linux-kernel - RE: linux interprets an fcntl int arg as long

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Message-ID: <267402c9e66a4cac91a2e1df749dea6a@AcuMS.aculab.com>
Date:   Tue, 1 Nov 2022 13:29:41 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Mark Rutland' <mark.rutland@....com>
CC:     'Szabolcs Nagy' <szabolcs.nagy@....com>,
        Theodore Ts'o <tytso@....edu>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: linux interprets an fcntl int arg as long

From: Mark Rutland
> Sent: 01 November 2022 13:13
> 
> On Tue, Nov 01, 2022 at 12:19:51PM +0000, David Laight wrote:
> > From: 'Szabolcs Nagy' <szabolcs.nagy@....com>
> > > Sent: 01 November 2022 11:45
> > >
> > > The 11/01/2022 10:02, David Laight wrote:
> > > > From: Szabolcs Nagy
> 
> > > kernel code:
> > > ------------
> > > SYSCALL_DEFINE3(fcntl, unsigned int, fd, unsigned int, cmd, unsigned long, arg)
> > > {
> >
> > That is just a wrapper and calls do_fcntl().
> > which needs changing to be add:
> > 	arg &= ~0U;
> > before the switch(cmd) {
> 
> Just to check, do you mean the switch in do_fcntl(), or the switch within memfd_fcntl() ?
> 
> The former handles other APIs which do expect arg to be a long (e.g.
> F_SET_RW_HINT and F_GET_RW_HINT expect it to hold a full 64-bit pointer), so
> that'd break things.

The assignment to argv is earlier.

	David

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