Re: [tip:efi/core] efibc: Add EFI Bootloader Control module

[jeremy.compostella@xxxxxxxxx (Compostella, Jeremy)]

Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> writes:

> On Fri, 29 Apr, at 01:36:01PM, Jeremy Compostella wrote:
>> I would go for this last proposal because it fixes the issue, it works
>> with the potential race condition you mentioned and it is a simple
>> solution.  Yet, it means that if we really run into a race condition,
>> the LoaderEntryOneShot value might be indeterminate.
>> 
>> Though, this is a very unlikely situation and if it happens I cannot
>> think of any good reason to prefer to store the first restart target
>> or the second.
>> 
>> Do you want me to make this change ?
>
> Yes please, that'd be greatly appreciated. Be sure to do it on top of
> either the EFI 'next' branch or tip:efi/core.
Please, find the patch in attachment.  I wrote it on top of
tip:efi/core.

>From ef3a2941769e59b11d1ec36117209dc4c90c7cf9 Mon Sep 17 00:00:00 2001
From: Jeremy Compostella <jeremy.compostella@xxxxxxxxx>
Date: Fri, 29 Apr 2016 15:29:59 +0200
Subject: [PATCH] efibc: fix excessive stack footprint warning

Use dynamic memory allocation instead of stack memory for the entry
object.

This patch also fixes a potential buffer override.

Signed-off-by: Jeremy Compostella <jeremy.compostella@xxxxxxxxx>
---
 drivers/firmware/efi/efibc.c | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/drivers/firmware/efi/efibc.c b/drivers/firmware/efi/efibc.c
index 2e0c7cc..dd6d1a6 100644
--- a/drivers/firmware/efi/efibc.c
+++ b/drivers/firmware/efi/efibc.c
@@ -17,6 +17,7 @@
 #include <linux/efi.h>
 #include <linux/module.h>
 #include <linux/reboot.h>
+#include <linux/slab.h>
 
 static void efibc_str_to_str16(const char *str, efi_char16_t *str16)
 {
@@ -28,42 +29,53 @@ static void efibc_str_to_str16(const char *str, efi_char16_t *str16)
 	str16[i] = '\0';
 }
 
-static void efibc_set_variable(const char *name, const char *value)
+static int efibc_set_variable(const char *name, const char *value)
 {
 	int ret;
 	efi_guid_t guid = LINUX_EFI_LOADER_ENTRY_GUID;
-	struct efivar_entry entry;
+	struct efivar_entry *entry;
 	size_t size = (strlen(value) + 1) * sizeof(efi_char16_t);
 
-	if (size > sizeof(entry.var.Data))
+	if (size > sizeof(entry->var.Data)) {
 		pr_err("value is too large");
+		return -1;
+	}
 
-	efibc_str_to_str16(name, entry.var.VariableName);
-	efibc_str_to_str16(value, (efi_char16_t *)entry.var.Data);
-	memcpy(&entry.var.VendorGuid, &guid, sizeof(guid));
+	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
+	if (!entry) {
+		pr_err("failed to allocate efivar entry");
+		return -1;
+	}
 
-	ret = efivar_entry_set(&entry,
+	efibc_str_to_str16(name, entry->var.VariableName);
+	efibc_str_to_str16(value, (efi_char16_t *)entry->var.Data);
+	memcpy(&entry->var.VendorGuid, &guid, sizeof(guid));
+
+	ret = efivar_entry_set(entry,
 			       EFI_VARIABLE_NON_VOLATILE
 			       | EFI_VARIABLE_BOOTSERVICE_ACCESS
 			       | EFI_VARIABLE_RUNTIME_ACCESS,
-			       size, entry.var.Data, NULL);
+			       size, entry->var.Data, NULL);
 	if (ret)
 		pr_err("failed to set %s EFI variable: 0x%x\n",
 		       name, ret);
+
+	kfree(entry);
+	return ret;
 }
 
 static int efibc_reboot_notifier_call(struct notifier_block *notifier,
 				      unsigned long event, void *data)
 {
 	const char *reason = "shutdown";
+	int ret;
 
 	if (event == SYS_RESTART)
 		reason = "reboot";
 
-	efibc_set_variable("LoaderEntryRebootReason", reason);
-
-	if (!data)
-		return NOTIFY_DONE;
+	ret = efibc_set_variable("LoaderEntryRebootReason", reason);
+	if (ret || !data)
+ 		return NOTIFY_DONE;
 
 	efibc_set_variable("LoaderEntryOneShot", (char *)data);
 
-- 
1.9.1

Jérémy
-- 
One Emacs to rule them all