From: Jiayuan Chen <jiayuan.chen@linux.dev>
To: Liu Jing <liujing@cmss.chinamobile.com>, ast@kernel.org
Cc: daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com,
memxor@gmail.com, martin.lau@linux.dev, song@kernel.org,
yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com,
ihor.solodrai@linux.dev, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] bpf: cgroup: fix null-ptr-deref in __cgroup_bpf_attach
Date: Wed, 2 Sep 2026 17:41:34 +0800 [thread overview]
Message-ID: <286de7d2-3750-4a44-a8e8-7054c8cf51d9@linux.dev> (raw)
In-Reply-To: <20260902090220.16395-1-liujing@cmss.chinamobile.com>
on 9/2/26 5:02 PM, Liu Jing wrote:
> In __cgroup_bpf_attach(), the expression "prog ? : link->link.prog"
> dereferences link before validating that link is non-NULL. If both
> prog and link are NULL (a contract violation by the caller), this
> causes a null pointer dereference.
Both being NULL is unreachable, so the new check is dead code.
It's meaningless.
>
> Add a safe ternary fallback and a NULL check for new_prog before
> it is used further.
>
> Signed-off-by: Liu Jing <liujing@cmss.chinamobile.com>
> ---
> kernel/bpf/cgroup.c | 4 +++-
> 1 file changed, 3 insertion(+), 1 deletion(-)
>
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -814,7 +814,7 @@
> struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
> struct bpf_cgroup_storage *new_storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
> struct bpf_cgroup_storage *old_storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
> - struct bpf_prog *new_prog = prog ? : link->link.prog;
> + struct bpf_prog *new_prog = prog ? : (link ? link->link.prog : NULL);
> enum cgroup_bpf_attach_type atype;
> u32 old_flags, old_pl_flags;
> struct bpf_prog_list *pl;
> @@ -833,6 +833,8 @@
> return -EINVAL;
> if (!!replace_prog != !!(flags & BPF_F_REPLACE))
> /* replace_prog implies BPF_F_REPLACE, and vice versa */
> + return -EINVAL;
> + if (!new_prog)
> return -EINVAL;
>
> atype = bpf_cgroup_atype_find(type, new_prog->aux->attach_btf_id);
>
> --
> 2.43.0
next prev parent reply other threads:[~2026-09-02 9:41 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-02 9:02 Liu Jing
2026-09-02 9:41 ` Jiayuan Chen [this message]
2026-09-08 16:00 ` Emil Tsalapatis
2026-09-02 9:52 ` bot+bpf-ci
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