On Wed, Apr 27, 2011 at 05:57, Andrea Righi wrote: > On Wed, Apr 27, 2011 at 05:50:04AM -0400, Mike Frysinger wrote: >> On Wed, Apr 27, 2011 at 05:47, Andrea Righi wrote: >> > On Wed, Apr 27, 2011 at 05:10:41AM -0400, Mike Frysinger wrote: >> >> On Wed, Apr 27, 2011 at 05:01, Andrea Righi wrote: >> >> > On Wed, Apr 27, 2011 at 10:14:53AM +1000, Dave Chinner wrote: >> >> >> On Tue, Apr 26, 2011 at 11:35:27PM +0200, Andrea Righi wrote: >> >> >> > This functionality can be used by all the applications that want to have a >> >> >> > better control over the page cache management (for example to immediately drop >> >> >> > pages that for sure will not be reused in the near future, without calling >> >> >> > posix_fadvise() for all the files they've touched), or to provide a more fine >> >> >> > grained debugging feature usable by the filesystem benchmarks. >> >> >> > >> >> >> > The system call does not require root privileges and it can be called by any >> >> >> > unprivileged application. For example, we can write a userspace tool to run >> >> >> > something like this: >> >> >> > >> >> >> > Â $ drop-pagecache /path/file_or_dir >> >> >> >> >> >> That's a potential DOS vector, I think. Drop the pagecache in a hard >> >> >> loop on the root fs of a busy server and watch it crawl... >> >> > >> >> > Yes, probably we could allow only the CAP_SYS_ADMIN tasks to execute >> >> > this syscall. >> >> >> >> if /proc/sys/vm/drop_caches has any checks other than file permission >> >> checks (i.e. UID==0), it'd probably be better to copy those rather >> >> than picking something different. >> > >> > ok, what about checking current_euid() == 0? >> >> that's not what i meant. Âif the drop_caches file already has certain >> cap checks/whatever in place, let's use those. Âif it doesnt, then >> picking a cap level as you proposed makes sense. > > mmh, drop_caches has a file ownership (root:root) and a permission mask > (0644), how to apply the same checks to a system call? The most similar > thing seems to check the current euid. Am I missing something? my (limited) understanding is that you should be using cap checks, not UID -mike -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
