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CVE-2025-38721

Full vulnerability record from the local CVENow database.

Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: fix refcount leak on table dump There is a reference count leak in ctnetlink_dump_table(): if (res < 0) { nf_conntrack_get(&ct->ct_general); // HERE cb->args[1] = (unsigned long)ct; ... While its very unlikely, its possible that ct == last. If this happens, then the refcount of ct was already incremented. This 2nd increment is never undone. This prevents the conntrack object from being released, which in turn keeps prevents cnet->count from dropping back to 0. This will then block the netns dismantle (or conntrack rmmod) as nf_conntrack_cleanup_net_list() will wait forever. This can be reproduced by running conntrack_resize.sh selftest in a loop. It takes ~20 minutes for me on a preemptible kernel on average before I see a runaway kworker spinning in nf_conntrack_cleanup_net_list. One fix would to change this to: if (res < 0) { if (ct != last) nf_conntrack_get(&ct->ct_general); But this reference counting isn't needed in the first place. We can just store a cookie value instead. A followup patch will do the same for ctnetlink_exp_dump_table, it looks to me as if this has the same problem and like ctnetlink_dump_table, we only need a 'skip hint', not the actual object so we can apply the same cookie strategy there as well.

Severity
MEDIUM
CVSS score
5.5 (v3.1)
Vulnerability status
Modified
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2025-09-04 16:15:41.843000
Last modified
2026-10-19 21:10:00.160000
View original CVE JSON 
{
  "id": "CVE-2025-38721",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2025-09-04T16:15:41.843",
  "lastModified": "2026-10-19T21:10:00.160",
  "vulnStatus": "Modified",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: ctnetlink: fix refcount leak on table dump\n\nThere is a reference count leak in ctnetlink_dump_table():\n      if (res < 0) {\n                nf_conntrack_get(&ct->ct_general); // HERE\n                cb->args[1] = (unsigned long)ct;\n                ...\n\nWhile its very unlikely, its possible that ct == last.\nIf this happens, then the refcount of ct was already incremented.\nThis 2nd increment is never undone.\n\nThis prevents the conntrack object from being released, which in turn\nkeeps prevents cnet->count from dropping back to 0.\n\nThis will then block the netns dismantle (or conntrack rmmod) as\nnf_conntrack_cleanup_net_list() will wait forever.\n\nThis can be reproduced by running conntrack_resize.sh selftest in a loop.\nIt takes ~20 minutes for me on a preemptible kernel on average before\nI see a runaway kworker spinning in nf_conntrack_cleanup_net_list.\n\nOne fix would to change this to:\n        if (res < 0) {\n\t\tif (ct != last)\n\t                nf_conntrack_get(&ct->ct_general);\n\nBut this reference counting isn't needed in the first place.\nWe can just store a cookie value instead.\n\nA followup patch will do the same for ctnetlink_exp_dump_table,\nit looks to me as if this has the same problem and like\nctnetlink_dump_table, we only need a 'skip hint', not the actual\nobject so we can apply the same cookie strategy there as well."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nnetfilter: ctnetlink: corrección de fuga de contador de referencias en el volcado de tabla\n\nHay una fuga de contador de referencias en ctnetlink_dump_table():\n      if (res < 0) {\n                nf_conntrack_get(&ct->ct_general); // AQUÍ\n                cb->args[1] = (unsigned long)ct;\n                ...\n\nAunque es muy improbable, es posible que ct == last.\nSi esto ocurre, entonces el contador de referencias de ct ya se había incrementado.\nEste segundo incremento nunca se deshace.\n\nEsto evita que el objeto conntrack sea liberado, lo que a su vez\nimpide que cnet->count vuelva a 0.\n\nEsto entonces bloqueará el desmantelamiento de netns (o rmmod de conntrack) ya que\nnf_conntrack_cleanup_net_list() esperará indefinidamente.\n\nEsto puede reproducirse ejecutando la autoprueba conntrack_resize.sh en un bucle.\nMe lleva ~20 minutos en un kernel preemptivo en promedio antes de que\nvea un kworker descontrolado girando en nf_conntrack_cleanup_net_list.\n\nUna solución sería cambiar esto a:\n        if (res < 0) {\n\t\tif (ct != last)\n\t                nf_conntrack_get(&ct->ct_general);\n\nPero este conteo de referencias no es necesario en primer lugar.\nPodemos simplemente almacenar un valor de cookie en su lugar.\n\nUn parche de seguimiento hará lo mismo para ctnetlink_exp_dump_table,\nme parece que esto tiene el mismo problema y al igual que\nctnetlink_dump_table, solo necesitamos una 'pista de salto', no el objeto real,\nasí que podemos aplicar la misma estrategia de cookie allí también."
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