BPF_PROG_QUERY gets the cgroup from an fd before it takes cgroup_mutex. If the cgroup is removed in between and its bpf refcount drops to zero, cgroup_bpf_release() can run first. It frees the effective arrays but leaves the pointers, so a BPF_F_QUERY_EFFECTIVE query then reads freed memory. The window is small because the release work also takes cgroup_mutex. Check under the lock that the bpf refcount isn't zero, and return -ENOENT if it is, the error the fd lookup gives for a removed cgroup. The release work only runs after the count hits zero, and it takes the same lock. Reproduced in a VM with a debug-only delay between the fd lookup and the lock: KASAN reports a use-after-free in cgroup_bpf_prog_query(). With this patch, the query returns -ENOENT. Fixes: 4bfc0bb2c60e ("bpf: decouple the lifetime of cgroup_bpf from cgroup itself") Signed-off-by: Shakeel Butt --- kernel/bpf/cgroup.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index 57a785241d42..9258c2669fa8 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -1446,6 +1446,14 @@ static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr, if (effective_query && prog_attach_flags) return -EINVAL; + /* + * cgroup_bpf_release() frees the effective arrays once the bpf + * refcount is zero. It takes this lock too, so a nonzero count means + * the arrays are still valid. + */ + if (percpu_ref_is_zero(&cgrp->bpf.refcnt)) + return -ENOENT; + if (type == BPF_STRUCT_OPS) { u32 type_id = attr->query.type_id; -- 2.53.0-Meta