In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: Fix uaf in __timer_delete_sync There are two paths to access mptcp_pm_del_add_timer, result in a race condition: CPU1 CPU2 ==== ==== net_rx_action napi_poll netlink_sendmsg __napi_poll netlink_unicast process_backlog netlink_unicast_kernel __netif_receive_skb genl_rcv __netif_receive_skb_one_core netlink_rcv_skb NF_HOOK genl_rcv_msg ip_local_deliver_finish genl_family_rcv_msg ip_protocol_deliver_rcu genl_family_rcv_msg_doit tcp_v4_rcv mptcp_pm_nl_flush_addrs_doit tcp_v4_do_rcv mptcp_nl_remove_addrs_list tcp_rcv_established mptcp_pm_remove_addrs_and_subflows tcp_data_queue remove_anno_list_by_saddr mptcp_incoming_options mptcp_pm_del_add_timer mptcp_pm_del_add_timer kfree(entry) In remove_anno_list_by_saddr(running on CPU2), after leaving the critical zone protected by "pm.lock", the entry will be released, which leads to the occurrence of uaf in the mptcp_pm_del_add_timer(running on CPU1). Keeping a reference to add_timer inside the lock, and calling sk_stop_timer_sync() with this reference, instead of "entry->add_timer". Move list_del(&entry->list) to mptcp_pm_del_add_timer and inside the pm lock, do not directly access any members of the entry outside the pm lock, which can avoid similar "entry->x" uaf.
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.