CVE-2024-56640 (GCVE-0-2024-56640)
Vulnerability from cvelistv5
Published
2024-12-27 15:02
Modified
2026-08-05 11:45
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net/smc: fix LGR and link use-after-free issue We encountered a LGR/link use-after-free issue, which manifested as the LGR/link refcnt reaching 0 early and entering the clear process, making resource access unsafe. refcount_t: addition on 0; use-after-free. WARNING: CPU: 14 PID: 107447 at lib/refcount.c:25 refcount_warn_saturate+0x9c/0x140 Workqueue: events smc_lgr_terminate_work [smc] Call trace: refcount_warn_saturate+0x9c/0x140 __smc_lgr_terminate.part.45+0x2a8/0x370 [smc] smc_lgr_terminate_work+0x28/0x30 [smc] process_one_work+0x1b8/0x420 worker_thread+0x158/0x510 kthread+0x114/0x118 or refcount_t: underflow; use-after-free. WARNING: CPU: 6 PID: 93140 at lib/refcount.c:28 refcount_warn_saturate+0xf0/0x140 Workqueue: smc_hs_wq smc_listen_work [smc] Call trace: refcount_warn_saturate+0xf0/0x140 smcr_link_put+0x1cc/0x1d8 [smc] smc_conn_free+0x110/0x1b0 [smc] smc_conn_abort+0x50/0x60 [smc] smc_listen_find_device+0x75c/0x790 [smc] smc_listen_work+0x368/0x8a0 [smc] process_one_work+0x1b8/0x420 worker_thread+0x158/0x510 kthread+0x114/0x118 It is caused by repeated release of LGR/link refcnt. One suspect is that smc_conn_free() is called repeatedly because some smc_conn_free() from server listening path are not protected by sock lock. e.g. Calls under socklock | smc_listen_work ------------------------------------------------------- lock_sock(sk) | smc_conn_abort smc_conn_free | \- smc_conn_free \- smcr_link_put | \- smcr_link_put (duplicated) release_sock(sk) So here add sock lock protection in smc_listen_work() path, making it exclusive with other connection operations.
References
Impacted products
Vendor Product Version
Linux Linux Version: 3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8
Version: 3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8
Version: 3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8
Version: 3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8
Version: 3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/smc: fix LGR and link use-after-free issue\n\nWe encountered a LGR/link use-after-free issue, which manifested as\nthe LGR/link refcnt reaching 0 early and entering the clear process,\nmaking resource access unsafe.\n\n refcount_t: addition on 0; use-after-free.\n WARNING: CPU: 14 PID: 107447 at lib/refcount.c:25 refcount_warn_saturate+0x9c/0x140\n Workqueue: events smc_lgr_terminate_work [smc]\n Call trace:\n  refcount_warn_saturate+0x9c/0x140\n  __smc_lgr_terminate.part.45+0x2a8/0x370 [smc]\n  smc_lgr_terminate_work+0x28/0x30 [smc]\n  process_one_work+0x1b8/0x420\n  worker_thread+0x158/0x510\n  kthread+0x114/0x118\n\nor\n\n refcount_t: underflow; use-after-free.\n WARNING: CPU: 6 PID: 93140 at lib/refcount.c:28 refcount_warn_saturate+0xf0/0x140\n Workqueue: smc_hs_wq smc_listen_work [smc]\n Call trace:\n  refcount_warn_saturate+0xf0/0x140\n  smcr_link_put+0x1cc/0x1d8 [smc]\n  smc_conn_free+0x110/0x1b0 [smc]\n  smc_conn_abort+0x50/0x60 [smc]\n  smc_listen_find_device+0x75c/0x790 [smc]\n  smc_listen_work+0x368/0x8a0 [smc]\n  process_one_work+0x1b8/0x420\n  worker_thread+0x158/0x510\n  kthread+0x114/0x118\n\nIt is caused by repeated release of LGR/link refcnt. One suspect is that\nsmc_conn_free() is called repeatedly because some smc_conn_free() from\nserver listening path are not protected by sock lock.\n\ne.g.\n\nCalls under socklock        | smc_listen_work\n-------------------------------------------------------\nlock_sock(sk)               | smc_conn_abort\nsmc_conn_free               | \\- smc_conn_free\n\\- smcr_link_put            |    \\- smcr_link_put (duplicated)\nrelease_sock(sk)\n\nSo here add sock lock protection in smc_listen_work() path, making it\nexclusive with other connection operations."
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              "value": "AV:N - The bug is in `smc_listen_work()`, the SMC server-side CLC handshake worker that is queued from `smc_tcp_listen_work()` for every inbound TCP connection carrying the SMC option, and it processes CLC Proposal/Confirm/Decline messages sent by the remote peer over routable TCP/IP. A remote host that can reach an AF_SMC listener drives the entire vulnerable path.\nAC:L - The attacker controls both sides of the race: `smc_clc_wait_msg()` (net/smc/smc_clc.c:784-794) accepts a CLC DECLINE at any point, and with the attacker-chosen `SMC_FIRST_CONTACT_MASK` bit set it calls `smc_lgr_terminate_sched()`, scheduling `__smc_lgr_terminate()` (which takes lock_sock and frees conn state) concurrently with the unlocked `smc_listen_work()` \u2192 `smc_conn_abort()` \u2192 `smc_conn_free()` path, whose `conn-\u003efreed` guard is an unsynchronized bitfield. The attacker can open unlimited parallel connections into the same link group on the separate `smc_hs_wq` and retry indefinitely at no cost.\nPR:N - The CLC handshake in `smc_listen_work()` runs entirely before any application-level authentication and requires no credentials \u2014 the attacker only needs to complete a TCP connection to the SMC listener. No capability, namespace, or local account is involved.\nUI:N - The listen worker is queued automatically from the TCP accept path by `smc_clcsock_data_ready()`/`smc_tcp_listen_work()`; no action by the local user or administrator is needed beyond running the SMC server that is already listening.\nS:U - The corruption is confined to kernel heap objects (`struct smc_link_group`, `struct smc_link`) within the same kernel security authority, with no crossing of a VM, IOMMU, or sandbox boundary.\nC:H - The duplicate `smcr_link_put()`/`smc_lgr_put()` drives the refcounts to zero early, so the `kzalloc`\u0027d `struct smc_link_group` is `kfree()`d while `__smc_lgr_terminate()`, `smc_listen_work()`, and the LLC/CDC paths still dereference it \u2014 a classic use-after-free read of a generic kmalloc slab object that an attacker can reallocate and shape, leaking link-group state including `peer_systemid` and RDMA `rtokens` (remote keys/addresses).\nI:H - Post-free writes into the reallocated object include `lgr-\u003esync_err`/`terminating` bitfields, `refcount_inc()`, and list/rb-tree manipulation, while the freed structure embeds `struct work_struct terminate_work`, `struct delayed_work free_work`, and per-link `link_down_wrk` \u2014 function pointers that `schedule_work()`/`smc_lgr_schedule_free_work()` will subsequently invoke, giving a heap-spray path to control-flow hijack.\nA:H - The commit documents real production `refcount_t: underflow`/`addition on 0` warnings in `smcr_link_put()` and `__smc_lgr_terminate()`; refcount saturation plus use of freed link-group memory yields oopses and kernel panics, and the condition is remotely and repeatably triggerable."
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    "cveId": "CVE-2024-56640",
    "datePublished": "2024-12-27T15:02:42.253Z",
    "dateReserved": "2024-12-27T15:00:39.839Z",
    "dateUpdated": "2026-08-05T11:45:38.986Z",
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A remote host that can reach an AF_SMC listener drives the entire vulnerable path.\\nAC:L - The attacker controls both sides of the race: `smc_clc_wait_msg()` (net/smc/smc_clc.c:784-794) accepts a CLC DECLINE at any point, and with the attacker-chosen `SMC_FIRST_CONTACT_MASK` bit set it calls `smc_lgr_terminate_sched()`, scheduling `__smc_lgr_terminate()` (which takes lock_sock and frees conn state) concurrently with the unlocked `smc_listen_work()` \\u2192 `smc_conn_abort()` \\u2192 `smc_conn_free()` path, whose `conn-\u003efreed` guard is an unsynchronized bitfield. The attacker can open unlimited parallel connections into the same link group on the separate `smc_hs_wq` and retry indefinitely at no cost.\\nPR:N - The CLC handshake in `smc_listen_work()` runs entirely before any application-level authentication and requires no credentials \\u2014 the attacker only needs to complete a TCP connection to the SMC listener. No capability, namespace, or local account is involved.\\nUI:N - The listen worker is queued automatically from the TCP accept path by `smc_clcsock_data_ready()`/`smc_tcp_listen_work()`; no action by the local user or administrator is needed beyond running the SMC server that is already listening.\\nS:U - The corruption is confined to kernel heap objects (`struct smc_link_group`, `struct smc_link`) within the same kernel security authority, with no crossing of a VM, IOMMU, or sandbox boundary.\\nC:H - The duplicate `smcr_link_put()`/`smc_lgr_put()` drives the refcounts to zero early, so the `kzalloc`\u0027d `struct smc_link_group` is `kfree()`d while `__smc_lgr_terminate()`, `smc_listen_work()`, and the LLC/CDC paths still dereference it \\u2014 a classic use-after-free read of a generic kmalloc slab object that an attacker can reallocate and shape, leaking link-group state including `peer_systemid` and RDMA `rtokens` (remote keys/addresses).\\nI:H - Post-free writes into the reallocated object include `lgr-\u003esync_err`/`terminating` bitfields, `refcount_inc()`, and list/rb-tree manipulation, while the freed structure embeds `struct work_struct terminate_work`, `struct delayed_work free_work`, and per-link `link_down_wrk` \\u2014 function pointers that `schedule_work()`/`smc_lgr_schedule_free_work()` will subsequently invoke, giving a heap-spray path to control-flow hijack.\\nA:H - The commit documents real production `refcount_t: underflow`/`addition on 0` warnings in `smcr_link_put()` and `__smc_lgr_terminate()`; refcount saturation plus use of freed link-group memory yields oopses and kernel panics, and the condition is remotely and repeatably triggerable.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8\", \"lessThan\": \"f502a88fdd415647a1f2dc45fac71b9c522a052b\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8\", \"lessThan\": \"0cf598548a6c36d90681d53c6b77d52363f2f295\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8\", \"lessThan\": \"673d606683ac70bc074ca6676b938bff18635226\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8\", \"lessThan\": \"6f0ae06a234a78ae137064f2c89135ac078a00eb\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"3b2dec2603d5b06ad3af71c1164ca0b92df3d2a8\", \"lessThan\": \"2c7f14ed9c19ec0f149479d1c2842ec1f9bf76d7\", \"versionType\": \"git\"}], \"programFiles\": [\"net/smc/af_smc.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"4.18\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"4.18\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.15.174\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.120\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.66\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.12.5\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.13\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"net/smc/af_smc.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/f502a88fdd415647a1f2dc45fac71b9c522a052b\"}, {\"url\": \"https://git.kernel.org/stable/c/0cf598548a6c36d90681d53c6b77d52363f2f295\"}, {\"url\": \"https://git.kernel.org/stable/c/673d606683ac70bc074ca6676b938bff18635226\"}, {\"url\": \"https://git.kernel.org/stable/c/6f0ae06a234a78ae137064f2c89135ac078a00eb\"}, {\"url\": \"https://git.kernel.org/stable/c/2c7f14ed9c19ec0f149479d1c2842ec1f9bf76d7\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nnet/smc: fix LGR and link use-after-free issue\\n\\nWe encountered a LGR/link use-after-free issue, which manifested as\\nthe LGR/link refcnt reaching 0 early and entering the clear process,\\nmaking resource access unsafe.\\n\\n refcount_t: addition on 0; use-after-free.\\n WARNING: CPU: 14 PID: 107447 at lib/refcount.c:25 refcount_warn_saturate+0x9c/0x140\\n Workqueue: events smc_lgr_terminate_work [smc]\\n Call trace:\\n  refcount_warn_saturate+0x9c/0x140\\n  __smc_lgr_terminate.part.45+0x2a8/0x370 [smc]\\n  smc_lgr_terminate_work+0x28/0x30 [smc]\\n  process_one_work+0x1b8/0x420\\n  worker_thread+0x158/0x510\\n  kthread+0x114/0x118\\n\\nor\\n\\n refcount_t: underflow; use-after-free.\\n WARNING: CPU: 6 PID: 93140 at lib/refcount.c:28 refcount_warn_saturate+0xf0/0x140\\n Workqueue: smc_hs_wq smc_listen_work [smc]\\n Call trace:\\n  refcount_warn_saturate+0xf0/0x140\\n  smcr_link_put+0x1cc/0x1d8 [smc]\\n  smc_conn_free+0x110/0x1b0 [smc]\\n  smc_conn_abort+0x50/0x60 [smc]\\n  smc_listen_find_device+0x75c/0x790 [smc]\\n  smc_listen_work+0x368/0x8a0 [smc]\\n  process_one_work+0x1b8/0x420\\n  worker_thread+0x158/0x510\\n  kthread+0x114/0x118\\n\\nIt is caused by repeated release of LGR/link refcnt. One suspect is that\\nsmc_conn_free() is called repeatedly because some smc_conn_free() from\\nserver listening path are not protected by sock lock.\\n\\ne.g.\\n\\nCalls under socklock        | smc_listen_work\\n-------------------------------------------------------\\nlock_sock(sk)               | smc_conn_abort\\nsmc_conn_free               | \\\\- smc_conn_free\\n\\\\- smcr_link_put            |    \\\\- smcr_link_put (duplicated)\\nrelease_sock(sk)\\n\\nSo here add sock lock protection in smc_listen_work() path, making it\\nexclusive with other connection operations.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.174\", \"versionStartIncluding\": \"4.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.120\", \"versionStartIncluding\": \"4.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.66\", \"versionStartIncluding\": \"4.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.5\", \"versionStartIncluding\": \"4.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.13\", \"versionStartIncluding\": \"4.18\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T11:45:38.986Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2024-56640\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T11:45:38.986Z\", \"dateReserved\": \"2024-12-27T15:00:39.839Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-12-27T15:02:42.253Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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