On Thu, 19 Nov 2009 10:57:08 -0800 ebiederm@xxxxxxxxxxxx (Eric W. Biederman) wrote: > Jeff Layton <jlayton@xxxxxxxxxx> writes: > > > On Thu, 19 Nov 2009 09:07:16 -0800 > > ebiederm@xxxxxxxxxxxx (Eric W. Biederman) wrote: > > > >> > >> Nacked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > >> > >> This is broken. If the referenced file is in a different mount namespace > >> the path returned could point to a completely different path in your > >> own mount namespace. Even in your own mount namespace this makes the > >> proc symlinks racy and not guaranteed to return the file of interest. > >> > >> I don't see any hope of this approach ever working. > >> > >> Eric > >> > > > > Then is proc_pid_readlink broken in the same way? > > proc_pid_readlink has the same deficiencies. The race is fundamental > to all readlink operations, the difference is that for normal symlinks > it is a don't care, and for proc it is incorrect behavior if you follow > the symlink to the wrong file. If you are dealing with a file in a > different namespace or a socket what you get back doesn't actually > work as a file in your local namespace but that is the best we can do > with a pathname, and if you know the context of what is going on readlink > is still useful. > > Adding all of the short comings to followlink that readlink has is a problem, > especially as followlink does much better now. > > At a practical level I think your changes are much easier to exploit than > Pavels contrived example. > > I really don't have any problems with your first patch to proc to add the > missing revalidate. > Thanks, that makes sense. The raciness was evident once you pointed it out, so I think you're correct that we can't take this approach. Adding the missing revalidations is fine, but I don't believe that helps to fix Pavel's issue. I'll go back and take a more careful look at the suggestion that Miklos made and see whether it makes sense to implement a new FS_* flag for this, and see what it'll take to fix Pavel's issue. -- Jeff Layton <jlayton@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
