Re: [PATCH v3 1/4] mm/mlock: return EINVAL if len overflows for mlock/munlock

[David Hildenbrand]

On 07.02.23 02:24, mawupeng wrote:
> On 2023/2/7 1:05, David Hildenbrand wrote:
> > On 06.02.23 01:48, mawupeng wrote:
> > > On 2023/2/4 1:14, David Hildenbrand wrote:
> > > > On 28.01.23 07:32, Wupeng Ma wrote:
> > > > > From: Ma Wupeng <mawupeng1@xxxxxxxxxx>
> > > > >
> > > > > While testing mlock, we have a problem if the len of mlock is ULONG_MAX.
> > > > > The return value of mlock is zero. But nothing will be locked since the
> > > > > len in do_mlock overflows to zero due to the following code in mlock:
> > > > >
> > > > >      len = PAGE_ALIGN(len + (offset_in_page(start)));
> > > > >
> > > > > The same problem happens in munlock.
> > > > >
> > > > > Add new check and return -EINVAL to fix this overflowing scenarios since
> > > > > they are absolutely wrong.
> > > > >
> > > > > Return 0 early to avoid burn a bunch of cpu cycles if len == 0.
> > > > >
> > > > > Signed-off-by: Ma Wupeng <mawupeng1@xxxxxxxxxx>
> > > > > ---
> > > > >     mm/mlock.c | 14 ++++++++++++--
> > > > >     1 file changed, 12 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/mm/mlock.c b/mm/mlock.c
> > > > > index 7032f6dd0ce1..eb09968ba27f 100644
> > > > > --- a/mm/mlock.c
> > > > > +++ b/mm/mlock.c
> > > > > @@ -478,8 +478,6 @@ static int apply_vma_lock_flags(unsigned long start, size_t len,
> > > > >         end = start + len;
> > > > >         if (end < start)
> > > > >             return -EINVAL;
> > > > > -    if (end == start)
> > > > > -        return 0;
> > > > >         vma = mas_walk(&mas);
> > > > >         if (!vma)
> > > > >             return -ENOMEM;
> > > > > @@ -575,7 +573,13 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
> > > > >         if (!can_do_mlock())
> > > > >             return -EPERM;
> > > > >     +    if (!len)
> > > > > +        return 0;
> > > > > +
> > > > >         len = PAGE_ALIGN(len + (offset_in_page(start)));
> > > > > +    if (!len)
> > > > > +        return -EINVAL;
> > > > > +
> > > > >         start &= PAGE_MASK;
> > > >
> > > > The "ordinary" overflows are detected in apply_vma_lock_flags(), correct?
> > >
> > > Overflow is not checked anywhere however the ordinary return early if len == 0 is detected in apply_vma_lock_flags().
> >
> > I meant the
> >
> > end = start + len;
> > if (end < start)
> >      return -EINVAL;
> >
> > Essentially, what I wanted to double-check is that with your changes, we catch all kinds of overflows as documented in the man page, correct?
>
> Oh i see. You are right, The "ordinary" overflows are detected for mlock/munlock in apply_vma_lock_flags().
>
> Yes, we may need to update the man page for all these four syscalls.

E.g., mlock() already documents "EINVAL (mlock(),  mlock2(),  and 
munlock()) The result of the addition addr+len was less than addr (e.g., 
the addition may have resulted in an overflow)."

Just to rephrase my question what I wanted to double-check: are we now 
identifying all such overflows or are you aware of other corner cases?

--
Thanks,

David / dhildenb