From: Alexei Starovoitov <ast@xxxxxxxxxx>
bpf programs sometimes do:
bpf_cgrp_storage_get(&map, task->cgroups->dfl_cgrp, ...);
It is safe to do, because cgroups->dfl_cgrp pointer is set diring init and
never changes. The task->cgroups is also never NULL. It is also set during init
and will change when task switches cgroups. For any trusted task pointer
dereference of cgroups and dfl_cgrp should yield trusted pointers. The verifier
wasn't aware of this. Hence in gcc compiled kernels task->cgroups dereference
was producing PTR_TO_BTF_ID without modifiers while in clang compiled kernels
the verifier recognizes __rcu tag in cgroups field and produces
PTR_TO_BTF_ID | MEM_RCU | MAYBE_NULL.
Tag cgroups and dfl_cgrp as trusted to equalize clang and gcc behavior.
When GCC supports btf_type_tag such tagging will done directly in the type.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Acked-by: David Vernet <void@xxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
---
kernel/bpf/verifier.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index bf580f246a01..b834f3d2d81a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5046,6 +5046,11 @@ static int bpf_map_direct_read(struct bpf_map *map, int off, int size, u64 *val)
BTF_TYPE_SAFE_NESTED(struct task_struct) {
const cpumask_t *cpus_ptr;
+ struct css_set __rcu *cgroups;
+};
+
+BTF_TYPE_SAFE_NESTED(struct css_set) {
+ struct cgroup *dfl_cgrp;
};
static bool nested_ptr_is_trusted(struct bpf_verifier_env *env,
@@ -5057,6 +5062,7 @@ static bool nested_ptr_is_trusted(struct bpf_verifier_env *env,
return false;
BTF_TYPE_EMIT(BTF_TYPE_SAFE_NESTED(struct task_struct));
+ BTF_TYPE_EMIT(BTF_TYPE_SAFE_NESTED(struct css_set));
return btf_nested_type_is_trusted(&env->log, reg, off);
}
--
2.39.2
