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

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Date:	Sat, 02 Mar 2013 07:41:39 +0800
From:	joeyli <jlee@...e.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michael Schroeder <mls@...e.com>,
	Josh Boyer <jwboyer@...hat.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

於 五，2013-03-01 於 16:31 +0000，Matt Fleming 提到：
> 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...

Thanks for Matt's patch, we will try it!

Joey Lee

> 
> ---
> 
> >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,


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