linux-hardening - [PATCH] lkdtm/heap: Avoid __alloc

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Date:   Tue, 17 Aug 2021 21:45:40 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] lkdtm/heap: Avoid __alloc_size hint warning

Once __alloc_size hints have been added, the compiler will
(correctly!) see this as an overflow. We are, however, trying to test
for this condition, so work around it with a volatile int.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/misc/lkdtm/heap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c
index 3d9aae5821a0..e59fcbe00ae0 100644
--- a/drivers/misc/lkdtm/heap.c
+++ b/drivers/misc/lkdtm/heap.c
@@ -12,6 +12,8 @@ static struct kmem_cache *double_free_cache;
 static struct kmem_cache *a_cache;
 static struct kmem_cache *b_cache;
 
+static volatile int __offset = 1;
+
 /*
  * If there aren't guard pages, it's likely that a consecutive allocation will
  * let us overflow into the second allocation without overwriting something real.
@@ -24,7 +26,7 @@ void lkdtm_VMALLOC_LINEAR_OVERFLOW(void)
 	two = vzalloc(PAGE_SIZE);
 
 	pr_info("Attempting vmalloc linear overflow ...\n");
-	memset(one, 0xAA, PAGE_SIZE + 1);
+	memset(one, 0xAA, PAGE_SIZE + __offset);
 
 	vfree(two);
 	vfree(one);
-- 
2.30.2