CVE-2024-46858

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.