On Wed, Aug 09, 2023 at 07:25:19PM -0300, André Almeida wrote:
> Hi Peter,
>
> Em 07/08/2023 09:18, Peter Zijlstra escreveu:
> > To complement sys_futex_waitv() add sys_futex_wake(). This syscall
> > implements what was previously known as FUTEX_WAKE_BITSET except it
> > uses 'unsigned long' for the bitmask and takes FUTEX2 flags.
> >
> > The 'unsigned long' allows FUTEX2_SIZE_U64 on 64bit platforms.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > Acked-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > ---
>
> [...]
>
> > +/*
> > + * sys_futex_wake - Wake a number of futexes
> > + * @uaddr: Address of the futex(es) to wake
> > + * @mask: bitmask
> > + * @nr: Number of the futexes to wake
> > + * @flags: FUTEX2 flags
> > + *
> > + * Identical to the traditional FUTEX_WAKE_BITSET op, except it is part of the
> > + * futex2 family of calls.
> > + */
> > +
> > +SYSCALL_DEFINE4(futex_wake,
> > + void __user *, uaddr,
> > + unsigned long, mask,
> > + int, nr,
> > + unsigned int, flags)
> > +{
>
> Do you think we could have a
>
> if (!nr)
> return 0;
>
> here? Otherwise, calling futex_wake(&f, 0, flags) will wake 1 futex (if
> available), which is a strange undocumented behavior in my opinion.
Oh 'cute' that.. yeah, but how about I put it ...
> > + if (flags & ~FUTEX2_VALID_MASK)
> > + return -EINVAL;
> > +
> > + flags = futex2_to_flags(flags);
> > + if (!futex_flags_valid(flags))
> > + return -EINVAL;
> > +
> > + if (!futex_validate_input(flags, mask))
> > + return -EINVAL;
here, because otherwise we get:
sys_futex_wake(&f, 0xFFFF, 0, FUTEX2_SIZE_U8)
to return 0, even though that is 'obviously' nonsensical and should
return -EINVAL. Or even garbage flags would be 'accepted'.
(because 0xFFFF is larger than U8 can accomodate)
> > +
> > + return futex_wake(uaddr, flags, nr, mask);
> > +}
