linux-hardening - [PATCH] media: atomisp: Perform a single memset() for union

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Date:   Sun, 11 Jul 2021 07:51:01 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Martiros Shakhzadyan <vrzh@...h.net>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: [PATCH] media: atomisp: Perform a single memset() for union

There is no need to memset() both dvs_grid_info and dvs_stat_grid_info
separately: they are part of the same union. Instead, just zero the
union itself. This additionally avoids a false positive (due to a
gcc optimization bug[1]) when building with the coming FORTIFY_SOURCE
improvements:

In function 'fortify_memset_chk',
    inlined from 'sh_css_pipe_get_grid_info' at drivers/staging/media/atomisp/pci/sh_css.c:5186:3,
    inlined from 'ia_css_stream_create' at drivers/staging/media/atomisp/pci/sh_css.c:9442:10:
./include/linux/fortify-string.h:199:4: warning: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribute-warning]
  199 |    __write_overflow_field();
      |    ^~~~~~~~~~~~~~~~~~~~~~~~

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101419

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/staging/media/atomisp/pci/sh_css.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/staging/media/atomisp/pci/sh_css.c b/drivers/staging/media/atomisp/pci/sh_css.c
index d26b1301eeb7..ffa7f8a88a70 100644
--- a/drivers/staging/media/atomisp/pci/sh_css.c
+++ b/drivers/staging/media/atomisp/pci/sh_css.c
@@ -5181,10 +5181,7 @@ sh_css_pipe_get_grid_info(struct ia_css_pipe *pipe,
 		ia_css_binary_dvs_grid_info(binary, info, pipe);
 		ia_css_binary_dvs_stat_grid_info(binary, info, pipe);
 	} else {
-		memset(&info->dvs_grid.dvs_grid_info, 0,
-		       sizeof(info->dvs_grid.dvs_grid_info));
-		memset(&info->dvs_grid.dvs_stat_grid_info, 0,
-		       sizeof(info->dvs_grid.dvs_stat_grid_info));
+		memset(&info->dvs_grid, 0, sizeof(info->dvs_grid));
 	}
 
 	if (binary) {
-- 
2.30.2