ethtool: fix ethnl_bitmap32_not_zero() bit interval semantics

[ Upstream commit 3d042592eb ]

ethnl_bitmap32_not_zero() should return true if some bit in [start, end)
is set:

- Fix inverted memchr_inv() sense: return true when the scan finds a
  non-zero byte, not when the middle words are all zero.
- Return false for an empty interval (end <= start).
- When end is 32-bit aligned, indices in [start, end) do not include any
  bits from map[end_word]; return false after earlier checks found no
  non-zero data.

Fixes: 10b518d4e6 ("ethtool: netlink bitset handling")
Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/ethtool/bitset.c

@@ -91,7 +91,7 @@ static bool ethnl_bitmap32_not_zero(const u32 *map, unsigned int start,
 	u32 mask;
 
 	if (end <= start)
-		return true;
+		return false;
 
 	if (start % 32) {
 		mask = ethnl_upper_bits(start);
@@ -104,11 +104,11 @@ static bool ethnl_bitmap32_not_zero(const u32 *map, unsigned int start,
 		start_word++;
 	}
 
-	if (!memchr_inv(map + start_word, '\0',
-			(end_word - start_word) * sizeof(u32)))
+	if (memchr_inv(map + start_word, '\0',
+		       (end_word - start_word) * sizeof(u32)))
 		return true;
 	if (end % 32 == 0)
-		return true;
+		return false;
 	return map[end_word] & ethnl_lower_bits(end);
 }