Messages in this thread | | | Date | Sun, 24 Aug 2014 19:41:57 +0200 | From | Manfred Spraul <> | Subject | Re: [PATCH 1/1] ipc/shm: fix the historical/wrong mm->start_stack check |
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On 08/23/2014 04:43 PM, Oleg Nesterov wrote: > The ->start_stack check in do_shmat() looks ugly and simply wrong. > > 1. ->start_stack is only valid right after exec(), the application > can switch to another stack and even unmap this area. > > 2. The reason for this check is not clear at all. The application > should know what it does. And why 4 pages? And why in fact it > requires 5 pages? > > 3. This wrongly assumes that the stack can only grown down. > > Personally I think we should simply kill this check, but I did not > dare to do this. So the patch only fixes the 1st problem (mostly to > avoid the usage of mm->start_stack) and ignores VM_GROWSUP. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Manfred Spraul <manfred@colorfullife.com> > [snip]
> + if (vma) { > + if (vma->vm_flags & VM_GROWSDOWN) > + end += PAGE_SIZE * 4; /* can't overflow */ Why is an overflow impossible? > + if (end > vma->vm_start) > + goto invalid; > + } > } > > addr = do_mmap_pgoff(file, addr, size, prot, flags, 0, &populate); -- Manfred
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