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

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Date:   Thu,  5 Jan 2023 14:05:54 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Helge Deller <deller@....de>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Yangxi Xiang <xyangxi5@...il.com>,
        Xuezhi Zhang <zhangxuezhi1@...lpad.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] vt: Replace 0-length array with flexible array

Zero-length arrays are deprecated[1]. Replace struct uni_screen's
"lines" 0-length array with a flexible array. Detected with GCC 13,
using -fstrict-flex-arrays=3:

../drivers/tty/vt/vt.c: In function 'vc_uniscr_copy_area':
../drivers/tty/vt/vt.c:488:48: warning: array subscript dst_row is outside array bounds of 'char32_t *[0]' {aka 'unsigned int *[]'} [-Warray-bounds=]
  488 |                 char32_t *dst_line = dst->lines[dst_row];
      |                                      ~~~~~~~~~~^~~~~~~~~
../drivers/tty/vt/vt.c:335:19: note: while referencing 'lines'
  335 |         char32_t *lines[0];
      |                   ^~~~~

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

Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jirislaby@...nel.org>
Cc: Daniel Vetter <daniel.vetter@...ll.ch>
Cc: "Ilpo Järvinen" <ilpo.jarvinen@...ux.intel.com>
Cc: Helge Deller <deller@....de>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/tty/vt/vt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 981d2bfcf9a5..b1445f00f616 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -332,7 +332,7 @@ typedef uint32_t char32_t;
  * scrolling only implies some pointer shuffling.
  */
 struct uni_screen {
-	char32_t *lines[0];
+	DECLARE_FLEX_ARRAY(char32_t *, lines);
 };
 
 static struct uni_screen *vc_uniscr_alloc(unsigned int cols, unsigned int rows)
-- 
2.34.1