CVE-2025-38523 (GCVE-0-2025-38523)
Vulnerability from cvelistv5
Published
2025-08-16 11:12
Modified
2026-08-05 12:02
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: cifs: Fix the smbd_response slab to allow usercopy The handling of received data in the smbdirect client code involves using copy_to_iter() to copy data from the smbd_reponse struct's packet trailer to a folioq buffer provided by netfslib that encapsulates a chunk of pagecache. If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks then performed in copy_to_iter() oopsing with something like the following: CIFS: Attempting to mount //172.31.9.1/test CIFS: VFS: RDMA transport established usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)! ------------[ cut here ]------------ kernel BUG at mm/usercopy.c:102! ... RIP: 0010:usercopy_abort+0x6c/0x80 ... Call Trace: <TASK> __check_heap_object+0xe3/0x120 __check_object_size+0x4dc/0x6d0 smbd_recv+0x77f/0xfe0 [cifs] cifs_readv_from_socket+0x276/0x8f0 [cifs] cifs_read_from_socket+0xcd/0x120 [cifs] cifs_demultiplex_thread+0x7e9/0x2d50 [cifs] kthread+0x396/0x830 ret_from_fork+0x2b8/0x3b0 ret_from_fork_asm+0x1a/0x30 The problem is that the smbd_response slab's packet field isn't marked as being permitted for usercopy. Fix this by passing parameters to kmem_slab_create() to indicate that copy_to_iter() is permitted from the packet region of the smbd_response slab objects, less the header space.
References
Impacted products
Vendor Product Version
Linux Linux Version: ee4cdf7ba857a894ad1650d6ab77669cbbfa329e
Version: ee4cdf7ba857a894ad1650d6ab77669cbbfa329e
Version: ee4cdf7ba857a894ad1650d6ab77669cbbfa329e
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/smbdirect.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "87dcc7e33fc3dcb8ed32333cec016528b5bb6ce4",
              "status": "affected",
              "version": "ee4cdf7ba857a894ad1650d6ab77669cbbfa329e",
              "versionType": "git"
            },
            {
              "lessThan": "f0dd353d47f7051afa98c6c60c7486831eb1a410",
              "status": "affected",
              "version": "ee4cdf7ba857a894ad1650d6ab77669cbbfa329e",
              "versionType": "git"
            },
            {
              "lessThan": "43e7e284fc77b710d899569360ea46fa3374ae22",
              "status": "affected",
              "version": "ee4cdf7ba857a894ad1650d6ab77669cbbfa329e",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/smbdirect.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.12"
            },
            {
              "lessThan": "6.12",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.36",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.15.*",
              "status": "unaffected",
              "version": "6.15.8",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.16",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.36",
                  "versionStartIncluding": "6.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.15.8",
                  "versionStartIncluding": "6.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.16",
                  "versionStartIncluding": "6.12",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ncifs: Fix the smbd_response slab to allow usercopy\n\nThe handling of received data in the smbdirect client code involves using\ncopy_to_iter() to copy data from the smbd_reponse struct\u0027s packet trailer\nto a folioq buffer provided by netfslib that encapsulates a chunk of\npagecache.\n\nIf, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks\nthen performed in copy_to_iter() oopsing with something like the following:\n\n CIFS: Attempting to mount //172.31.9.1/test\n CIFS: VFS: RDMA transport established\n usercopy: Kernel memory exposure attempt detected from SLUB object \u0027smbd_response_0000000091e24ea1\u0027 (offset 81, size 63)!\n ------------[ cut here ]------------\n kernel BUG at mm/usercopy.c:102!\n ...\n RIP: 0010:usercopy_abort+0x6c/0x80\n ...\n Call Trace:\n  \u003cTASK\u003e\n  __check_heap_object+0xe3/0x120\n  __check_object_size+0x4dc/0x6d0\n  smbd_recv+0x77f/0xfe0 [cifs]\n  cifs_readv_from_socket+0x276/0x8f0 [cifs]\n  cifs_read_from_socket+0xcd/0x120 [cifs]\n  cifs_demultiplex_thread+0x7e9/0x2d50 [cifs]\n  kthread+0x396/0x830\n  ret_from_fork+0x2b8/0x3b0\n  ret_from_fork_asm+0x1a/0x30\n\nThe problem is that the smbd_response slab\u0027s packet field isn\u0027t marked as\nbeing permitted for usercopy.\n\nFix this by passing parameters to kmem_slab_create() to indicate that\ncopy_to_iter() is permitted from the packet region of the smbd_response\nslab objects, less the header space."
        }
      ],
      "metrics": [
        {
          "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",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The crash is driven entirely by data received from the remote SMB Direct peer in the CIFS client\u0027s transport receive path (`cifs_demultiplex_thread` \u2192 `smbd_recv`), and SMB Direct runs over iWARP/RoCEv2/soft-iWARP, which are routable over ordinary IP networks rather than confined to one L2 segment. A malicious or impersonated SMB server, or a MITM on the unauthenticated smbdirect transport headers, reaches the code remotely.\nAC:L - The failure is fully deterministic \u2014 the missing slab whitelist makes `__check_heap_object()` reject every single `copy_to_iter()` out of `smbd_response`, so the very first SMB2 response body over the connection panics the client with no race, timing, or memory-layout dependency. `CONFIG_HARDENED_USERCOPY` is a default-on distro hardening option and `CONFIG_CIFS_SMB_DIRECT` is a supported \"say Y\" option, so no rare configuration is needed within the RDMA/HPC/cloud-storage deployments that use this transport.\nPR:N - The attacker is the remote smbdirect peer and holds no privileges or credentials on the victim client; the oops fires while processing the SMB2 NEGOTIATE response, before session setup and authentication complete. Anything answering the client\u0027s SMBD connect on port 5445/445 can trigger it.\nUI:N - No human action is part of the attack \u2014 RDMA-backed CIFS mounts are established automatically from fstab/autofs/systemd units and the client auto-reconnects, a state an attacker can force simply by dropping the connection. The crash then occurs during ordinary automatic protocol negotiation.\nS:U - The `BUG()` and its consequences are confined to the kernel of the affected client host, with no crossing into another security authority such as a hypervisor, IOMMU, or sandbox boundary.\nC:N - No data is disclosed: the hardening check aborts the transfer rather than permitting an out-of-bounds read, and the source region is legitimate, in-object packet payload the client requested. Removing the whitelist gap loosens the check, so the defect grants no read primitive.\nI:N - Nothing is written or corrupted \u2014 the code path ends in a defensive `usercopy_abort()` before any copy occurs, so there is no overwrite, type confusion, or control-flow hijack primitive.\nA:H - `usercopy_abort()` calls `BUG()`, producing a kernel oops in the `cifs_demultiplex_thread` kthread \u2014 a full panic under `panic_on_oops` (routinely paired with hardened-usercopy builds) and otherwise a dead demultiplex thread that permanently wedges the mount. The remote peer can trigger this repeatedly on every connection attempt."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:02:35.936Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/87dcc7e33fc3dcb8ed32333cec016528b5bb6ce4"
        },
        {
          "url": "https://git.kernel.org/stable/c/f0dd353d47f7051afa98c6c60c7486831eb1a410"
        },
        {
          "url": "https://git.kernel.org/stable/c/43e7e284fc77b710d899569360ea46fa3374ae22"
        }
      ],
      "title": "cifs: Fix the smbd_response slab to allow usercopy",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-38523",
    "datePublished": "2025-08-16T11:12:17.254Z",
    "dateReserved": "2025-04-16T04:51:24.023Z",
    "dateUpdated": "2026-08-05T12:02:35.936Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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