From: Nirjhar Roy <nirjhar@xxxxxxxxxxxxx>
Faults from copy_from_kernel_nofault() needs to be handled by fixup
table and should not be handled by kfence. Otherwise while reading
/proc/kcore which uses copy_from_kernel_nofault(), kfence can generate
false negatives. This can happen when /proc/kcore ends up reading an
unmapped address from kfence pool.
Let's add a testcase to cover this case.
Co-developed-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
Signed-off-by: Nirjhar Roy <nirjhar@xxxxxxxxxxxxx>
Cc: kasan-dev@xxxxxxxxxxxxxxxx
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
---
mm/kfence/kfence_test.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
index 00fd17285285..f65fb182466d 100644
--- a/mm/kfence/kfence_test.c
+++ b/mm/kfence/kfence_test.c
@@ -383,6 +383,22 @@ static void test_use_after_free_read(struct kunit *test)
KUNIT_EXPECT_TRUE(test, report_matches(&expect));
}
+static void test_use_after_free_read_nofault(struct kunit *test)
+{
+ const size_t size = 32;
+ char *addr;
+ char dst;
+ int ret;
+
+ setup_test_cache(test, size, 0, NULL);
+ addr = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY);
+ test_free(addr);
+ /* Use after free with *_nofault() */
+ ret = copy_from_kernel_nofault(&dst, addr, 1);
+ KUNIT_EXPECT_EQ(test, ret, -EFAULT);
+ KUNIT_EXPECT_FALSE(test, report_available());
+}
+
static void test_double_free(struct kunit *test)
{
const size_t size = 32;
@@ -780,6 +796,7 @@ static struct kunit_case kfence_test_cases[] = {
KFENCE_KUNIT_CASE(test_out_of_bounds_read),
KFENCE_KUNIT_CASE(test_out_of_bounds_write),
KFENCE_KUNIT_CASE(test_use_after_free_read),
+ KFENCE_KUNIT_CASE(test_use_after_free_read_nofault),
KFENCE_KUNIT_CASE(test_double_free),
KFENCE_KUNIT_CASE(test_invalid_addr_free),
KFENCE_KUNIT_CASE(test_corruption),
--
2.46.0
