[PATCH] linux/bitmap.h: fix potential sign-extension overflow

[PATCH] linux/bitmap.h: fix potential sign-extension overflow

[Gustavo A. R. Silva]

In expression 0xff << offset, left shifting by more than 31 bits has
undefined behavior. Notice that the shift amount, *offset*, can be as
much as 63.

Fix this by adding suffix ULL to integer 0xFF.

Addresses-Coverity: 1487071 ("Bad bit shift operation")
Fixes: d33f5cbaadd8 ("bitops: introduce the for_each_set_clump8 macro")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 include/linux/bitmap.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 942871bfe47e..96f91db25b06 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -520,7 +520,7 @@ static inline void bitmap_set_value8(unsigned long *map, unsigned long value,
 	const size_t index = BIT_WORD(start);
 	const unsigned long offset = start % BITS_PER_LONG;
 
-	map[index] &= ~(0xFF << offset);
+	map[index] &= ~(0xFFULL << offset);
 	map[index] |= value << offset;
 }
 
-- 
2.23.0

Re: [PATCH] linux/bitmap.h: fix potential sign-extension overflow

[Joe Perches]

On Tue, 2019-10-15 at 13:46 -0500, Gustavo A. R. Silva wrote:
> In expression 0xff << offset, left shifting by more than 31 bits has
> undefined behavior. Notice that the shift amount, *offset*, can be as
> much as 63.
> 
> Fix this by adding suffix ULL to integer 0xFF.
[]
> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
[]
> @@ -520,7 +520,7 @@ static inline void bitmap_set_value8(unsigned long *map, unsigned long value,
>  	const size_t index = BIT_WORD(start);
>  	const unsigned long offset = start % BITS_PER_LONG;
>  
> -	map[index] &= ~(0xFF << offset);
> +	map[index] &= ~(0xFFULL << offset);

BITS_PER_LONG is 32 and 0xFFULL is 64 bit
when compiled for 32 bit arches.

This should just be 0xFFUL and not ULL.