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Commit 250a8988 authored by Laura Abbott's avatar Laura Abbott Committed by Kees Cook
Browse files

lkdtm: Update WRITE_AFTER_FREE test 



The SLUB allocator may use the first word of a freed block to store the
freelist information. This may make it harder to test poisoning
features. Change the WRITE_AFTER_FREE test to better match what
the READ_AFTER_FREE test does and also print out a big more information.

Signed-off-by: default avatarLaura Abbott <labbott@fedoraproject.org>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent bc0b8cc6

drivers/misc/lkdtm.c

+13 −4
Original line number Original line Diff line number Diff line
@@ -411,12 +411,21 @@ static void lkdtm_do_action(enum ctype which) 
		break;

		break;

	}

	}

	case CT_WRITE_AFTER_FREE: {

	case CT_WRITE_AFTER_FREE: {

		int *base;

		size_t len = 1024;

		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;





		kfree(data);

		base = kmalloc(len, GFP_KERNEL);

		schedule();

		pr_info("Allocated memory %p-%p\n", base, &base[offset * 2]);

		memset(data, 0x78, len);

		kfree(base);

		pr_info("Attempting bad write to freed memory at %p\n",

			&base[offset]);

		base[offset] = 0x0abcdef0;

		break;

		break;

	}

	}

	case CT_READ_AFTER_FREE: {

	case CT_READ_AFTER_FREE: {