tracing/user_events: Ensure bit is cleared on unregister

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.

Link: https://lkml.kernel.org/r/20230425225107.8525-3-beaub@linux.microsoft.com
Suggested-by: Doug Cook <dcook@linux.microsoft.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 546d47a..4f9ae63 100644 (file)
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -2149,6 +2149,35 @@ 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.
  */
@@ -2193,6 +2222,11 @@ 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 e0323d3..5125c42 100644 (file)
--- 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) {