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

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Message-Id: <20230425234322.64936672edb26dd2afdb3a55@kernel.org>
Date:   Tue, 25 Apr 2023 23:43:22 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        dcook@...ux.microsoft.com, alanau@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] tracing/user_events: Ensure write index cannot be
 negative

On Tue, 11 Apr 2023 14:17:07 -0700
Beau Belgrave <beaub@...ux.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@...ux.microsoft.com>
> Signed-off-by: Beau Belgrave <beaub@...ux.microsoft.com>

Looks good to me.

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