Messages in this thread | | | Date | Wed, 13 Jul 2016 19:00:49 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/2] mm: refuse wrapped vm_brk requests |
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On 07/12, Kees Cook wrote: > > On Tue, Jul 12, 2016 at 9:39 AM, Oleg Nesterov <oleg@redhat.com> wrote: > > > > I tried to say that, with or without this change, sys_brk() should check > > for overflow too, otherwise it looks buggy. > > Hmm, it's not clear to me the right way to fix sys_brk(), but it looks > like my change to do_brk() would catch the problem?
How?
Once again, afaics nothing bad can happen, sys_brk() will silently fail, just the code looks wrong anyway.
Suppose that newbrk == 0 due to overflow, then both
if (find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE)) goto out;
and if (do_brk(oldbrk, newbrk-oldbrk) < 0) goto out;
look buggy.
find_vma_intersection(start_addr, end_addr) expects that start_addr < end_addr. Again, we do not really care if it returns NULL or not, and newbrk == 0 just means it will certainly return NULL if there is something above oldbrk. Just looks buggy/confusing.
do_brk(0 - oldbrk) will fail and this is what we want. But not because your change will catch the problem, PAGE_ALIGNE(-oldbrk) won't necessarily overflow. However, -oldbrk > TASK_SIZE so get_unmapped_area() should fail.
Nevermind, this is almost off-topic, so let me repeat just in case that both patches look good to me.
Oleg.
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