netdev - Re: [PATCH v5 0/9] Improve the copy of task comm

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Message-ID: <CAHk-=whWtUC-AjmGJveAETKOMeMFSTwKwu99v7+b6AyHMmaDFA@mail.gmail.com>
Date: Mon, 5 Aug 2024 14:28:21 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Yafang Shao <laoar.shao@...il.com>
Cc: akpm@...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
Subject: Re: [PATCH v5 0/9] Improve the copy of task comm

On Sun, 4 Aug 2024 at 00:56, Yafang Shao <laoar.shao@...il.com> wrote:
>
> There is a BUILD_BUG_ON() inside get_task_comm(), so when you use
> get_task_comm(), it implies that the BUILD_BUG_ON() is necessary.

Let's just remove that silly BUILD_BUG_ON(). I don't think it adds any
value, and honestly, it really only makes this patch-series uglier
when reasonable uses suddenly pointlessly need that double-underscore
version..

So let's aim at

 (a) documenting that the last byte in 'tsk->comm{}' is always
guaranteed to be NUL, so that the thing can always just be treated as
a string. Yes, it may change under us, but as long as we know there is
always a stable NUL there *somewhere*, we really really don't care.

 (b) removing __get_task_comm() entirely, and replacing it with a
plain 'str*cpy*()' functions

The whole (a) thing is a requirement anyway, since the *bulk* of
tsk->comm really just seems to be various '%s' things in printk
strings etc.

And once we just admit that we can use the string functions, all the
get_task_comm() stuff is just unnecessary.

And yes, some people may want to use the strscpy_pad() function
because they want to fill the whole destination buffer. But that's
entirely about the *destination* use, not the tsk->comm[] source, so
it has nothing to do with any kind of "get_task_comm()" logic, and it
was always wrong to care about the buffer sizes magically matching.

Hmm?

                Linus