netfilter: ctnetlink: fix refcount leak on table dump

Summary

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.

Timeline

1. Sep 4, 2025, 3:33 PM UTCCVE published
2. Oct 15, 2026, 1:07 AM UTCRecord last updated

Affected versions

• Linux Linux

  From d205dc40798d97d63ad348bfaf7394f445d152d4 · fixed in 586892e341fbf698e7cbaca293e1353957db725a; From d205dc40798d97d63ad348bfaf7394f445d152d4 · fixed in 962518c6ca9f9a13df099cafa429f72f68ad61f0; From d205dc40798d97d63ad348bfaf7394f445d152d4 · fixed in 19b909a4b1452fb97e477d2f08b97f8d04095619; From d205dc40798d97d63ad348bfaf7394f445d152d4 · fixed in 41462f4cfc583513833f87f9ee55d12da651a7e3; From d205dc40798d97d63ad348bfaf7394f445d152d4 · fixed in 30cf811058552b8cd0e98dff677ef3f89d6d34ce; From d205dc40798d97d63ad348bfaf7394f445d152d4 · fixed in a2cb4df7872de069f809de2f076ec8e54d649fe3; From d205dc40798d97d63ad348bfaf7394f445d152d4 · fixed in e14f72aa66c029db106921d621edcedef68e065b; From d205dc40798d97d63ad348bfaf7394f445d152d4 · fixed in a62d6aa3f31f216b637a4c71b7a8bfc7c57f049b; From d205dc40798d97d63ad348bfaf7394f445d152d4 · fixed in de788b2e6227462b6dcd0e07474e72c089008f74

• Linux Linux

  2.6.18

• KernelLinux

  From 2.6.18 · fixed in 5.4.297; From 5.5.0 · fixed in 5.10.241; From 5.11.0 · fixed in 5.15.190; From 5.16.0 · fixed in 6.1.149; From 6.2.0 · fixed in 6.6.103; From 6.7.0 · fixed in 6.12.43; From 6.13.0 · fixed in 6.15.11; From 6.16.0 · fixed in 6.16.2

References 9