lkdtm: Add READ_AFTER_FREE test
In a similar manner to WRITE_AFTER_FREE, add a READ_AFTER_FREE
test to test free poisoning features. Sample output when
no sanitization is present:
# echo READ_AFTER_FREE > /sys/kernel/debug/provoke-crash/DIRECT
[ 17.542473] lkdtm: Performing direct entry READ_AFTER_FREE
[ 17.543866] lkdtm: Value in memory before free: 12345678
[ 17.545212] lkdtm: Attempting bad read from freed memory
[ 17.546542] lkdtm: Memory was not poisoned
with slub_debug=P:
# echo READ_AFTER_FREE > /sys/kernel/debug/provoke-crash/DIRECT
[ 22.415531] lkdtm: Performing direct entry READ_AFTER_FREE
[ 22.416366] lkdtm: Value in memory before free: 12345678
[ 22.417137] lkdtm: Attempting bad read from freed memory
[ 22.417897] lkdtm: Memory correctly poisoned, calling BUG
Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
index 11fdadc..8de4746 100644
--- a/drivers/misc/lkdtm.c
+++ b/drivers/misc/lkdtm.c
@@ -92,6 +92,7 @@
CT_UNALIGNED_LOAD_STORE_WRITE,
CT_OVERWRITE_ALLOCATION,
CT_WRITE_AFTER_FREE,
+ CT_READ_AFTER_FREE,
CT_SOFTLOCKUP,
CT_HARDLOCKUP,
CT_SPINLOCKUP,
@@ -129,6 +130,7 @@
"UNALIGNED_LOAD_STORE_WRITE",
"OVERWRITE_ALLOCATION",
"WRITE_AFTER_FREE",
+ "READ_AFTER_FREE",
"SOFTLOCKUP",
"HARDLOCKUP",
"SPINLOCKUP",
@@ -417,6 +419,42 @@
memset(data, 0x78, len);
break;
}
+ case CT_READ_AFTER_FREE: {
+ 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(*base)) / 2;
+
+ base = kmalloc(len, GFP_KERNEL);
+ if (!base)
+ break;
+
+ val = kmalloc(len, GFP_KERNEL);
+ if (!val)
+ break;
+
+ *val = 0x12345678;
+ base[offset] = *val;
+ pr_info("Value in memory before free: %x\n", base[offset]);
+
+ kfree(base);
+
+ 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;
+ }
case CT_SOFTLOCKUP:
preempt_disable();
for (;;)