linux-hardening - [PATCH] fbdev: Replace 0-length array with flexible array

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Message-Id: <20230105192034.never.249-kees@kernel.org>
Date:   Thu,  5 Jan 2023 11:20:38 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Helge Deller <deller@....de>
Cc:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] fbdev: Replace 0-length array with flexible array

Zero-length arrays are deprecated[1]. Replace struct aperture's "ranges"
0-length array with a flexible array. (How is the size of this array
verified?) Detected with GCC 13, using -fstrict-flex-arrays=3:

samples/vfio-mdev/mdpy-fb.c: In function 'mdpy_fb_probe':
samples/vfio-mdev/mdpy-fb.c:169:32: warning: array subscript 0 is outside array bounds of 'struct aperture[0]' [-Warray-bounds=]
  169 |         info->apertures->ranges[0].base = info->fix.smem_start;
      |         ~~~~~~~~~~~~~~~~~~~~~~~^~~
In file included from samples/vfio-mdev/mdpy-fb.c:21:
include/linux/fb.h:510:19: note: while referencing 'ranges'
  510 |                 } ranges[0];
      |                   ^~~~~~

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays

Cc: Helge Deller <deller@....de>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: linux-fbdev@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/fb.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fb.h b/include/linux/fb.h
index 96b96323e9cb..bf59d6a3590f 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -507,7 +507,7 @@ struct fb_info {
 		struct aperture {
 			resource_size_t base;
 			resource_size_t size;
-		} ranges[0];
+		} ranges[];
 	} *apertures;
 
 	bool skip_vt_switch; /* no VT switch on suspend/resume required */
-- 
2.34.1