CVE-2026-64541 (GCVE-0-2026-64541)
Vulnerability from cvelistv5
Published
2026-07-27 20:10
Modified
2026-08-17 04:57
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 UAF in smc_cdc_rx_handler() by pinning the socket smc_cdc_rx_handler() looks up the connection by token under the link group's conns_lock, drops the lock, and then dereferences conn and the smc_sock derived from it, ending in sock_hold(&smc->sk) inside smc_cdc_msg_recv(). No reference is held across the lock release. The only reference pinning the socket while the connection is discoverable in the link group is taken in smc_lgr_register_conn() (sock_hold) and dropped in __smc_lgr_unregister_conn() (sock_put), both under conns_lock. Once the handler drops conns_lock, a concurrent close() -> smc_release() -> smc_conn_free() -> smc_lgr_unregister_conn() can drop that reference and free the smc_sock, so the handler's later sock_hold() runs on freed memory: WARNING: lib/refcount.c:25 at refcount_warn_saturate Workqueue: rxe_wq do_work refcount_warn_saturate (lib/refcount.c:25) smc_cdc_msg_recv (net/smc/smc_cdc.c:430) smc_cdc_rx_handler (net/smc/smc_cdc.c:502) smc_wr_rx_tasklet_fn (net/smc/smc_wr.c:445) tasklet_action_common (kernel/softirq.c:938) handle_softirqs (kernel/softirq.c:622) Kernel panic - not syncing: panic_on_warn set Only SMC-R is affected. The SMC-D receive tasklet is stopped by tasklet_kill(&conn->rx_tsklet) in smc_conn_free() before the connection is unregistered, so it cannot run concurrently with the free. Take the socket reference while still holding conns_lock, so the registration reference can no longer be the last one, and drop it once the handler is done.
References
Impacted products
Vendor Product Version
Linux Linux Version: d7b0e37c1ac152905b18a5b9506179091a35b0b6
Version: d7b0e37c1ac152905b18a5b9506179091a35b0b6
Version: d7b0e37c1ac152905b18a5b9506179091a35b0b6
Version: d7b0e37c1ac152905b18a5b9506179091a35b0b6
Version: d7b0e37c1ac152905b18a5b9506179091a35b0b6
Version: d7b0e37c1ac152905b18a5b9506179091a35b0b6
Version: d7b0e37c1ac152905b18a5b9506179091a35b0b6
Version: d7b0e37c1ac152905b18a5b9506179091a35b0b6
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{
  "containers": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/smc/smc_cdc.c"
          ],
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          "vendor": "Linux",
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        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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              "version": "0",
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              "version": "5.10.261",
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              "status": "unaffected",
              "version": "5.15.212",
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              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.178",
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              "version": "7.1.5",
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              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket\n\nsmc_cdc_rx_handler() looks up the connection by token under the link\ngroup\u0027s conns_lock, drops the lock, and then dereferences conn and the\nsmc_sock derived from it, ending in sock_hold(\u0026smc-\u003esk) inside\nsmc_cdc_msg_recv(). No reference is held across the lock release.\n\nThe only reference pinning the socket while the connection is\ndiscoverable in the link group is taken in smc_lgr_register_conn()\n(sock_hold) and dropped in __smc_lgr_unregister_conn() (sock_put), both\nunder conns_lock. Once the handler drops conns_lock, a concurrent\nclose() -\u003e smc_release() -\u003e smc_conn_free() -\u003e smc_lgr_unregister_conn()\ncan drop that reference and free the smc_sock, so the handler\u0027s later\nsock_hold() runs on freed memory:\n\n  WARNING: lib/refcount.c:25 at refcount_warn_saturate\n  Workqueue: rxe_wq do_work\n   refcount_warn_saturate (lib/refcount.c:25)\n   smc_cdc_msg_recv (net/smc/smc_cdc.c:430)\n   smc_cdc_rx_handler (net/smc/smc_cdc.c:502)\n   smc_wr_rx_tasklet_fn (net/smc/smc_wr.c:445)\n   tasklet_action_common (kernel/softirq.c:938)\n   handle_softirqs (kernel/softirq.c:622)\n  Kernel panic - not syncing: panic_on_warn set\n\nOnly SMC-R is affected. The SMC-D receive tasklet is stopped by\ntasklet_kill(\u0026conn-\u003erx_tsklet) in smc_conn_free() before the connection\nis unregistered, so it cannot run concurrently with the free.\n\nTake the socket reference while still holding conns_lock, so the\nregistration reference can no longer be the last one, and drop it once\nthe handler is done."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The vulnerable handler is driven entirely by a CDC control message sent by the remote SMC-R peer over the RDMA link, with an attacker-chosen `token` field and no local syscall involvement. SMC-R runs over RoCEv2 (IP/UDP-routable, port 4791) with the CLC handshake over plain TCP, and SMC-Rv2 explicitly supports non-local/routed peers, so the attacker need not share an L2 segment.\nAC:L - The attacker controls both sides of the race: it chooses when to emit CDC messages and which connection to target (the alert token is disclosed to it in the CLC accept/confirm), and it can drive the teardown side itself via CDC close/abort flags into `smc_close_passive_work()` or a stale seqno with `failover_validation` into `abort_work` -\u003e `smc_conn_kill()`. The race can be retried indefinitely across many connections in the same link group, and was reproduced in practice with soft-RoCE.\nPR:N - Establishing an SMC-R connection to a listening SMC socket requires no credentials \u2014 SMC has no authentication layer of its own, exactly like plain TCP. Everything after connection establishment (sending CDC messages with a chosen token, signalling close/abort) is available to an unauthenticated peer.\nUI:N - The CDC message is processed in a softirq tasklet from the RDMA completion queue with no involvement from any local user or application action. No victim interaction of any kind is needed.\nS:U - The corruption is confined to kernel memory within the same security authority; there is no VM, IOMMU, or sandbox boundary crossed. This is a standard in-kernel use-after-free.\nC:H - The freed `smc_sock` is reused type-safely as another live socket, so attacker-supplied cursors applied by `smc_cdc_msg_recv_action()` break the `0 \u003c= bytes_to_rcv \u003c= rmb_desc-\u003elen` invariant and make `smc_rx_recvmsg()` hand stale RMB contents to userspace, while the urgent-data path reads `*(base + conn-\u003eurg_curs.count - 1)` at an attacker-chosen offset. Once the slab page is reclaimed after the RCU grace period, reuse is unconstrained, giving a general kernel-memory read primitive.\nI:H - `sock_hold()` on an already-zero refcount followed by `sock_put()` re-enters `sk_free()`, yielding a double free, and the handler additionally writes `sk_err`/`sk_shutdown`, makes indirect calls through `sk_data_ready()`/`sk_write_space()`, and `queue_work()`s a freed `work_struct`. These are classic heap-spray and control-flow-hijack primitives leading to arbitrary kernel write.\nA:H - The reported symptom is `refcount_warn_saturate` from `smc_cdc_msg_recv()`, which is an immediate kernel panic on `panic_on_warn` systems, and dereferencing freed memory in softirq context otherwise oopses. The attacker can trigger it repeatedly without authentication."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:57:17.774Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/8de4f665d0febfb92803dece377791a563fc7041"
        },
        {
          "url": "https://git.kernel.org/stable/c/8145b432136285e01091815b48ceb2dae261f262"
        },
        {
          "url": "https://git.kernel.org/stable/c/1951bffbc6493ec34cff3956b29d4bc6606904a6"
        },
        {
          "url": "https://git.kernel.org/stable/c/647b19e5cc145a2f1f685ae8ff3805a17356888c"
        },
        {
          "url": "https://git.kernel.org/stable/c/472e9d7c0d5b03be3ff91ff941f57da822b031bc"
        },
        {
          "url": "https://git.kernel.org/stable/c/3bfb96d9bc6a7ed0b99c7db329cc2e22a28d84bb"
        },
        {
          "url": "https://git.kernel.org/stable/c/ce5aa8084329351086894aa34d77e40301d5bd3d"
        },
        {
          "url": "https://git.kernel.org/stable/c/9d160b35cc34a2ba8229d07651468a7848325135"
        }
      ],
      "title": "net/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64541",
    "datePublished": "2026-07-27T20:10:34.439Z",
    "dateReserved": "2026-07-19T15:36:31.795Z",
    "dateUpdated": "2026-08-17T04:57:17.774Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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