On 07/12, Kees Cook wrote: > > On Tue, Jul 12, 2016 at 9:39 AM, Oleg Nesterov <oleg@xxxxxxxxxx> 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>