On Wed, Apr 6, 2011 at 5:59 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Apr 6, 2011 at 8:43 AM, Hugh Dickins <hughd@xxxxxxxxxx> wrote: >> >> I was about to send you my own UNTESTED patch: let me append it anyway, >> I think it is more correct than yours (it's the offset of vm_end we need >> to worry about, and there's the funny old_len,new_len stuff). > > Umm. That's what my patch did too. The > > Â pgoff = (addr - vma->vm_start) >> PAGE_SHIFT; > > is the "offset of the pgoff" from the original mapping, then we do > > Â pgoff += vma->vm_pgoff; > > to get the pgoff of the new mapping, and then we do > > Â if (pgoff + (new_len >> PAGE_SHIFT) < pgoff) > > to check that the new mapping is ok. > > I think yours is equivalent, just a different (and odd - that > linear_page_index() thing will do lots of unnecessary shifts and > hugepage crap) way of writing it. > >>ÂSee what you think - sorry, I'm going out now. > > I think _yours_ is conceptually buggy, because I think that test for > "vma->vm_file" is wrong. > > Yes, new anonymous mappings set vm_pgoff to the virtual address, but > that's not true for mremap() moving them around, afaik. > > Admittedly it's really hard to get to the overflow case, because the > address is shifted down, so even if you start out with an anonymous > mmap at a high address (to get a big vm_off), and then move it down > and expand it (to get a big size), I doubt you can possibly overflow. > But I still don't think that the test for vm_file is semantically > sensible, even if it might not _matter_. > > But whatever. I suspect both our patches are practically doing the > same thing, and it would be interesting to hear if it actually fixes > the issue. Maybe there is some other way to mess up vm_pgoff that I > can't think of right now. Testing with Linus' patch. Will let you know in a few hours. -- Robert ÅwiÄcki -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href