kernel/sysctl.c: switch to bitmap_zalloc()

Switch to bitmap_zalloc() to show clearly what we are allocating.
Besides that it returns pointer of bitmap type instead of opaque void *.

Link: http://lkml.kernel.org/r/20190304094037.57756-1-andriy.shevchenko@linux.intel.comSigned-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sysctl.c

@@ -3178,9 +3178,7 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
 		if (IS_ERR(kbuf))
 			return PTR_ERR(kbuf);
 
-		tmp_bitmap = kcalloc(BITS_TO_LONGS(bitmap_len),
-				     sizeof(unsigned long),
-				     GFP_KERNEL);
+		tmp_bitmap = bitmap_zalloc(bitmap_len, GFP_KERNEL);
 		if (!tmp_bitmap) {
 			kfree(kbuf);
 			return -ENOMEM;
@@ -3271,7 +3269,7 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
 		*ppos += *lenp;
 	}
 
-	kfree(tmp_bitmap);
+	bitmap_free(tmp_bitmap);
 	return err;
 }