sched_ext: Close the pre-enable ops error claim window

Summary

In the Linux kernel, the following vulnerability has been resolved: sched_ext: Close the pre-enable ops error claim window scx_alloc_and_add_sched() publishes ops->priv before scx_root_enable_workfn() switches the state to SCX_ENABLING. An error claimed via scx_bpf_error_bstr() from an associated BPF program in that window is consumed by scx_disable_workfn(), which takes the pre-enable shortcut in scx_root_disable(). The shortcut returns without any teardown and restores SCX_DISABLED with an unconditional scx_set_enable_state() xchg racing the enable workfn's own transition. The enable then completes with the claim consumed: the scheduler stays up but can never be disabled again, and bpf_scx_unreg() frees it while still in use, resulting in a use-after-free. Both WARN_ON_ONCE()s fire back to back: WARNING: kernel/sched/ext/ext.c:7522 at scx_root_enable_workfn+0xeec/0x1be0, CPU#3: scx_enable_help/276 WARNING: kernel/sched/ext/ext.c:6398 at scx_root_disable+0xb50/0xdb8, CPU#0: sched_ext_helpe/664 scx_root_enable_workfn() switches to SCX_ENABLING before the scheduler allocation, so ops->priv is never visible while SCX_DISABLED. The allocation failure path restores SCX_DISABLED.

Timeline

1. Oct 6, 2026, 8:44 AM UTCCVE published
2. Oct 19, 2026, 9:15 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 105dcd005be2ac1d5541921db8feb1d0f98d59d5 · fixed in 959c66dc4a915be306c35691095c787c61dc7df9; From 105dcd005be2ac1d5541921db8feb1d0f98d59d5 · fixed in c7a1c6e8004ab12a9c9bfdcb603f60f9bf4a3cee

• Linux Linux

  7.1

• KernelLinux

  From 7.1.0 · fixed in 7.2.8

References 2