RE: linux interprets an fcntl int arg as long

David Laight
2022-11-01T13:29:52Z

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@arm.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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