On Wed, Mar 01, 2023 at 11:34:03AM -0800, Suren Baghdasaryan wrote: > Current 500ms min window size for psi triggers limits polling interval > to 50ms to prevent polling threads from using too much cpu bandwidth by > polling too frequently. However the number of cgroups with triggers is > unlimited, so this protection can be defeated by creating multiple > cgroups with psi triggers (triggers in each cgroup are served by a single > "psimon" kernel thread). > Instead of limiting min polling period, which also limits the latency of > psi events, it's better to limit psi trigger creation to authorized users > only, like we do for system-wide psi triggers (/proc/pressure/* files can > be written only by processes with CAP_SYS_RESOURCE capability). This also > makes access rules for cgroup psi files consistent with system-wide ones. > Add a CAP_SYS_RESOURCE capability check for cgroup psi file writers and > remove the psi window min size limitation. > > Suggested-by: Sudarshan Rajagopalan <quic_sudaraja@xxxxxxxxxxx> > Link: https://lore.kernel.org/all/cover.1676067791.git.quic_sudaraja@xxxxxxxxxxx/ > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > --- > kernel/cgroup/cgroup.c | 10 ++++++++++ > kernel/sched/psi.c | 4 +--- > 2 files changed, 11 insertions(+), 3 deletions(-) > > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > index 935e8121b21e..b600a6baaeca 100644 > --- a/kernel/cgroup/cgroup.c > +++ b/kernel/cgroup/cgroup.c > @@ -3867,6 +3867,12 @@ static __poll_t cgroup_pressure_poll(struct kernfs_open_file *of, > return psi_trigger_poll(&ctx->psi.trigger, of->file, pt); > } > > +static int cgroup_pressure_open(struct kernfs_open_file *of) > +{ > + return (of->file->f_mode & FMODE_WRITE && !capable(CAP_SYS_RESOURCE)) ? > + -EPERM : 0; > +} I agree with the change, but it's a bit unfortunate that this check is duplicated between system and cgroup. What do you think about psi_trigger_create() taking the file and checking FMODE_WRITE and CAP_SYS_RESOURCE against file->f_cred?
