[PATCH 2/3] tracing/user_events: Ensure bit is cleared on unregister

Beau Belgrave
2023-04-11T21:17:18Z

If an event is enabled and a user process unregisters user_events, the
bit is left set. Fix this by always clearing the bit in the user process
if unregister is successful.

Update abi self-test to ensure this occurs properly.

Suggested-by: Doug Cook <dcook@linux.microsoft.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
---
kernel/trace/trace_events_user.c | 34 +++++++++++++++++++
.../testing/selftests/user_events/abi_test.c | 9 +++--
2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index e7dff24aa724..eb195d697177 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -2146,6 +2146,35 @@ static long user_unreg_get(struct user_unreg __user *ureg,
return ret;
}

+static int user_event_mm_clear_bit(struct user_event_mm *user_mm,
+ unsigned long uaddr, unsigned char bit)
+{
+ struct user_event_enabler enabler;
+ int result;
+
+ memset(&enabler, 0, sizeof(enabler));
+ enabler.addr = uaddr;
+ enabler.values = bit;
+retry:
+ /* Prevents state changes from racing with new enablers */
+ mutex_lock(&event_mutex);
+
+ /* Force the bit to be cleared, since no event is attached */
+ mmap_read_lock(user_mm->mm);
+ result = user_event_enabler_write(user_mm, &enabler, false);
+ mmap_read_unlock(user_mm->mm);
+
+ mutex_unlock(&event_mutex);
+
+ if (result) {
+ /* Attempt to fault-in and retry if it worked */
+ if (!user_event_mm_fault_in(user_mm, uaddr))
+ goto retry;
+ }
+
+ return result;
+}
+
/*
* Unregisters an enablement address/bit within a task/user mm.
*/
@@ -2190,6 +2219,11 @@ static long user_events_ioctl_unreg(unsigned long uarg)

mutex_unlock(&event_mutex);

+ /* Ensure bit is now cleared for user, regardless of event status */
+ if (!ret)
+ ret = user_event_mm_clear_bit(mm, reg.disable_addr,
+ reg.disable_bit);
+
return ret;
}

diff --git a/tools/testing/selftests/user_events/abi_test.c b/tools/testing/selftests/user_events/abi_test.c
index e0323d3777a7..5125c42efe65 100644
--- a/tools/testing/selftests/user_events/abi_test.c
+++ b/tools/testing/selftests/user_events/abi_test.c
@@ -109,13 +109,16 @@ TEST_F(user, enablement) {
ASSERT_EQ(0, change_event(false));
ASSERT_EQ(0, self->check);

- /* Should not change after disable */
+ /* Ensure kernel clears bit after disable */
ASSERT_EQ(0, change_event(true));
ASSERT_EQ(1, self->check);
ASSERT_EQ(0, reg_disable(&self->check, 0));
+ ASSERT_EQ(0, self->check);
+
+ /* Ensure doesn't change after unreg */
+ ASSERT_EQ(0, change_event(true));
+ ASSERT_EQ(0, self->check);
ASSERT_EQ(0, change_event(false));
- ASSERT_EQ(1, self->check);
- self->check = 0;
}

TEST_F(user, bit_sizes) {
--
2.25.1