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

[Compostella, Jeremy]

 Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> writes:

> On Fri, 29 Apr, at 03:53:39PM, Jeremy Compostella wrote:
>> 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;
>> +	}
>
> This isn't right. The usual return value for this scenario would be
> either -ENOMEM or -EINVAL. Personally I'd lean towards -EINVAL.
Right. Done.

>>  
>> -	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;
>> +	}
>
> This should be -ENOMEM.
Done.

>>  
>> -	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);
>
> You need to check this return value too now.
We are leaving this function returning NOTIFY_DONE whatever the return
value of that last efibc_set_variable() call.

Please find the updated patch in attachment.

Also, thank you for answering Ard's questions.  I promised I won't
look at my emails on Labor day ;)

JÃrÃmy