netdev - Re: [PATCH v6 7/9] tracing: Replace strncpy() with strscpy()

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Message-ID: <hbjxkyhugi27mbrj5zo2thfdg2gotz6syz6qoeows6l6qwbzkt@c3yb26z4pn62>
Date: Tue, 13 Aug 2024 15:19:25 -0700
From: Justin Stitt <justinstitt@...gle.com>
To: Yafang Shao <laoar.shao@...il.com>
Cc: akpm@...ux-foundation.org, torvalds@...ux-foundation.org, 
	ebiederm@...ssion.com, alexei.starovoitov@...il.com, rostedt@...dmis.org, 
	catalin.marinas@....com, penguin-kernel@...ove.sakura.ne.jp, linux-mm@...ck.org, 
	linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, audit@...r.kernel.org, 
	linux-security-module@...r.kernel.org, selinux@...r.kernel.org, bpf@...r.kernel.org, 
	netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH v6 7/9] tracing: Replace strncpy() with strscpy()

Hi,

On Mon, Aug 12, 2024 at 10:29:31AM GMT, Yafang Shao wrote:
> Using strscpy() to read the task comm ensures that the name is
> always NUL-terminated, regardless of the source string. This approach also
> facilitates future extensions to the task comm.

Thanks for sending patches replacing str{n}cpy's!

I believe there's at least two more instances of strncpy in trace.c as
well as in trace_events_hist.c (for a grand total of 6 instances in the
files you've touched in this specific patch).

It'd be great if you could replace those instances in this patch as well :>)

This would help greatly with [1].

> 
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> ---
>  kernel/trace/trace.c             | 2 +-
>  kernel/trace/trace_events_hist.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 578a49ff5c32..1b2577f9d734 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1907,7 +1907,7 @@ __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
>  	max_data->critical_start = data->critical_start;
>  	max_data->critical_end = data->critical_end;
>  
> -	strncpy(max_data->comm, tsk->comm, TASK_COMM_LEN);
> +	strscpy(max_data->comm, tsk->comm, TASK_COMM_LEN);

If max_data->comm wants to be NUL-terminated then this is the right
replacement. Without knowing how the trace stack works at all, it's hard
for me to tell if that is the case.

There's a length-supplied format specifier for which this comm field is
used with; Either this is just another safeguard against spilling over
the buffer or this field really doesn't care about NUL-termination.
| seq_printf(m, "#    | task: %.16s-%d "
|       "(uid:%d nice:%ld policy:%ld rt_prio:%ld)\n",
|       data->comm, data->pid,

In the event this field doesn't need to be NUL-terminated then we are
introducing an off-by-one error where we are copying one less useful
byte with strscpy -- Linus pointed out earlier [2] that these things all
just want to be c-strings so this is probably the right change :>)

>  	max_data->pid = tsk->pid;
>  	/*
>  	 * If tsk == current, then use current_uid(), as that does not use
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 6ece1308d36a..4cd24c25ce05 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1599,7 +1599,7 @@ static inline void save_comm(char *comm, struct task_struct *task)
>  		return;
>  	}
>  
> -	strncpy(comm, task->comm, TASK_COMM_LEN);
> +	strscpy(comm, task->comm, TASK_COMM_LEN);
>  }
>  
>  static void hist_elt_data_free(struct hist_elt_data *elt_data)
> -- 
> 2.43.5
> 

Link: https://github.com/KSPP/linux/issues/90 [1]
Link: https://lore.kernel.org/all/CAHk-=whWtUC-AjmGJveAETKOMeMFSTwKwu99v7+b6AyHMmaDFA@mail.gmail.com/ [2]

Thanks
Justin