[PATCH 1/2] Input: tests - fix use-after-free and refcount underflow in input_test_exit()

[Geert Uytterhoeven]

With CONFIG_DEBUG_SLAB=y:

# Subtest: input_core
1..3
input: Test input device as /devices/virtual/input/input1
8<--- cut here ---
Unable to handle kernel paging request at virtual address 6b6b6dd7 when read
...
__lock_acquire from lock_acquire+0x26c/0x300
lock_acquire from _raw_spin_lock_irqsave+0x50/0x64
_raw_spin_lock_irqsave from devres_remove+0x20/0x7c
devres_remove from devres_destroy+0x8/0x24
devres_destroy from input_free_device+0x2c/0x60
input_free_device from kunit_try_run_case+0x70/0x94 [kunit]

Without CONFIG_DEBUG_SLAB=y:

KTAP version 1
# Subtest: input_core
1..3
input: Test input device as /devices/virtual/input/input1
------------[ cut here ]------------
WARNING: CPU: 0 PID: 694 at lib/refcount.c:28 refcount_warn_saturate+0x54/0x100
refcount_t: underflow; use-after-free.
...
Call Trace: [<0037cad4>] dump_stack+0xc/0x10
[<00377614>] __warn+0x7e/0xb4
[<0037768c>] warn_slowpath_fmt+0x42/0x62
[<001eee1c>] refcount_warn_saturate+0x54/0x100
[<000b1d34>] kfree_const+0x0/0x20
[<0036290a>] __kobject_del+0x0/0x6e
[<001eee1c>] refcount_warn_saturate+0x54/0x100
[<00362a1a>] kobject_put+0xa2/0xb6
[<11965770>] kunit_generic_run_threadfn_adapter+0x0/0x1c [kunit]

As per the comments for input_allocate_device() and
input_register_device(), input_free_device() must be called only to free
devices that have not been registered. input_unregister_device()
already calls input_put_device(), thus leading to a use-after-free.

Moreover, the kunit_suite.exit() method is called after every test case,
even on failures. As the test itself already does cleanups in its
failure paths, this may lead to a second use-after-free.

Fix the first issue by dropping the call to input_allocate_device() from
input_test_exit().
Fix the second issue by making the cleanup code conditional on a
successful test.

Fixes: fdefcbdd6f361841 ("Input: Add KUnit tests for some of the input core helper functions")
Signed-off-by: Geert Uytterhoeven <geert+...@glider.be>
---
drivers/input/tests/input_test.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/input/tests/input_test.c b/drivers/input/tests/input_test.c
index e5a6c1ad2167c103..8b8ac3412a70d3b4 100644
--- a/drivers/input/tests/input_test.c
+++ b/drivers/input/tests/input_test.c
@@ -43,8 +43,8 @@ static void input_test_exit(struct kunit *test)
{
struct input_dev *input_dev = test->priv;

- input_unregister_device(input_dev);
- input_free_device(input_dev);
+ if (input_dev)
+ input_unregister_device(input_dev);
}

static void input_test_poll(struct input_dev *input) { }
--
2.34.1