lkdtm/usercopy: Adjust test to include an offset to check reporting

Instead of doubling the size, push the start position up by 16 bytes to
still trigger an overflow. This allows to verify that offset reporting
is working correctly.

Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/drivers/misc/lkdtm_usercopy.c b/drivers/misc/lkdtm_usercopy.c
index a64372cc148dbd67951a2cf94611cc39081b3a2f..9ebbb031e5e3998783136fe1e5379cf9c0a20823 100644 (file)
--- a/drivers/misc/lkdtm_usercopy.c
+++ b/drivers/misc/lkdtm_usercopy.c
@@ -119,6 +119,8 @@ static void do_usercopy_heap_size(bool to_user)
 {
        unsigned long user_addr;
        unsigned char *one, *two;
+       void __user *test_user_addr;
+       void *test_kern_addr;
        size_t size = unconst + 1024;
 
        one = kmalloc(size, GFP_KERNEL);
@@ -139,27 +141,30 @@ static void do_usercopy_heap_size(bool to_user)
        memset(one, 'A', size);
        memset(two, 'B', size);
 
+       test_user_addr = (void __user *)(user_addr + 16);
+       test_kern_addr = one + 16;
+
        if (to_user) {
                pr_info("attempting good copy_to_user of correct size\n");
-               if (copy_to_user((void __user *)user_addr, one, size)) {
+               if (copy_to_user(test_user_addr, test_kern_addr, size / 2)) {
                        pr_warn("copy_to_user failed unexpectedly?!\n");
                        goto free_user;
                }
 
                pr_info("attempting bad copy_to_user of too large size\n");
-               if (copy_to_user((void __user *)user_addr, one, 2 * size)) {
+               if (copy_to_user(test_user_addr, test_kern_addr, size)) {
                        pr_warn("copy_to_user failed, but lacked Oops\n");
                        goto free_user;
                }
        } else {
                pr_info("attempting good copy_from_user of correct size\n");
-               if (copy_from_user(one, (void __user *)user_addr, size)) {
+               if (copy_from_user(test_kern_addr, test_user_addr, size / 2)) {
                        pr_warn("copy_from_user failed unexpectedly?!\n");
                        goto free_user;
                }
 
                pr_info("attempting bad copy_from_user of too large size\n");
-               if (copy_from_user(one, (void __user *)user_addr, 2 * size)) {
+               if (copy_from_user(test_kern_addr, test_user_addr, size)) {
                        pr_warn("copy_from_user failed, but lacked Oops\n");
                        goto free_user;
                }