectly named :
  >
  > ls -d /sys/firmware/efi/vars/*8be4d* | grep -v -- -8be returns
  > /sys/firmware/efi/vars/dbxDefault-pport8be4df61-93ca-11d2-aa0d-00e098032b8c
  > /sys/firmware/efi/vars/KEKDefault-pport8be4df61-93ca-11d2-aa0d-00e098032b8c
  > /sys/firmware/efi/vars/SecureBoot-pport8be4df61-93ca-11d2-aa0d-00e098032b8c
  > /sys/firmware/efi/vars/SetupMode-Information8be4df61-93ca-11d2-aa0d-00e098032b8c

Since 'variable_name' is a string, we can validate its size by
searching for the terminating NULL character.

Reported-by: Frederic Crozat <fcrozat@...e.com>
Cc: Matthew Garrett <mjg59@...f.ucam.org>
Cc: Josh Boyer <jwboyer@...hat.com>
Cc: Michael Schroeder <mls@...e.com>
Cc: Lee, Chun-Yi <jlee@...e.com>
Cc: Lingzhu Xiang <lxiang@...hat.com>
Signed-off-by: Matt Fleming <matt.fleming@...el.com>
---
 drivers/firmware/efivars.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 7320bf8..ab477b8 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -1895,6 +1895,33 @@ void unregister_efivars(struct efivars *efivars)
 }
 EXPORT_SYMBOL_GPL(unregister_efivars);
 
+/*
+ * Sanity check size of a variable name.
+ */
+static unsigned long sanity_check_size(efi_char16_t *variable_name,
+				       unsigned long variable_name_size)
+{
+	unsigned long len;
+	efi_char16_t c;
+
+	/*
+	 * The variable name is, by definition, a NULL-terminated
+	 * string, so make absolutely sure that variable_name_size is
+	 * the value we expect it to be. If not, return the real size.
+	 */
+	for (len = 2; len <= variable_name_size; len += sizeof(c)) {
+		c = variable_name[(len / sizeof(c)) - 1];
+		if (!c)
+			break;
+	}
+
+
+	if (len != variable_name_size)
+		printk(KERN_WARNING "efivars: bogus variable_name_size: %lu %lu\n", len, variable_name_size);
+
+	return min(len, variable_name_size);
+}
+
 int register_efivars(struct efivars *efivars,
 		     const struct efivar_operations *ops,
 		     struct kobject *parent_kobj)
@@ -1941,8 +1968,11 @@ int register_efivars(struct efivars *efivars,
 		status = ops->get_next_variable(&variable_name_size,
 						variable_name,
 						&vendor_guid);
+
 		switch (status) {
 		case EFI_SUCCESS:
+			variable_name_size = sanity_check_size(variable_name,
+							       variable_name_size);
 			efivar_create_sysfs_entry(efivars,
 						  variable_name_size,
 						  variable_name,
-- 
1.7.11.7



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