linux-hardening - Re: [PATCH v2 1/2] media: staging/intel-ipu3: css: Fix wrong size comparison

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Date:   Mon, 2 Aug 2021 08:46:20 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Yong Zhi <yong.zhi@...el.com>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Tianshu Qiu <tian.shu.qiu@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-hardening@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH v2 1/2] media: staging/intel-ipu3: css: Fix wrong size
 comparison

Hi Sakari,

On 8/2/21 01:05, Sakari Ailus wrote:
> Hi Gustavo,
> 
> I missed you already had sent v2...
> 
> On Fri, Jul 30, 2021 at 07:08:13AM -0500, Gustavo A. R. Silva wrote:
>> There is a wrong comparison of the total size of the loaded firmware
>> css->fw->size with the size of a pointer to struct imgu_fw_header.
>>
>> Fix this by using the right operand 'struct imgu_fw_header' for
>> sizeof, instead of 'struct imgu_fw_header *' and turn binary_header
>> into a flexible-array member. Also, adjust the relational operator
>> to be '<=' instead of '<', as it seems that the intention of the
>> comparison is to determine if the loaded firmware contains any
>> 'struct imgu_fw_info' items in the binary_header[] array than merely
>> the file_header (struct imgu_fw_bi_file_h).
>>
>> The replacement of the one-element array with a flexible-array member
>> also help with the ongoing efforts to globally enable -Warray-bounds
>> and get us closer to being able to tighten the FORTIFY_SOURCE routines
>> on memcpy().
>>
>> Link: https://github.com/KSPP/linux/issues/79
>> Link: https://github.com/KSPP/linux/issues/109
>> Fixes: 09d290f0ba21 ("media: staging/intel-ipu3: css: Add support for firmware management")
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>> ---
>>
>> It'd be just great if someone that knows this code better can confirm
>> these changes are correct. In particular the adjustment of the
>> relational operator. Thanks!
>>
>> Changes in v2:
>>  - Use flexible array and adjust relational operator, accordingly.
> 
> The operator was just correct. The check is just there to see the firmware
> is at least as large as the struct as which it is being accessed.

I'm a bit confused, so based on your reply to v1 of this series, this patch
is now correct, right?

The operator in v1 _was_ correct as long as the one-element array wasn't
transformed into a flexible array, right?

Notice that generally speaking flexible-array members don't occupy space in the
containing structure:

$ pahole -C imgu_fw_header drivers/staging/media/ipu3/ipu3-css-fw.o
struct imgu_fw_header {
	struct imgu_fw_bi_file_h   file_header;          /*     0    72 */
	/* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
	struct imgu_fw_info        binary_header[] __attribute__((__aligned__(8))); /*    72     0 */

	/* size: 72, cachelines: 2, members: 2 */
	/* forced alignments: 1 */
	/* last cacheline: 8 bytes */
} __attribute__((__aligned__(8)));

$ pahole -C imgu_fw_header drivers/staging/media/ipu3/ipu3-css-fw.o
struct imgu_fw_header {
	struct imgu_fw_bi_file_h   file_header;          /*     0    72 */
	/* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
	struct imgu_fw_info        binary_header[1] __attribute__((__aligned__(8))); /*    72  1200 */

	/* size: 1272, cachelines: 20, members: 2 */
	/* forced alignments: 1 */
	/* last cacheline: 56 bytes */
} __attribute__((__aligned__(8)));

So, now that the flexible array transformation is included in the same patch as the
bugfix, the operator is changed from '<' to '<='

Can you please confirm if this v2 is now correct? if so, it'd be great to have your
Reviewed-by tag. :)

Thanks!
--
Gustavo

> 
>>  - Update changelog text.
>>
>>  drivers/staging/media/ipu3/ipu3-css-fw.c | 2 +-
>>  drivers/staging/media/ipu3/ipu3-css-fw.h | 2 +-
>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/media/ipu3/ipu3-css-fw.c b/drivers/staging/media/ipu3/ipu3-css-fw.c
>> index 45aff76198e2..630cb5186b48 100644
>> --- a/drivers/staging/media/ipu3/ipu3-css-fw.c
>> +++ b/drivers/staging/media/ipu3/ipu3-css-fw.c
>> @@ -124,7 +124,7 @@ int imgu_css_fw_init(struct imgu_css *css)
>>  	/* Check and display fw header info */
>>  
>>  	css->fwp = (struct imgu_fw_header *)css->fw->data;
>> -	if (css->fw->size < sizeof(struct imgu_fw_header *) ||
>> +	if (css->fw->size <= sizeof(struct imgu_fw_header) ||
>>  	    css->fwp->file_header.h_size != sizeof(struct imgu_fw_bi_file_h))
>>  		goto bad_fw;
>>  	if (sizeof(struct imgu_fw_bi_file_h) +
>> diff --git a/drivers/staging/media/ipu3/ipu3-css-fw.h b/drivers/staging/media/ipu3/ipu3-css-fw.h
>> index 3c078f15a295..c0bc57fd678a 100644
>> --- a/drivers/staging/media/ipu3/ipu3-css-fw.h
>> +++ b/drivers/staging/media/ipu3/ipu3-css-fw.h
>> @@ -171,7 +171,7 @@ struct imgu_fw_bi_file_h {
>>  
>>  struct imgu_fw_header {
>>  	struct imgu_fw_bi_file_h file_header;
>> -	struct imgu_fw_info binary_header[1];	/* binary_nr items */
>> +	struct imgu_fw_info binary_header[];	/* binary_nr items */
>>  };
>>  
>>  /******************* Firmware functions *******************/
>