CVE-2026-98220
Vulnérabilité non évaluée dans Linux (Linux)
Description
In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix NULL sched deref in kfunc sub-sched error paths When the root scheduler has sub-scheds attached, the COMPAT kfunc wrappers scx_bpf_select_cpu_and() and scx_bpf_dsq_insert_vtime() refuse the call and report to @p's scheduler: scx_error(scx_task_sched(p), "... must be used"); The wrappers are reachable with tasks that have no scheduler. scx_bpf_select_cpu_and() is in the select_cpu kfunc group, which scx_kfunc_context_filter() opens to BPF_PROG_TYPE_SYSCALL programs; scx_bpf_dsq_insert_vtime() is in the enqueue_dispatch group, which ops.enqueue() and ops.dispatch() may call with any KF_RCU task -- the group has no kf_tasks validation, and scx_dsq_insert_preamble() checks task ownership with scx_task_on_sched() precisely because @p may be an arbitrary task. scx_task_sched(p) is p->scx.sched, which is NULL for tasks past sched_ext_dead() -- which clears it via scx_disable_and_exit_task() on exit -- and for idle tasks, which the enable paths skip as they are never scheduled through SCX. It is also an rcu_dereference_protected() that expects @p's pi_lock or rq lock, which neither wrapper holds. Passing NULL to scx_error() reaches scx_vexit(), which dereferences sch->exit_info, oopsing the kernel. One concrete trigger exercised while developing the fix: a BPF_PROG_TYPE_SYSCALL program calling the select_cpu_and wrapper on an exited-but-not-reaped task while a sub-scheduler was attached (its pid stays findable while the zombie is unreaped; faulting instruction is the scx_vexit() prologue "mov r15,[rdi+0x398]" with RDI=NULL and 0x398 the offset of sch->exit_info): sched_ext: BPF scheduler "kfunc_subsched_null" enabled sched_ext: BPF sub-scheduler "kfunc_subsched_null" enabled sched_ext: Unassociated program run_select_cpu_ (id 76) BUG: kernel NULL pointer dereference, address: 0000000000000398 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page Oops: Oops: 0000 [#1] SMP NOPTI CPU: 7 UID: 0 PID: 8201 Comm: kfunc_test_runn Tainted: G W RIP: 0010:scx_vexit+0x25/0xa0 Code: ... <4c> 8b bf 98 03 00 00 ... CR2: 0000000000000398 Call Trace: <TASK> __scx_exit+0x4f/0x70 scx_bpf_select_cpu_and+0xab/0xb0 bpf_prog_430ed61a7b66e03a_run_select_cpu_and+0x9c/0xe7 ? __x64_sys_bpf+0x2c/0x40 bpf_prog_test_run_syscall+0x130/0x2f0 __sys_bpf+0x930/0x10d0 ? __x64_sys_bpf+0x2c/0x40 __x64_sys_bpf+0x2c/0x40 do_syscall_64+0xbc/0x460 entry_SYSCALL_64_after_hwframe+0x76/0x7e </TASK> Read @p's scheduler under RCU instead, which the wrappers can do from their guard(rcu)(): fault it when it can be determined, and when it can't be determined -- @p is a task past sched_ext_dead() or an idle task -- there is nothing obviously wrong to report, so just refuse the call as before without faulting any scheduler. These COMPAT wrappers are scheduled for eventual removal once the deprecation grace period elapses, but until then -- and regardless of their removal timeline -- they must not oops the kernel on a task they are handed.
Gravité et risque d'exploitation
CVE-2026-98220 obtient un score CVSS de 0.0/10, soit une gravité non évaluée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.20 %, ce qui la place devant 8.9 % des CVE référencées.
Que faire ?
- Vérifiez si Linux (versions <7.1, <=*, 7.2.8, a5fa0708cbfda4d3c2c6a447de7c4b0b23595527, 7.1, <0a85182723b65ad8bee8131bc38fcf0347d6679b, 0, <=7.2.*, <589f0945bf3ebf0790fd51e28c7f0d04ed3d8b78, 7.3) est présent sur votre parc.
- Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
- À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
- Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.