CVE-2025-21938 (GCVE-0-2025-21938)
Vulnerability from cvelistv5
Published
2025-04-01 15:41
Modified
2026-08-05 11:55
Severity ?
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Summary
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: d045b9eb95a9b611c483897a69e7285aefdc66d7
Version: d045b9eb95a9b611c483897a69e7285aefdc66d7
Version: d045b9eb95a9b611c483897a69e7285aefdc66d7
Version: d045b9eb95a9b611c483897a69e7285aefdc66d7
Version: d045b9eb95a9b611c483897a69e7285aefdc66d7
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fix \u0027scheduling while atomic\u0027 in mptcp_pm_nl_append_new_local_addr\n\nIf multiple connection requests attempt to create an implicit mptcp\nendpoint in parallel, more than one caller may end up in\nmptcp_pm_nl_append_new_local_addr because none found the address in\nlocal_addr_list during their call to mptcp_pm_nl_get_local_id.  In this\ncase, the concurrent new_local_addr calls may delete the address entry\ncreated by the previous caller.  These deletes use synchronize_rcu, but\nthis is not permitted in some of the contexts where this function may be\ncalled.  During packet recv, the caller may be in a rcu read critical\nsection and have preemption disabled.\n\nAn example stack:\n\n   BUG: scheduling while atomic: swapper/2/0/0x00000302\n\n   Call Trace:\n   \u003cIRQ\u003e\n   dump_stack_lvl (lib/dump_stack.c:117 (discriminator 1))\n   dump_stack (lib/dump_stack.c:124)\n   __schedule_bug (kernel/sched/core.c:5943)\n   schedule_debug.constprop.0 (arch/x86/include/asm/preempt.h:33 kernel/sched/core.c:5970)\n   __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)\n   schedule (arch/x86/include/asm/preempt.h:84 kernel/sched/core.c:6804 kernel/sched/core.c:6818)\n   schedule_timeout (kernel/time/timer.c:2160)\n   wait_for_completion (kernel/sched/completion.c:96 kernel/sched/completion.c:116 kernel/sched/completion.c:127 kernel/sched/completion.c:148)\n   __wait_rcu_gp (include/linux/rcupdate.h:311 kernel/rcu/update.c:444)\n   synchronize_rcu (kernel/rcu/tree.c:3609)\n   mptcp_pm_nl_append_new_local_addr (net/mptcp/pm_netlink.c:966 net/mptcp/pm_netlink.c:1061)\n   mptcp_pm_nl_get_local_id (net/mptcp/pm_netlink.c:1164)\n   mptcp_pm_get_local_id (net/mptcp/pm.c:420)\n   subflow_check_req (net/mptcp/subflow.c:98 net/mptcp/subflow.c:213)\n   subflow_v4_route_req (net/mptcp/subflow.c:305)\n   tcp_conn_request (net/ipv4/tcp_input.c:7216)\n   subflow_v4_conn_request (net/mptcp/subflow.c:651)\n   tcp_rcv_state_process (net/ipv4/tcp_input.c:6709)\n   tcp_v4_do_rcv (net/ipv4/tcp_ipv4.c:1934)\n   tcp_v4_rcv (net/ipv4/tcp_ipv4.c:2334)\n   ip_protocol_deliver_rcu (net/ipv4/ip_input.c:205 (discriminator 1))\n   ip_local_deliver_finish (include/linux/rcupdate.h:813 net/ipv4/ip_input.c:234)\n   ip_local_deliver (include/linux/netfilter.h:314 include/linux/netfilter.h:308 net/ipv4/ip_input.c:254)\n   ip_sublist_rcv_finish (include/net/dst.h:461 net/ipv4/ip_input.c:580)\n   ip_sublist_rcv (net/ipv4/ip_input.c:640)\n   ip_list_rcv (net/ipv4/ip_input.c:675)\n   __netif_receive_skb_list_core (net/core/dev.c:5583 net/core/dev.c:5631)\n   netif_receive_skb_list_internal (net/core/dev.c:5685 net/core/dev.c:5774)\n   napi_complete_done (include/linux/list.h:37 include/net/gro.h:449 include/net/gro.h:444 net/core/dev.c:6114)\n   igb_poll (drivers/net/ethernet/intel/igb/igb_main.c:8244) igb\n   __napi_poll (net/core/dev.c:6582)\n   net_rx_action (net/core/dev.c:6653 net/core/dev.c:6787)\n   handle_softirqs (kernel/softirq.c:553)\n   __irq_exit_rcu (kernel/softirq.c:588 kernel/softirq.c:427 kernel/softirq.c:636)\n   irq_exit_rcu (kernel/softirq.c:651)\n   common_interrupt (arch/x86/kernel/irq.c:247 (discriminator 14))\n   \u003c/IRQ\u003e\n\nThis problem seems particularly prevalent if the user advertises an\nendpoint that has a different external vs internal address.  In the case\nwhere the external address is advertised and multiple connections\nalready exist, multiple subflow SYNs arrive in parallel which tends to\ntrigger the race during creation of the first local_addr_list entries\nwhich have the internal address instead.\n\nFix by skipping the replacement of an existing implicit local address if\ncalled via mptcp_pm_nl_get_local_id."
        }
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        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
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            {
              "lang": "en",
              "value": "AV:N - The vulnerable code executes directly in the TCP receive softirq path from a remote peer\u0027s MP_JOIN SYN packet (`tcp_v4_rcv` \u2192 `subflow_v4_conn_request` \u2192 `subflow_check_req` \u2192 `mptcp_pm_nl_get_local_id`). Any host able to reach an MPTCP listener over the network can drive it.\nAC:L - The attacker controls both sides of the race by emitting a burst of parallel MP_JOIN SYNs with distinct source ports, which RSS spreads across CPUs so multiple callers miss `__lookup_addr()` simultaneously; the commit states this race \"tends to trigger\" naturally under ordinary parallel subflow setup.\nPR:N - The only prerequisite is a valid MPTCP token, which any unauthenticated client obtains simply by completing an MP_CAPABLE handshake with the public listener. The vulnerable call happens in `subflow_check_req` before HMAC validation and before `mptcp_can_accept_new_subflow()`, so no kernel capability or application credential is involved.\nUI:N - The attacker only needs to send packets to a running MPTCP-enabled service; no action by any local user or administrator is required.\nS:U - The fault and its consequences are confined to the kernel\u0027s own security authority \u2014 the scheduler and RCU state of the affected host \u2014 with no crossing into a hypervisor, IOMMU, or other authority.\nC:N - This is a sleeping-in-atomic-context defect, not a memory-safety error; the endpoint teardown uses correct `list_del_rcu`/grace-period/free ordering under `pernet-\u003elock`, so no kernel memory is disclosed to the attacker.\nI:N - No out-of-bounds or use-after-free write primitive arises \u2014 the address-list entry replacement is fully serialized by `pernet-\u003elock` and the id bitmap accounting stays consistent, so the attacker gains no ability to modify kernel data.\nA:H - `synchronize_rcu()` runs from softirq with preemption disabled, producing a \"scheduling while atomic\" BUG and an illegal context switch off the idle task; under PREEMPT_RCU it is a self-deadlock because the blocked task is itself the RCU reader holding up the grace period, hanging the CPU and stalling RCU (kernel panic with `panic_on_rcu_stall`)."
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      "references": [
        {
          "url": "https://git.kernel.org/stable/c/f1404f368c40fc6a068dad72e4ee0824ee6a78ee"
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        {
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          "url": "https://git.kernel.org/stable/c/022bfe24aad8937705704ff2e414b100cf0f2e1a"
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      "title": "mptcp: fix \u0027scheduling while atomic\u0027 in mptcp_pm_nl_append_new_local_addr",
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    "cveId": "CVE-2025-21938",
    "datePublished": "2025-04-01T15:41:04.886Z",
    "dateReserved": "2024-12-29T08:45:45.789Z",
    "dateUpdated": "2026-08-05T11:55:28.260Z",
    "state": "PUBLISHED"
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