Re: [PATCH bpf-next v1 1/3] bpf, sockmap: avoid using sk_socket after free

[Cong Wang]

On Wed, Feb 26, 2025 at 09:22:40PM +0800, Jiayuan Chen wrote:
> Use RCU lock to protect sk_socket, preventing concurrent close and release
> by another thread.
> 
> Because TCP/UDP are already within a relatively large critical section:
> '''
> ip_local_deliver_finish
>   rcu_read_lock
>   ip_protocol_deliver_rcu
>       tcp_rcv/udp_rcv
>   rcu_read_unlock
> '''
> 
> Adding rcu_read_{un}lock() at the entrance and exit of sk_data_ready
> will not increase performance overhead.
> 
> Reported-by: syzbot+dd90a702f518e0eac072@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/bpf/6734c033.050a0220.2a2fcc.0015.GAE@xxxxxxxxxx/
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>

sock_def_readable() already acquires RCU read lock anyway.

Reviewed-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>

Thanks!