linux-kernel - Re: [PATCH v2 1/5] fcntl: Cast commands with int args explicitly

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Message-ID: <20230414154631.GK3390869@ZenIV>
Date:   Fri, 14 Apr 2023 16:46:31 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Luca Vizzarro <Luca.Vizzarro@....com>
Cc:     linux-kernel@...r.kernel.org,
        Christian Brauner <brauner@...nel.org>,
        Jeff Layton <jlayton@...nel.org>,
        Chuck Lever <chuck.lever@...cle.com>,
        Kevin Brodsky <Kevin.Brodsky@....com>,
        Vincenzo Frascino <Vincenzo.Frascino@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        Theodore Ts'o <tytso@....edu>,
        David Laight <David.Laight@...lab.com>,
        Mark Rutland <Mark.Rutland@....com>,
        linux-fsdevel@...r.kernel.org, linux-morello@...lists.linaro.org
Subject: Re: [PATCH v2 1/5] fcntl: Cast commands with int args explicitly

On Fri, Apr 14, 2023 at 04:24:55PM +0100, Luca Vizzarro wrote:
>  	void __user *argp = (void __user *)arg;
> +	int argi = (int)arg;

Strictly speaking, conversion from unsigned long to int is
an undefined behaviour, unless the value fits into the
range representable by int ;-)

>  	case F_SETFD:
>  		err = 0;
> -		set_close_on_exec(fd, arg & FD_CLOEXEC);
> +		set_close_on_exec(fd, argi & FD_CLOEXEC);

Why?

>  	case F_SETSIG:
>  		/* arg == 0 restores default behaviour. */
> -		if (!valid_signal(arg)) {
> +		if (!valid_signal(argi)) {

Why???

>  			break;
>  		}
>  		err = 0;
> -		filp->f_owner.signum = arg;
> +		filp->f_owner.signum = argi;
>  		break;

These two are clearly bogus and I'd like to see more details
on the series rationale, please.