test_bitmap: Do not accidentally use stack VLA

PATCH New Kees Cook 1 participant 1 message Mar 7, 2018

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Kees Cook

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2018-03-07 21:25 UTC #0 lore raw

PATCH 1/1 test_bitmap: 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

Cc Yury Norov <[email protected]>

Cc Andy Shevchenko <[email protected]>

Cc Matthew Wilcox <[email protected]>

Signed-off-by Kees Cook <[email protected]>

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

lib/test_bitmap.c +6 -4

index b3f235baa05d..756f20ad03db 100644
@@ -292,15 +292,17 @@ static void __init test_bitmap_parselist(void)
 	}
 }
 
+#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);

@@ -312,7 +314,7 @@ static void __init test_bitmap_arr32(void)
 				" 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);
 	}

Signature · 6 lines

2.7.4


-- 
Kees Cook
Pixel Security