From: Amery Hung Date: Thu, 19 Mar 2026 02:57:16 +0000 (-0700) Subject: bpf: Do not allow deleting local storage in NMI X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=350de5b8a9befaa2a68861c51f671d4f5f751ca5;p=thirdparty%2Flinux.git bpf: Do not allow deleting local storage in NMI Currently, local storage may deadlock when deferring freeing selem or local storage through kfree_rcu(), call_rcu() or call_rcu_tasks_trace() in NMI or reentrant. Since deleting selem in NMI is an unlikely use case, partially mitigate it by returning error when calling from bpf_xxx_storage_delete() helpers in NMI. Note that, it is still possible to deadlock through reentrant. A full mitigation requires returning error when irqs_disabled() is true, which, however is too heavy-handed for bpf_xxx_storage_delete(). The long-term solution requires _nolock versions of call_rcu. Another possible solution is to defer the free through irq_work [0], but it would grow the size of selem, which is non-ideal. The check is only needed in bpf_selem_unlink(), which is used by helpers and syscalls. bpf_selem_unlink_nofail() is fine as it is called during map and owner tear down that never run in NMI or reentrant. [0] https://lore.kernel.org/bpf/20260205190233.912-1-alexei.starovoitov@gmail.com/ Fixes: a10787e6d58c ("bpf: Enable task local storage for tracing programs") Signed-off-by: Amery Hung Signed-off-by: Martin KaFai Lau Acked-by: Kumar Kartikeya Dwivedi Link: https://patch.msgid.link/20260319025716.2361065-1-ameryhung@gmail.com --- diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c index 9c96a4477f81a..4c6079d2cf28d 100644 --- a/kernel/bpf/bpf_local_storage.c +++ b/kernel/bpf/bpf_local_storage.c @@ -393,6 +393,9 @@ int bpf_selem_unlink(struct bpf_local_storage_elem *selem) unsigned long flags; int err; + if (in_nmi()) + return -EOPNOTSUPP; + if (unlikely(!selem_linked_to_storage_lockless(selem))) /* selem has already been unlinked from sk */ return 0;