Re: [PATCH 1/3] tracing/user_events: Ensure write index cannot be negative

Masami Hiramatsu
2023-04-25T14:43:31Z

On Tue, 11 Apr 2023 14:17:07 -0700
Beau Belgrave <beaub@linux.microsoft.com> wrote:

> The write index indicates which event the data is for and accesses a
> per-file array. The index is passed by user processes during write()
> calls as the first 4 bytes. Ensure that it cannot be negative by
> returning -EINVAL to prevent out of bounds accesses.
>
> Update ftrace self-test to ensure this occurs properly.
>
> Fixes: 7f5a08c79df3 ("user_events: Add minimal support for trace_event into ftrace")
> Reported-by: Doug Cook <dcook@linux.microsoft.com>
> Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks!

> ---
> kernel/trace/trace_events_user.c | 3 +++
> tools/testing/selftests/user_events/ftrace_test.c | 5 +++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index cc8c6d8b69b5..e7dff24aa724 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -1821,6 +1821,9 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
> if (unlikely(copy_from_iter(&idx, sizeof(idx), i) != sizeof(idx)))
> return -EFAULT;
>
> + if (idx < 0)
> + return -EINVAL;
> +
> rcu_read_lock_sched();
>
> refs = rcu_dereference_sched(info->refs);
> diff --git a/tools/testing/selftests/user_events/ftrace_test.c b/tools/testing/selftests/user_events/ftrace_test.c
> index aceafacfb126..91272f9d6fce 100644
> --- a/tools/testing/selftests/user_events/ftrace_test.c
> +++ b/tools/testing/selftests/user_events/ftrace_test.c
> @@ -296,6 +296,11 @@ TEST_F(user, write_events) {
> ASSERT_NE(-1, writev(self->data_fd, (const struct iovec *)io, 3));
> after = trace_bytes();
> ASSERT_GT(after, before);
> +
> + /* Negative index should fail with EINVAL */
> + reg.write_index = -1;
> + ASSERT_EQ(-1, writev(self->data_fd, (const struct iovec *)io, 3));
> + ASSERT_EQ(EINVAL, errno);
> }
>
> TEST_F(user, write_fault) {
> --
> 2.25.1
>

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>