[patch 088/140] lib/test_bitmap.c: do not accidentally use stack VLA

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From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: lib/test_bitmap.c: do not accidentally use stack VLA

This avoids an accidental stack VLA (since the compiler thinks the value
of "len" can change, even when marked "const").  This just replaces it
with a #define so it will DTRT.

Seen with -Wvla.  Fixed as part of the directive to remove all VLAs from
the kernel: https://lkml.org/lkml/2018/3/7/621

Link: http://lkml.kernel.org/r/20180307212555.GA17927@beast
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 lib/test_bitmap.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff -puN lib/test_bitmap.c~test_bitmap-do-not-accidentally-use-stack-vla lib/test_bitmap.c
--- a/lib/test_bitmap.c~test_bitmap-do-not-accidentally-use-stack-vla
+++ a/lib/test_bitmap.c
@@ -296,15 +296,17 @@ static void __init test_bitmap_parselist
 	}
 }
 
+#define EXP_BYTES	(sizeof(exp) * 8)
+
 static void __init test_bitmap_arr32(void)
 {
-	unsigned int nbits, next_bit, len = sizeof(exp) * 8;
+	unsigned int nbits, next_bit;
 	u32 arr[sizeof(exp) / 4];
-	DECLARE_BITMAP(bmap2, len);
+	DECLARE_BITMAP(bmap2, EXP_BYTES);
 
 	memset(arr, 0xa5, sizeof(arr));
 
-	for (nbits = 0; nbits < len; ++nbits) {
+	for (nbits = 0; nbits < EXP_BYTES; ++nbits) {
 		bitmap_to_arr32(arr, exp, nbits);
 		bitmap_from_arr32(bmap2, arr, nbits);
 		expect_eq_bitmap(bmap2, exp, nbits);
@@ -316,7 +318,7 @@ static void __init test_bitmap_arr32(voi
 				" tail is not safely cleared: %d\n",
 				nbits, next_bit);
 
-		if (nbits < len - 32)
+		if (nbits < EXP_BYTES - 32)
 			expect_eq_uint(arr[DIV_ROUND_UP(nbits, 32)],
 								0xa5a5a5a5);
 	}
_
--
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