On Wed, May 22, 2019 at 11:00:22PM +0300, Amir Goldstein wrote: > On Wed, May 22, 2019 at 9:57 PM Christian Brauner <christian@xxxxxxxxxx> wrote: > > > > On May 22, 2019 8:29:37 PM GMT+02:00, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > >On Wed, May 22, 2019 at 7:32 PM Christian Brauner > > ><christian@xxxxxxxxxx> wrote: > > >> > > >> This removes two redundant capable(CAP_SYS_ADMIN) checks from > > >> fanotify_init(). > > >> fanotify_init() guards the whole syscall with capable(CAP_SYS_ADMIN) > > >at the > > >> beginning. So the other two capable(CAP_SYS_ADMIN) checks are not > > >needed. > > > > > >It's intentional: > > > > > >commit e7099d8a5a34d2876908a9fab4952dabdcfc5909 > > >Author: Eric Paris <eparis@xxxxxxxxxx> > > >Date: Thu Oct 28 17:21:57 2010 -0400 > > > > > > fanotify: limit the number of marks in a single fanotify group > > > > > >There is currently no limit on the number of marks a given fanotify > > >group > > >can have. Since fanotify is gated on CAP_SYS_ADMIN this was not seen > > >as > > >a serious DoS threat. This patch implements a default of 8192, the > > >same as > > >inotify to work towards removing the CAP_SYS_ADMIN gating and > > >eliminating > > > the default DoS'able status. > > > > > > Signed-off-by: Eric Paris <eparis@xxxxxxxxxx> > > > > > >There idea is to eventually remove the gated CAP_SYS_ADMIN. > > >There is no reason that fanotify could not be used by unprivileged > > >users > > >to setup inotify style watch on an inode or directories children, see: > > >https://patchwork.kernel.org/patch/10668299/ > > > > > >> > > >> Fixes: 5dd03f55fd2 ("fanotify: allow userspace to override max queue > > >depth") > > >> Fixes: ac7e22dcfaf ("fanotify: allow userspace to override max > > >marks") > > > > > >Fixes is used to tag bug fixes for stable. > > >There is no bug. > > > > > >Thanks, > > >Amir. > > > > Interesting. When do you think the gate can be removed? > > Nobody is working on this AFAIK. > What I posted was a simple POC, but I have no use case for this. > In the patchwork link above, Jan has listed the prerequisites for > removing the gate. > > One of the prerequisites is FAN_REPORT_FID, which is now merged. > When events gets reported with fid instead of fd, unprivileged user > (hopefully) cannot use fid for privilege escalation. > > > I was looking into switching from inotify to fanotify but since it's not usable from > > non-initial userns it's a no-no > > since we support nested workloads. > > One of Jan's questions was what is the benefit of using inotify-compatible > fanotify vs. using inotify. > So what was the reason you were looking into switching from inotify to fanotify? > Is it because of mount/filesystem watch? Because making those available for Yeah. Well, I would need to look but you could probably do it safely for filesystems mountable in user namespaces (which are few). Can you do a bind-mount and then place a watch on the bind-mount or is this superblock based? Thanks! Christian
