From b8a2e3f93d412114a1539ea97b59b3e6ed6e1f9a Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 14 Mar 2023 11:59:49 -1000 Subject: [PATCH] cgroup: Make current_cgns_cgroup_dfl() safe to call after exit_task_namespace() The commit 332ea1f697be ("bpf: Add bpf_cgroup_from_id() kfunc") added bpf_cgroup_from_id() which calls current_cgns_cgroup_dfl() through cgroup_get_from_id(). However, BPF programs may be attached to a point where current->nsproxy has already been cleared to NULL by exit_task_namespace() and calling bpf_cgroup_from_id() would cause an oops. Just return the system-wide root if nsproxy has been cleared. This allows all cgroups to be looked up after the task passed through exit_task_namespace(), which semantically makes sense. Given that the only way to get this behavior is through BPF programs, it seems safe but let's see what others think. Fixes: 332ea1f697be ("bpf: Add bpf_cgroup_from_id() kfunc") Signed-off-by: Tejun Heo Link: https://lore.kernel.org/r/ZBDuVWiFj2jiz3i8@slm.duckdns.org Signed-off-by: Alexei Starovoitov --- kernel/cgroup/cgroup.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 935e812..8a5294f 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1465,8 +1465,18 @@ static struct cgroup *current_cgns_cgroup_dfl(void) { struct css_set *cset; - cset = current->nsproxy->cgroup_ns->root_cset; - return __cset_cgroup_from_root(cset, &cgrp_dfl_root); + if (current->nsproxy) { + cset = current->nsproxy->cgroup_ns->root_cset; + return __cset_cgroup_from_root(cset, &cgrp_dfl_root); + } else { + /* + * NOTE: This function may be called from bpf_cgroup_from_id() + * on a task which has already passed exit_task_namespaces() and + * nsproxy == NULL. Fall back to cgrp_dfl_root which will make all + * cgroups visible for lookups. + */ + return &cgrp_dfl_root.cgrp; + } } /* look up cgroup associated with given css_set on the specified hierarchy */ -- 2.7.4