CVE-2026-90248 — net/sched: cls_api: fix teardown of an adopted proto on insert-race loss

Affected: Linux

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

net/sched: cls_api: fix teardown of an adopted proto on insert-race loss

In tc_new_tfilter() the create branch sets tp_created = 1 before calling tcf_chain_tp_insert_unique(). When the caller loses the race (another request inserted a proto at the same chain/prio first), insert_unique() destroys the caller's own tp_new and returns the winner's proto with an extra reference. tp_created was never cleared, so the loser's errout path treated the winner's live proto as its own and called tcf_chain_tp_delete_empty() on it, silently unlinking an active classifier that the winning request already advertised via RTM_NEWTFILTER.

Track the outcome of the insert step in a single tri-state variable so each errout path reacts correctly:

- TP_NOT_CREATED: no proto created; pursue the old path. - TP_CREATED: proto inserted successfully; same code path as before. - TP_NOT_OWNED: New - lost the insert race; tp is another request's proto (chain ref already released by tp_new's destroy)

Both errout reactions are single expressions derived from the state.

This fix is motivated by the Sashiko's automated review of Patch (net/sched: cls_api: Always acquire rtnl_lock when destroying locked classifiers) [1][2]. The review identified the silent-unlink behaviour of an adopted proto's teardown when a request loses the tcf_chain_tp_insert_unique() race.

[1] https://sashiko.dev/#/patchset/20260801125632.360365-1-jhs%40mojatatu.c…

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CVE-2026-90248 — net/sched: cls_api: fix teardown of an adopted proto on insert-race loss