On Mon, Dec 14, 2015 at 06:11:16PM +0300, Cyrill Gorcunov wrote: > On Mon, Dec 14, 2015 at 03:51:26PM +0100, Quentin Casasnovas wrote: > ... > > > > Do we want to fold may_expand_anon_vm() into may_expand_vm() (potentially > > passing it the flags/struct file if needed) so there is just one such > > helper function? Rationale being that it then gets hard to see what > > restricts what, and it's easy to miss one place. > > I tried to make the patch small as possible (because otherwise indeed > I would have to pass @vm_file|@file as additional argument). This won't > be a problem but may_expand_vm is called way more times than > may_expand_anon_vm. That's the only rationale I followed. > > > For example, I couldn't find anything preventing a user to > > mmap(MAP_GROWSDOWN) and uses that as a base to get pages that would not be > > accounted for in your patch (making it a poor-man mremap()). > > growsup/down stand for stack usage iirc, so it was intentionally > not accounted here. > Right, but in the same vein of Linus saying RLIMIT_DATA is/was useless because everyone could use mmap() instead of brk() to get anonymous memory, what's the point of restricting "almost-all" anonymous memory if one can just use MAP_GROWSDOWN/UP and cause repeated page faults to extend that mapping, circumventing your checks? That makes the new restriction as useless as what RLIMIT_DATA used to be, doesn't it? > > > > I only had a quick look so apologies if this is handled and I missed it :) > > thanks for feedback! also take a look on Kostya's patch, I think it's > even better approach (and I like it more than mine). Ha I'm not subscribed to LKML so I missed those, I suppose you can ignore my comments then! :) Quentin -- 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>