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Message-ID: <20160224232730.GA5113@www.outflux.net>
Date: Wed, 24 Feb 2016 15:27:30 -0800
From: Kees Cook <keescook@...omium.org>
To: Laura Abbott <labbott@...oraproject.org>
Cc: Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
kernel-hardening@...ts.openwall.com,
LKML <linux-kernel@...r.kernel.org>
Subject: [RFC][PATCH] lkdtm: improve use-after-free tests
This fixes a typo in the CT_READ_AFTER_FREE test (*tmp was triggering a GP),
moves the CT_WRITE_AFTER_FREE test to the middle to better test poisoning
instead of free list checks. Also reorders/clarifies some pr_info calls
and validates poisoning.
Signed-off-by: Kees Cook <keescook@...omium.org>
---
This applies on top of the "[PATCH 0/2] LKDTM test updates" and should
probably just get broken out into the separate patches.
---
drivers/misc/lkdtm.c | 61 ++++++++++++++++++++++++++++++++++------------------
1 file changed, 40 insertions(+), 21 deletions(-)
diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
index 41213bb7a58c..69a3714ff55c 100644
--- a/drivers/misc/lkdtm.c
+++ b/drivers/misc/lkdtm.c
@@ -415,24 +415,33 @@ static void lkdtm_do_action(enum ctype which)
break;
}
case CT_WRITE_AFTER_FREE: {
+ int *base;
size_t len = 1024;
- u32 *data = kmalloc(len, GFP_KERNEL);
+ /*
+ * The slub allocator uses the first word to store the free
+ * pointer in some configurations. Use the middle of the
+ * allocation to avoid running into the freelist
+ */
+ size_t offset = (len / sizeof(*base)) / 2;
+
+ base = kmalloc(len, GFP_KERNEL);
+ pr_info("Allocated memory %p-%p\n", base, &base[offset * 2]);
+ kfree(base);
+ pr_info("Attempting bad write to freed memory at %p\n",
+ &base[offset]);
+ base[offset] = 0x0abcdef0;
- kfree(data);
- schedule();
- memset(data, 0x78, len);
break;
}
case CT_READ_AFTER_FREE: {
- int **base;
- int *val, *tmp;
+ int *base, *val, saw;
size_t len = 1024;
/*
* The slub allocator uses the first word to store the free
* pointer in some configurations. Use the middle of the
* allocation to avoid running into the freelist
*/
- size_t offset = (len/sizeof(int *))/2;
+ size_t offset = (len / sizeof(*base)) / 2;
base = kmalloc(len, GFP_KERNEL);
if (!base)
@@ -443,14 +452,19 @@ static void lkdtm_do_action(enum ctype which)
break;
*val = 0x12345678;
- pr_info("Value in memory before free: %x\n", *val);
+ base[offset] = *val;
+ pr_info("Value in memory before free: %x\n", base[offset]);
- base[offset] = val;
kfree(base);
- tmp = base[offset];
- pr_info("Attempting to read from freed memory\n");
- pr_info("Successfully read value: %x\n", *tmp);
+ pr_info("Attempting bad read from freed memory\n");
+ saw = base[offset];
+ if (saw != *val) {
+ /* Good! Poisoning happened, so declare a win. */
+ pr_info("Memory correctly poisoned, calling BUG\n");
+ BUG();
+ }
+ pr_info("Memory was not poisoned\n");
kfree(val);
break;
@@ -463,15 +477,14 @@ static void lkdtm_do_action(enum ctype which)
memset((void *)p, 0x3, PAGE_SIZE);
free_page(p);
schedule();
- pr_info("Writing to the buddy page after free\n");
+ pr_info("Attempting bad write to the buddy page after free\n");
memset((void *)p, 0x78, PAGE_SIZE);
- pr_info("Wrote to free page successfully\n");
break;
}
case CT_READ_BUDDY_AFTER_FREE: {
unsigned long p = __get_free_page(GFP_KERNEL);
- int *tmp, *val = kmalloc(1024, GFP_KERNEL);
- int **base;
+ int saw, *val = kmalloc(1024, GFP_KERNEL);
+ int *base;
if (!p)
break;
@@ -479,15 +492,21 @@ static void lkdtm_do_action(enum ctype which)
if (!val)
break;
- base = (int **)p;
+ base = (int *)p;
*val = 0x12345678;
- pr_info("Value in memory before free: %x\n", *val);
- base[0] = val;
+ base[0] = *val;
+ pr_info("Value in memory before free: %x\n", base[0]);
free_page(p);
- tmp = base[0];
pr_info("Attempting to read from freed memory\n");
- pr_info("Successfully read value: %x\n", *tmp);
+ saw = base[0];
+ if (saw != *val) {
+ /* Good! Poisoning happened, so declare a win. */
+ pr_info("Buddy page correctly poisoned, calling BUG\n");
+ BUG();
+ }
+ pr_info("Buddy page was not poisoned\n");
+
kfree(val);
break;
}
--
2.6.3
--
Kees Cook
Chrome OS & Brillo Security
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