CVE-2026-98253 (GCVE-0-2026-98253)
Vulnerability from cvelistv5
Published
2026-10-06 08:45
Modified
2026-10-19 09:16
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: RDMA/ucma: Serialize join and leave on copy_to_user failure rdma_join_multicast() queues RoCE work that later reads the ucma_multicast through event->param.ud.private_data, then list_add()s the CMA multicast at the head of id_priv->mc_list. rdma_leave_multicast() matches only by sockaddr and destroys the first hit. ucma_process_join() used to drop ctx->mutex after a successful join and retake it only if copy_to_user() failed. Two concurrent JOIN_MCAST calls with the same address can therefore insert a second CMA entry before the first thread's leave. leave then cancels the newer work and the older worker still dereferences the ucma_multicast that the first thread frees. Keep ctx->mutex held from rdma_join_multicast() through copy_to_user() and, on -EFAULT, through rdma_leave_multicast() so leave cannot miss this join. Do not leave if join itself failed: that path never published this address on mc_list, and a leave-by-addr would destroy an earlier successful join.
References
Impacted products
Vendor Product Version
Linux Linux Version: 60d613b39e8d0c9f3b526e9c96445422b4562d76
Version: fe454dc31e84f8c14cb8942fcb61666c9f40745b
Version: fe454dc31e84f8c14cb8942fcb61666c9f40745b
Version: fe454dc31e84f8c14cb8942fcb61666c9f40745b
Version: fe454dc31e84f8c14cb8942fcb61666c9f40745b
Version: fe454dc31e84f8c14cb8942fcb61666c9f40745b
Version: fe454dc31e84f8c14cb8942fcb61666c9f40745b
Version: fe454dc31e84f8c14cb8942fcb61666c9f40745b
Version: a3262b3884dd67b4c5632ce7cdf9cff9d1a575d4
Version: 5.10.20   ≤
Version: 5.11.3   ≤
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/infiniband/core/ucma.c"
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          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
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          ],
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          "vendor": "Linux",
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            },
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              "lessThanOrEqual": "6.18.*",
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              "versionType": "original_commit_for_fix"
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      "cpeApplicability": [
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          "nodes": [
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                  "vulnerable": true
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nRDMA/ucma: Serialize join and leave on copy_to_user failure\n\nrdma_join_multicast() queues RoCE work that later reads the ucma_multicast\nthrough event-\u003eparam.ud.private_data, then list_add()s the CMA multicast\nat the head of id_priv-\u003emc_list. rdma_leave_multicast() matches only by\nsockaddr and destroys the first hit.\n\nucma_process_join() used to drop ctx-\u003emutex after a successful join and\nretake it only if copy_to_user() failed. Two concurrent JOIN_MCAST calls\nwith the same address can therefore insert a second CMA entry before the\nfirst thread\u0027s leave. leave then cancels the newer work and the older\nworker still dereferences the ucma_multicast that the first thread frees.\n\nKeep ctx-\u003emutex held from rdma_join_multicast() through copy_to_user() and,\non -EFAULT, through rdma_leave_multicast() so leave cannot miss this join.\nDo not leave if join itself failed: that path never published this address\non mc_list, and a leave-by-addr would destroy an earlier successful join."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is reached by write() of RDMA_USER_CM_CMD_JOIN_MCAST/JOIN_IP_MCAST on the local char device /dev/infiniband/rdma_cm into ucma_process_join(). The trigger is local: two racing joins and a bad response pointer. No remote peer supplies the data that causes it, so AV:L.\nAC:L - The attacker drives every part of the race. They make copy_to_user() fail with a bad cmd-\u003eresponse pointer, and a second thread issues JOIN_MCAST for the same address while ctx-\u003emutex is dropped. rdma_leave_multicast() then destroys the newer mc_list head and cancels the wrong iboe_join work. The attempt can be repeated until it wins.\nPR:L - rdma_cm is created with mode 0666 and ucma_write() does no capability check. Any local user on a host with a RoCE port can create a UD cm_id, bind it and join multicast. An unprivileged user cannot create a soft-RoCE device, because nldev NEWLINK needs CAP_NET_ADMIN in the initial namespace, so the RoCE port must already exist.\nUI:N - The attacker triggers the bug entirely through their own writes on an rdma_cm file descriptor they opened. No other user or administrator has to act.\nS:U - The freed ucma_multicast and the corrupted kernel heap are in the same kernel security authority. This is local kernel memory corruption, not a VM or IOMMU boundary crossing.\nC:H - cma_iboe_join_work_handler() calls ucma_create_uevent() on the freed ucma_multicast, reading mc-\u003euid and mc-\u003eid into the event that GET_EVENT copies to userspace. If the freed slot is reclaimed with sprayed objects, this use-after-free gives a read primitive.\nI:H - uevent-\u003emc keeps a pointer to the freed ucma_multicast, and ucma_get_event() then runs uevent-\u003emc-\u003eevents_reported++. That is an attacker-timed write into freed and reclaimable slab memory, usable to corrupt an object sprayed into the slot.\nA:H - The use-after-free of ucma_multicast in the RoCE join worker and in ucma_get_event() can corrupt the slab or oops the kernel, crashing the host. Syzbot reported this bug (extid a6ffe86390c8a6afc818)."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:16:24.567Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/29b9ed83d8bfab5c6e11fcbf1aa836aa4ae26cb9"
        },
        {
          "url": "https://git.kernel.org/stable/c/52172e11bd074ccaded21740ffeb67123f01dd00"
        },
        {
          "url": "https://git.kernel.org/stable/c/01e29d0d78a8f66f221625720a04939eef5ec1f6"
        },
        {
          "url": "https://git.kernel.org/stable/c/ae805d204cf1f15b87d1bf3529b4c649f3519420"
        },
        {
          "url": "https://git.kernel.org/stable/c/43c4e24bd10370fc976f6220518049ce71419399"
        },
        {
          "url": "https://git.kernel.org/stable/c/01cbdb724c584d7772fd25af2e4dfdf8527ce0d5"
        },
        {
          "url": "https://git.kernel.org/stable/c/83610ee5e498fa5bfcb80031d2b959baea276bf6"
        },
        {
          "url": "https://git.kernel.org/stable/c/662ade4de9ff5eceb0820a9f8e9fac70ba6a815b"
        }
      ],
      "title": "RDMA/ucma: Serialize join and leave on copy_to_user failure",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98253",
    "datePublished": "2026-10-06T08:45:20.077Z",
    "dateReserved": "2026-09-25T10:25:14.331Z",
    "dateUpdated": "2026-10-19T09:16:24.567Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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