From 2407794f2298ee83b38be3aae71867d6d90e87ae Mon Sep 17 00:00:00 2001 From: Odin Ugedal Date: Sat, 16 Jan 2021 18:36:33 +0100 Subject: [PATCH] cgroup: fix psi monitor for root cgroup commit 385aac1519417b89cb91b77c22e4ca21db563cd0 upstream. Fix NULL pointer dereference when adding new psi monitor to the root cgroup. PSI files for root cgroup was introduced in df5ba5be742 by using system wide psi struct when reading, but file write/monitor was not properly fixed. Since the PSI config for the root cgroup isn't initialized, the current implementation tries to lock a NULL ptr, resulting in a crash. Can be triggered by running this as root: $ tee /sys/fs/cgroup/cpu.pressure <<< "some 10000 1000000" Signed-off-by: Odin Ugedal Reviewed-by: Suren Baghdasaryan Acked-by: Dan Schatzberg Fixes: df5ba5be7425 ("kernel/sched/psi.c: expose pressure metrics on root cgroup") Acked-by: Johannes Weiner Cc: stable@vger.kernel.org # 5.2+ Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- kernel/cgroup/cgroup.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 35faf082a709..37db8eba149a 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3627,6 +3627,7 @@ static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf, { struct psi_trigger *new; struct cgroup *cgrp; + struct psi_group *psi; cgrp = cgroup_kn_lock_live(of->kn, false); if (!cgrp) @@ -3635,7 +3636,8 @@ static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf, cgroup_get(cgrp); cgroup_kn_unlock(of->kn); - new = psi_trigger_create(&cgrp->psi, buf, nbytes, res); + psi = cgroup_ino(cgrp) == 1 ? &psi_system : &cgrp->psi; + new = psi_trigger_create(psi, buf, nbytes, res); if (IS_ERR(new)) { cgroup_put(cgrp); return PTR_ERR(new);