On Fri, Dec 6, 2024 at 10:35 AM Marco Vanotti <mvanotti@xxxxxxxxxx> wrote:
>
> On Fri, Dec 6, 2024 at 12:20 PM Brian Geffon <bgeffon@xxxxxxxxxx> wrote:
> >
> > Two non-mutually exclusive paths can land in mremap_to, MREMAP_FIXED
> > and MREMAP_DONTUNMAP which are called from mremap(). In the case of
> > MREMAP_FIXED we must validate the new_addr to ensure that the new
> > address is valid. In the case of MREMAP_DONTUNMAP without MREMAP_FIXED
> > a new address is specified as a hint, just like it would be in the
> > case of mmap. In this second case we don't need to perform any checks
> > because get_unmapped_area() will align new_addr, just like it would in
> > the case of mmap.
> >
> > Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx>
> > Reported-by: Marco Vanotti <mvanotti@xxxxxxxxxx>
> > ---
> > mm/mremap.c | 26 +++++++++++++++++++-------
> > 1 file changed, 19 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/mremap.c b/mm/mremap.c
> > index 60473413836b..286ffdb883df 100644
> > --- a/mm/mremap.c
> > +++ b/mm/mremap.c
> > @@ -912,15 +912,27 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> > unsigned long ret;
> > unsigned long map_flags = 0;
> >
> > - if (offset_in_page(new_addr))
> > - return -EINVAL;
> > + /*
> > + * Two non-mutually exclusive paths can land in mremap_to, MREMAP_FIXED
> > + * and MREMAP_DONTUNMAP which are called from mremap(). In the case of
> > + * MREMAP_FIXED we must validate the new_addr to ensure that the new
> > + * address is valid. In the case of MREMAP_DONTUNMAP without MREMAP_FIXED
> > + * a new address is specified as a hint, just like it would be in the
> > + * case of mmap. In this second case we don't need to perform any checks
> > + * because get_unmapped_area() will align new_addr, just like it would in
> > + * the case of mmap.
> > + */
> A few lines below we also check for MREMAP_FIXED before calling
> do_unmap, can't we do the validation there?
I don't have a strong preference either way. I can mail a v2 with this
suggestion.
> > + if (flags & MREMAP_FIXED) {
> > + if (offset_in_page(new_addr))
> > + return -EINVAL;
> >
> > - if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
> > - return -EINVAL;
> > + if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
> > + return -EINVAL;
> >
> > - /* Ensure the old/new locations do not overlap */
> > - if (addr + old_len > new_addr && new_addr + new_len > addr)
> > - return -EINVAL;
> > + /* Ensure the old/new locations do not overlap */
> > + if (addr + old_len > new_addr && new_addr + new_len > addr)
> > + return -EINVAL;
> > + }
> >
> > /*
> > * move_vma() need us to stay 4 maps below the threshold, otherwise
> > --
> > 2.47.0.338.g60cca15819-goog
> >
