linux-kernel - Re: [PATCH] sysctl: handle table->maxlen properly for proc

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Message-ID: <YoZBbcEHcLqsAssF@casper.infradead.org>
Date:   Thu, 19 May 2022 14:09:01 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        duanxiongchun@...edance.com, smuchun@...il.com,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>
Subject: Re: [PATCH] sysctl: handle table->maxlen properly for proc_dobool

On Thu, May 19, 2022 at 08:55:05PM +0800, Muchun Song wrote:
> @@ -428,6 +428,8 @@ static int do_proc_dobool_conv(bool *negp, unsigned long *lvalp,
>  				int write, void *data)
>  {
>  	if (write) {
> +		if (*negp || (*lvalp != 0 && *lvalp != 1))
> +			return -EINVAL;
>  		*(bool *)valp = *lvalp;
>  	} else {
>  		int val = *(bool *)valp;

Is this the right approach?  Or should we do as C does and interpret
writing non-zero as true?  ie:

		*(bool *)valp = (bool)*lvalp;

(is that cast needed?  It wouldn't be if it were an int, but bool is a
bit weird)