netdev - [PATCH bpf v2 1/2] bpf: Disallow tail call to programs that use cgroup storage

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Message-ID: <20251202171615.1027536-1-ameryhung@gmail.com>
Date: Tue,  2 Dec 2025 09:16:14 -0800
From: Amery Hung <ameryhung@...il.com>
To: bpf@...r.kernel.org
Cc: netdev@...r.kernel.org,
	alexei.starovoitov@...il.com,
	andrii@...nel.org,
	daniel@...earbox.net,
	martin.lau@...nel.org,
	eddyz87@...il.com,
	ameryhung@...il.com,
	kernel-team@...a.com
Subject: [PATCH bpf v2 1/2] bpf: Disallow tail call to programs that use cgroup storage

Mitigate a possible NULL pointer dereference in bpf_get_local_storage()
by disallowing tail call to programs that use cgroup storage. Cgroup
storage is allocated lazily when attaching a cgroup bpf program. With
tail call, it is possible for a callee BPF program to see a NULL
storage pointer if the caller prorgam does not use cgroup storage.

Reported-by: Yinhao Hu <dddddd@...t.edu.cn>
Reported-by: Kaiyan Mei <M202472210@...t.edu.cn>
Reported-by: Dongliang Mu <dzm91@...t.edu.cn>
Closes: https://lore.kernel.org/bpf/c9ac63d7-73be-49c5-a4ac-eb07f7521adb@hust.edu.cn/
Signed-off-by: Amery Hung <ameryhung@...il.com>
---
 kernel/bpf/arraymap.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 1eeb31c5b317..9c3f86ef9d16 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -884,8 +884,9 @@ int bpf_fd_array_map_update_elem(struct bpf_map *map, struct file *map_file,
 				 void *key, void *value, u64 map_flags)
 {
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
+	u32 i, index = *(u32 *)key, ufd;
 	void *new_ptr, *old_ptr;
-	u32 index = *(u32 *)key, ufd;
+	struct bpf_prog *prog;
 
 	if (map_flags != BPF_ANY)
 		return -EINVAL;
@@ -898,6 +899,14 @@ int bpf_fd_array_map_update_elem(struct bpf_map *map, struct file *map_file,
 	if (IS_ERR(new_ptr))
 		return PTR_ERR(new_ptr);
 
+	if (map->map_type == BPF_MAP_TYPE_PROG_ARRAY) {
+		prog = (struct bpf_prog *)new_ptr;
+
+		for_each_cgroup_storage_type(i)
+			if (prog->aux->cgroup_storage[i])
+				return -EINVAL;
+	}
+
 	if (map->ops->map_poke_run) {
 		mutex_lock(&array->aux->poke_mutex);
 		old_ptr = xchg(array->ptrs + index, new_ptr);
-- 
2.47.3