GHSA-6RJ2-XG9P-3JJ4

Vulnerability from github – Published: 2026-03-25 12:30 – Updated: 2026-05-29 18:31
VLAI
Details

In the Linux kernel, the following vulnerability has been resolved:

atm: lec: fix null-ptr-deref in lec_arp_clear_vccs

syzkaller reported a null-ptr-deref in lec_arp_clear_vccs(). This issue can be easily reproduced using the syzkaller reproducer.

In the ATM LANE (LAN Emulation) module, the same atm_vcc can be shared by multiple lec_arp_table entries (e.g., via entry->vcc or entry->recv_vcc). When the underlying VCC is closed, lec_vcc_close() iterates over all ARP entries and calls lec_arp_clear_vccs() for each matched entry.

For example, when lec_vcc_close() iterates through the hlists in priv->lec_arp_empty_ones or other ARP tables:

  1. In the first iteration, for the first matched ARP entry sharing the VCC, lec_arp_clear_vccs() frees the associated vpriv (which is vcc->user_back) and sets vcc->user_back to NULL.
  2. In the second iteration, for the next matched ARP entry sharing the same VCC, lec_arp_clear_vccs() is called again. It obtains a NULL vpriv from vcc->user_back (via LEC_VCC_PRIV(vcc)) and then attempts to dereference it via vcc->pop = vpriv->old_pop, leading to a null-ptr-deref crash.

Fix this by adding a null check for vpriv before dereferencing it. If vpriv is already NULL, it means the VCC has been cleared by a previous call, so we can safely skip the cleanup and just clear the entry's vcc/recv_vcc pointers.

The entire cleanup block (including vcc_release_async()) is placed inside the vpriv guard because a NULL vpriv indicates the VCC has already been fully released by a prior iteration — repeating the teardown would redundantly set flags and trigger callbacks on an already-closing socket.

The Fixes tag points to the initial commit because the entry->vcc path has been vulnerable since the original code. The entry->recv_vcc path was later added by commit 8d9f73c0ad2f ("atm: fix a memory leak of vcc->user_back") with the same pattern, and both paths are fixed here.

Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-23286"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-476"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-03-25T11:16:23Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\natm: lec: fix null-ptr-deref in lec_arp_clear_vccs\n\nsyzkaller reported a null-ptr-deref in lec_arp_clear_vccs().\nThis issue can be easily reproduced using the syzkaller reproducer.\n\nIn the ATM LANE (LAN Emulation) module, the same atm_vcc can be shared by\nmultiple lec_arp_table entries (e.g., via entry-\u003evcc or entry-\u003erecv_vcc).\nWhen the underlying VCC is closed, lec_vcc_close() iterates over all\nARP entries and calls lec_arp_clear_vccs() for each matched entry.\n\nFor example, when lec_vcc_close() iterates through the hlists in\npriv-\u003elec_arp_empty_ones or other ARP tables:\n\n1. In the first iteration, for the first matched ARP entry sharing the VCC,\nlec_arp_clear_vccs() frees the associated vpriv (which is vcc-\u003euser_back)\nand sets vcc-\u003euser_back to NULL.\n2. In the second iteration, for the next matched ARP entry sharing the same\nVCC, lec_arp_clear_vccs() is called again. It obtains a NULL vpriv from\nvcc-\u003euser_back (via LEC_VCC_PRIV(vcc)) and then attempts to dereference it\nvia `vcc-\u003epop = vpriv-\u003eold_pop`, leading to a null-ptr-deref crash.\n\nFix this by adding a null check for vpriv before dereferencing\nit. If vpriv is already NULL, it means the VCC has been cleared\nby a previous call, so we can safely skip the cleanup and just\nclear the entry\u0027s vcc/recv_vcc pointers.\n\nThe entire cleanup block (including vcc_release_async()) is placed inside\nthe vpriv guard because a NULL vpriv indicates the VCC has already been\nfully released by a prior iteration \u2014 repeating the teardown would\nredundantly set flags and trigger callbacks on an already-closing socket.\n\nThe Fixes tag points to the initial commit because the entry-\u003evcc path has\nbeen vulnerable since the original code. The entry-\u003erecv_vcc path was later\nadded by commit 8d9f73c0ad2f (\"atm: fix a memory leak of vcc-\u003euser_back\")\nwith the same pattern, and both paths are fixed here.",
  "id": "GHSA-6rj2-xg9p-3jj4",
  "modified": "2026-05-29T18:31:13Z",
  "published": "2026-03-25T12:30:21Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23286"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/101bacb303e89dc2e0640ae6a5e0fb97c4eb45bb"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2d9f57ea29a1f1772373b98a509b44d49fda609e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/30c9744a989feb22cfbb84170eb0e038a7a2c1da"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5f1cfea7921f5c126a441d973690eeba52677b64"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/622062f24644b4536d3f437e0cf7a8c4bb421665"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7ea92ab075d809ec8a96669a5ecf00f752057875"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8aff65a82b6389ec674d46e5b3d3ae6f07db5e3e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e9665986eb127290ceb535bd5d04d7a84265d94f"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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