mptcp: pm: Fix uaf in __timer_delete_sync

Vulnerability Description

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.

References

• https://git.kernel.org/stable/c/0e7814b028cd50b3ff79659d23dfa9da6a1e75e1
• https://git.kernel.org/stable/c/3554482f4691571fc4b5490c17ae26896e62171c
• https://git.kernel.org/stable/c/67409b358500c71632116356a0b065f112d7b707
• https://git.kernel.org/stable/c/6452b162549c7f9ef54655d3fb9977b9192e6e5b
• https://git.kernel.org/stable/c/12134a652b0a10064844ea235173e70246eba6dc
• https://git.kernel.org/stable/c/b4cd80b0338945a94972ac3ed54f8338d2da2076