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Date:   Sun, 3 Oct 2021 03:31:39 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Yafang Shao <laoar.shao@gmail.com>
Cc:     akpm@linux-foundation.org, pmladek@suse.com, peterz@infradead.org,
        valentin.schneider@arm.com, keescook@chromium.org,
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        robdclark@chromium.org, christian@brauner.io,
        dietmar.eggemann@arm.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] kernel: replace sizeof(task->comm) with TASK_COMM_LEN
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References: <20210929115036.4851-1-laoar.shao@gmail.com>
 <20210929115036.4851-2-laoar.shao@gmail.com>
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On Wed, Sep 29, 2021 at 11:50:32AM +0000, Yafang Shao wrote:

> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2265,7 +2265,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  		unsigned long, arg4, unsigned long, arg5)
>  {
>  	struct task_struct *me = current;
> -	unsigned char comm[sizeof(me->comm)];
> +	unsigned char comm[TASK_COMM_LEN];
>  	long error;
>  
>  	error = security_task_prctl(option, arg2, arg3, arg4, arg5);

Slightly below you have this:
        case PR_SET_NAME:
                comm[sizeof(me->comm) - 1] = 0;
                if (strncpy_from_user(comm, (char __user *)arg2,
                                      sizeof(me->comm) - 1) < 0)
                        return -EFAULT;
                set_task_comm(me, comm);
                proc_comm_connector(me);
                break;

How had that been tested?