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GHSA-X7Q6-9X5C-R9X7

Vulnerability from github – Published: 2026-10-06 09:31 – Updated: 2026-10-06 09:31

Details

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

netlink: do not free nlk->groups while lockless readers can use it

netlink_realloc_groups() uses krealloc() under netlink_table_grab(). Whenever NLGRPSZ(groups) lands in a different kmalloc bucket, the old bitmap is freed immediately.

Two readers of nlk->groups / nlk->ngroups do not hold the netlink table lock:

1) sk_diag_dump_groups(). Hashed (bound) sockets are dumped from the rhashtable walk in __netlink_diag_dump(), which only holds RCU. Only the mc_list part of the dump takes nl_table_lock.

2) netlink_native_seq_show() (/proc/net/netlink), whose walk has been lockless since commit 21e4902aea80 ("netlink: Lockless lookup with RCU grace period in socket release").

Both can read a freed buffer, and sk_diag_dump_groups() can also read past the end of the old (smaller) buffer if it happens to load the old @groups pointer together with the new @ngroups value, copying the result into a NETLINK_DIAG_GROUPS attribute.

This is the same class of bug that commit f773608026ee ("netlink: access nlk groups safely in netlink bind and getname") fixed for bind() and getname(); these two readers were missed. Simply grabbing the table lock in sk_diag_dump_groups() is not an option, because it is also called with nl_table_lock already held from the mc_list section of the dump.

Make the lockless readers safe instead:

Allocate a new bitmap and free the old one after an RCU grace period, instead of relying on the implicit kfree() done by krealloc().
Publish @groups before @ngroups, both with release semantics, and have the lockless readers load @ngroups first. A reader can then never pair the new (bigger) size with the old (smaller) buffer, and a reader picking up the new pointer while still seeing the old size is guaranteed to see the initialized bitmap.

netlink_realloc_groups() is called from process context (bind() and setsockopt()), so kfree_rcu_mightsleep() can be used, once the table has been released.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98284"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-06T09:18:18Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetlink: do not free nlk-\u003egroups while lockless readers can use it\n\nnetlink_realloc_groups() uses krealloc() under netlink_table_grab().\nWhenever NLGRPSZ(groups) lands in a different kmalloc bucket, the old\nbitmap is freed immediately.\n\nTwo readers of nlk-\u003egroups / nlk-\u003engroups do not hold the netlink\ntable lock:\n\n1) sk_diag_dump_groups(). Hashed (bound) sockets are dumped from the\n   rhashtable walk in __netlink_diag_dump(), which only holds RCU.\n   Only the mc_list part of the dump takes nl_table_lock.\n\n2) netlink_native_seq_show() (/proc/net/netlink), whose walk has been\n   lockless since commit 21e4902aea80 (\"netlink: Lockless lookup with\n   RCU grace period in socket release\").\n\nBoth can read a freed buffer, and sk_diag_dump_groups() can also read\npast the end of the old (smaller) buffer if it happens to load the old\n@groups pointer together with the new @ngroups value, copying the\nresult into a NETLINK_DIAG_GROUPS attribute.\n\nThis is the same class of bug that commit f773608026ee (\"netlink:\naccess nlk groups safely in netlink bind and getname\") fixed for bind()\nand getname(); these two readers were missed. Simply grabbing the table\nlock in sk_diag_dump_groups() is not an option, because it is also\ncalled with nl_table_lock already held from the mc_list section of the\ndump.\n\nMake the lockless readers safe instead:\n\n- Allocate a new bitmap and free the old one after an RCU grace period,\n  instead of relying on the implicit kfree() done by krealloc().\n\n- Publish @groups before @ngroups, both with release semantics, and have\n  the lockless readers load @ngroups first. A reader can then never pair\n  the new (bigger) size with the old (smaller) buffer, and a reader\n  picking up the new pointer while still seeing the old size is\n  guaranteed to see the initialized bitmap.\n\nnetlink_realloc_groups() is called from process context (bind() and\nsetsockopt()), so kfree_rcu_mightsleep() can be used, once the table\nhas been released.",
  "id": "GHSA-x7q6-9x5c-r9x7",
  "modified": "2026-10-06T09:31:33Z",
  "published": "2026-10-06T09:31:33Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98284"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/22f313e211d58a66786c81487c3905fa5d4b2a8f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ceac0de741bfb47ca255eee075257b3bb31f0651"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-98284 (GCVE-0-2026-98284)

Vulnerability from cvelistv5 – Published: 2026-10-06 08:45 – Updated: 2026-10-06 08:45

Title

netlink: do not free nlk->groups while lockless readers can use it

Summary

In the Linux kernel, the following vulnerability has been resolved: netlink: do not free nlk->groups while lockless readers can use it netlink_realloc_groups() uses krealloc() under netlink_table_grab(). Whenever NLGRPSZ(groups) lands in a different kmalloc bucket, the old bitmap is freed immediately. Two readers of nlk->groups / nlk->ngroups do not hold the netlink table lock: 1) sk_diag_dump_groups(). Hashed (bound) sockets are dumped from the rhashtable walk in __netlink_diag_dump(), which only holds RCU. Only the mc_list part of the dump takes nl_table_lock. 2) netlink_native_seq_show() (/proc/net/netlink), whose walk has been lockless since commit 21e4902aea80 ("netlink: Lockless lookup with RCU grace period in socket release"). Both can read a freed buffer, and sk_diag_dump_groups() can also read past the end of the old (smaller) buffer if it happens to load the old @groups pointer together with the new @ngroups value, copying the result into a NETLINK_DIAG_GROUPS attribute. This is the same class of bug that commit f773608026ee ("netlink: access nlk groups safely in netlink bind and getname") fixed for bind() and getname(); these two readers were missed. Simply grabbing the table lock in sk_diag_dump_groups() is not an option, because it is also called with nl_table_lock already held from the mc_list section of the dump. Make the lockless readers safe instead: - Allocate a new bitmap and free the old one after an RCU grace period, instead of relying on the implicit kfree() done by krealloc(). - Publish @groups before @ngroups, both with release semantics, and have the lockless readers load @ngroups first. A reader can then never pair the new (bigger) size with the old (smaller) buffer, and a reader picking up the new pointer while still seeing the old size is guaranteed to see the initialized bitmap. netlink_realloc_groups() is called from process context (bind() and setsockopt()), so kfree_rcu_mightsleep() can be used, once the table has been released.

Severity

No CVSS data available.

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 6664 records in the last 180 days details

References

2 references

URL	Tags
https://git.kernel.org/stable/c/22f313e211d58a667…
https://git.kernel.org/stable/c/ceac0de741bfb47ca…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 21e4902aea80ef35afc00ee8d2abdea4f519b7f7 , < 22f313e211d58a66786c81487c3905fa5d4b2a8f (git) Affected: 21e4902aea80ef35afc00ee8d2abdea4f519b7f7 , < ceac0de741bfb47ca255eee075257b3bb31f0651 (git)
Linux	Linux	Affected: 4.0 Unaffected: 0 , < 4.0 (semver) Unaffected: 7.2.8 , ≤ 7.2.* (semver) Unaffected: 7.3-rc4 , ≤ * (original_commit_for_fix)

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        {
          "defaultStatus": "unaffected",
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          "programFiles": [
            "net/netlink/af_netlink.c",
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          ],
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          "versions": [
            {
              "lessThan": "22f313e211d58a66786c81487c3905fa5d4b2a8f",
              "status": "affected",
              "version": "21e4902aea80ef35afc00ee8d2abdea4f519b7f7",
              "versionType": "git"
            },
            {
              "lessThan": "ceac0de741bfb47ca255eee075257b3bb31f0651",
              "status": "affected",
              "version": "21e4902aea80ef35afc00ee8d2abdea4f519b7f7",
              "versionType": "git"
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          ],
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            {
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              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
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              "version": "7.2.8",
              "versionType": "semver"
            },
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              "status": "unaffected",
              "version": "7.3-rc4",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
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            {
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetlink: do not free nlk-\u003egroups while lockless readers can use it\n\nnetlink_realloc_groups() uses krealloc() under netlink_table_grab().\nWhenever NLGRPSZ(groups) lands in a different kmalloc bucket, the old\nbitmap is freed immediately.\n\nTwo readers of nlk-\u003egroups / nlk-\u003engroups do not hold the netlink\ntable lock:\n\n1) sk_diag_dump_groups(). Hashed (bound) sockets are dumped from the\n   rhashtable walk in __netlink_diag_dump(), which only holds RCU.\n   Only the mc_list part of the dump takes nl_table_lock.\n\n2) netlink_native_seq_show() (/proc/net/netlink), whose walk has been\n   lockless since commit 21e4902aea80 (\"netlink: Lockless lookup with\n   RCU grace period in socket release\").\n\nBoth can read a freed buffer, and sk_diag_dump_groups() can also read\npast the end of the old (smaller) buffer if it happens to load the old\n@groups pointer together with the new @ngroups value, copying the\nresult into a NETLINK_DIAG_GROUPS attribute.\n\nThis is the same class of bug that commit f773608026ee (\"netlink:\naccess nlk groups safely in netlink bind and getname\") fixed for bind()\nand getname(); these two readers were missed. Simply grabbing the table\nlock in sk_diag_dump_groups() is not an option, because it is also\ncalled with nl_table_lock already held from the mc_list section of the\ndump.\n\nMake the lockless readers safe instead:\n\n- Allocate a new bitmap and free the old one after an RCU grace period,\n  instead of relying on the implicit kfree() done by krealloc().\n\n- Publish @groups before @ngroups, both with release semantics, and have\n  the lockless readers load @ngroups first. A reader can then never pair\n  the new (bigger) size with the old (smaller) buffer, and a reader\n  picking up the new pointer while still seeing the old size is\n  guaranteed to see the initialized bitmap.\n\nnetlink_realloc_groups() is called from process context (bind() and\nsetsockopt()), so kfree_rcu_mightsleep() can be used, once the table\nhas been released."
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    "datePublished": "2026-10-06T08:45:45.443Z",
    "dateReserved": "2026-09-25T10:25:14.335Z",
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}

Sightings

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Nomenclature

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Confirmed: The vulnerability has been validated from an analyst's perspective.
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Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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