Message-ID: <2025040134-CVE-2025-21938-3b75@gregkh>
Date: Tue,  1 Apr 2025 16:40:02 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21938: mptcp: fix 'scheduling while atomic' in mptcp_pm_nl_append_new_local_addr

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

mptcp: fix 'scheduling while atomic' in mptcp_pm_nl_append_new_local_addr

If multiple connection requests attempt to create an implicit mptcp
endpoint in parallel, more than one caller may end up in
mptcp_pm_nl_append_new_local_addr because none found the address in
local_addr_list during their call to mptcp_pm_nl_get_local_id.  In this
case, the concurrent new_local_addr calls may delete the address entry
created by the previous caller.  These deletes use synchronize_rcu, but
this is not permitted in some of the contexts where this function may be
called.  During packet recv, the caller may be in a rcu read critical
section and have preemption disabled.

An example stack:

   BUG: scheduling while atomic: swapper/2/0/0x00000302

   Call Trace:
   <IRQ>
   dump_stack_lvl (lib/dump_stack.c:117 (discriminator 1))
   dump_stack (lib/dump_stack.c:124)
   __schedule_bug (kernel/sched/core.c:5943)
   schedule_debug.constprop.0 (arch/x86/include/asm/preempt.h:33 kernel/sched/core.c:5970)
   __schedule (arch/x86/include/asm/jump_label.h:27 include/linux/jump_label.h:207 kernel/sched/features.h:29 kernel/sched/core.c:6621)
   schedule (arch/x86/include/asm/preempt.h:84 kernel/sched/core.c:6804 kernel/sched/core.c:6818)
   schedule_timeout (kernel/time/timer.c:2160)
   wait_for_completion (kernel/sched/completion.c:96 kernel/sched/completion.c:116 kernel/sched/completion.c:127 kernel/sched/completion.c:148)
   __wait_rcu_gp (include/linux/rcupdate.h:311 kernel/rcu/update.c:444)
   synchronize_rcu (kernel/rcu/tree.c:3609)
   mptcp_pm_nl_append_new_local_addr (net/mptcp/pm_netlink.c:966 net/mptcp/pm_netlink.c:1061)
   mptcp_pm_nl_get_local_id (net/mptcp/pm_netlink.c:1164)
   mptcp_pm_get_local_id (net/mptcp/pm.c:420)
   subflow_check_req (net/mptcp/subflow.c:98 net/mptcp/subflow.c:213)
   subflow_v4_route_req (net/mptcp/subflow.c:305)
   tcp_conn_request (net/ipv4/tcp_input.c:7216)
   subflow_v4_conn_request (net/mptcp/subflow.c:651)
   tcp_rcv_state_process (net/ipv4/tcp_input.c:6709)
   tcp_v4_do_rcv (net/ipv4/tcp_ipv4.c:1934)
   tcp_v4_rcv (net/ipv4/tcp_ipv4.c:2334)
   ip_protocol_deliver_rcu (net/ipv4/ip_input.c:205 (discriminator 1))
   ip_local_deliver_finish (include/linux/rcupdate.h:813 net/ipv4/ip_input.c:234)
   ip_local_deliver (include/linux/netfilter.h:314 include/linux/netfilter.h:308 net/ipv4/ip_input.c:254)
   ip_sublist_rcv_finish (include/net/dst.h:461 net/ipv4/ip_input.c:580)
   ip_sublist_rcv (net/ipv4/ip_input.c:640)
   ip_list_rcv (net/ipv4/ip_input.c:675)
   __netif_receive_skb_list_core (net/core/dev.c:5583 net/core/dev.c:5631)
   netif_receive_skb_list_internal (net/core/dev.c:5685 net/core/dev.c:5774)
   napi_complete_done (include/linux/list.h:37 include/net/gro.h:449 include/net/gro.h:444 net/core/dev.c:6114)
   igb_poll (drivers/net/ethernet/intel/igb/igb_main.c:8244) igb
   __napi_poll (net/core/dev.c:6582)
   net_rx_action (net/core/dev.c:6653 net/core/dev.c:6787)
   handle_softirqs (kernel/softirq.c:553)
   __irq_exit_rcu (kernel/softirq.c:588 kernel/softirq.c:427 kernel/softirq.c:636)
   irq_exit_rcu (kernel/softirq.c:651)
   common_interrupt (arch/x86/kernel/irq.c:247 (discriminator 14))
   </IRQ>

This problem seems particularly prevalent if the user advertises an
endpoint that has a different external vs internal address.  In the case
where the external address is advertised and multiple connections
already exist, multiple subflow SYNs arrive in parallel which tends to
trigger the race during creation of the first local_addr_list entries
which have the internal address instead.

Fix by skipping the replacement of an existing implicit local address if
called via mptcp_pm_nl_get_local_id.

The Linux kernel CVE team has assigned CVE-2025-21938 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.18 with commit d045b9eb95a9b611c483897a69e7285aefdc66d7 and fixed in 6.1.131 with commit f1404f368c40fc6a068dad72e4ee0824ee6a78ee
	Issue introduced in 5.18 with commit d045b9eb95a9b611c483897a69e7285aefdc66d7 and fixed in 6.6.83 with commit f3fcdb2de9fdbed9d8c6a8eb2c5fbd7d6f54a4d8
	Issue introduced in 5.18 with commit d045b9eb95a9b611c483897a69e7285aefdc66d7 and fixed in 6.12.19 with commit 4b228dae3d2cc6d9dce167449cd8fa9f028e9376
	Issue introduced in 5.18 with commit d045b9eb95a9b611c483897a69e7285aefdc66d7 and fixed in 6.13.7 with commit 125ccafe6dd062901b5a0c31ee9038740fc8859e
	Issue introduced in 5.18 with commit d045b9eb95a9b611c483897a69e7285aefdc66d7 and fixed in 6.14 with commit 022bfe24aad8937705704ff2e414b100cf0f2e1a

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-21938
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/mptcp/pm_netlink.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/f1404f368c40fc6a068dad72e4ee0824ee6a78ee
	https://git.kernel.org/stable/c/f3fcdb2de9fdbed9d8c6a8eb2c5fbd7d6f54a4d8
	https://git.kernel.org/stable/c/4b228dae3d2cc6d9dce167449cd8fa9f028e9376
	https://git.kernel.org/stable/c/125ccafe6dd062901b5a0c31ee9038740fc8859e
	https://git.kernel.org/stable/c/022bfe24aad8937705704ff2e414b100cf0f2e1a

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