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From: "Jiayuan Chen" Message-ID: <78ee737400721758fa67b4f285e8ba61dc6b893b@linux.dev> TLS-Required: No Subject: Re: [PATCH bpf-next v2 1/3] bpf, sockmap: avoid using sk_socket after free To: "Michal Luczaj" , xiyou.wangcong@gmail.com, john.fastabend@gmail.com, jakub@cloudflare.com, martin.lau@linux.dev Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, andrii@kernel.org, eddyz87@gmail.com, mykolal@fb.com, ast@kernel.org, daniel@iogearbox.net, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, shuah@kernel.org, sgarzare@redhat.com, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, mrpre@163.com, cong.wang@bytedance.com, syzbot+dd90a702f518e0eac072@syzkaller.appspotmail.com In-Reply-To: References: <20250228055106.58071-1-jiayuan.chen@linux.dev> <20250228055106.58071-2-jiayuan.chen@linux.dev> X-Migadu-Flow: FLOW_OUT March 7, 2025 at 5:45 PM, "Michal Luczaj" wrote: >=20 >=20On 2/28/25 06:51, Jiayuan Chen wrote: >=20 >=20>=20 >=20> ... > >=20 >=20> static void sk_psock_verdict_data_ready(struct sock *sk) > >=20 >=20> { > >=20 >=20> - struct socket *sock =3D sk->sk_socket; > >=20 >=20> + struct socket *sock; > >=20 >=20> const struct proto_ops *ops; > >=20 >=20> int copied; > >=20 >=20>=20=20 >=20>=20 >=20> trace_sk_data_ready(sk); > >=20 >=20>=20=20 >=20>=20 >=20> + /* We need RCU to prevent the sk_socket from being released. > >=20 >=20> + * Especially for Unix sockets, we are currently in the process > >=20 >=20> + * context and do not have RCU protection. > >=20 >=20> + */ > >=20 >=20> + rcu_read_lock(); > >=20 >=20> + sock =3D sk->sk_socket; > >=20 >=20> if (unlikely(!sock)) > >=20 >=20> - return; > >=20 >=20> + goto unlock; > >=20 >=20> + > >=20 >=20> ops =3D READ_ONCE(sock->ops); > >=20 >=20> if (!ops || !ops->read_skb) > >=20 >=20> - return; > >=20 >=20> + goto unlock; > >=20 >=20> + > >=20 >=20> copied =3D ops->read_skb(sk, sk_psock_verdict_recv); > >=20 >=20> if (copied >=3D 0) { > >=20 >=20> struct sk_psock *psock; > >=20 >=20>=20=20 >=20>=20 >=20> - rcu_read_lock(); > >=20 >=20> psock =3D sk_psock(sk); > >=20 >=20> if (psock) > >=20 >=20> sk_psock_data_ready(sk, psock); > >=20 >=20> - rcu_read_unlock(); > >=20 >=20> } > >=20 >=20> +unlock: > >=20 >=20> + rcu_read_unlock(); > >=20 >=20> } > >=20 >=20 > Hi, >=20 >=20Doesn't sk_psock_handle_skb() (!ingress path) have the same `struct s= ocket` >=20 >=20release race issue? Any plans on fixing that one, too? Yes, the send path logic also has similar issues, and after some hacking, I was able to reproduce it. Thanks for providing this information. I can fix these together in the next revision of this patchset, anyway, this patchset still needs further confirmation from the maintainer. >=20 >=20BTW, lockdep (CONFIG_LOCKDEP=3Dy) complains about calling AF_UNIX's >=20 >=20read_skb() under RCU read lock. >=20 >=20Thanks, >=20 >=20Michal > My environment also has LOCKDEP enabled, but I didn't see similar warnings. Moreover, RCU assertions are typically written as: WARN_ON_ONCE(!rcu_read_lock_held()) And when LOCKDEP is not enabled, rcu_read_lock_held() defaults to returning 1. So, it's unlikely to trigger a warning due to an RCU lock being held. Could you provide more of the call stack? Thanks.