From 732e3e10234cbe302d0dcbaa98c91c66628209cb Mon Sep 17 00:00:00 2001 From: Karl Mehltretter Date: Thu, 27 Aug 2026 06:17:08 +0200 Subject: [PATCH] klist: avoid accesses after waking klist_remove() klist_remove() waits until a node is unreferenced so that its caller can free the containing object. klist_release() currently publishes waiter->woken and wakes the waiter before its final accesses to the waiter and node. klist_remove() can then return, allowing its stack waiter and the containing object to be freed or reused while klist_release() is still running. In particular, bus_remove_driver() can free drv->p while __device_attach() walks the same bus klist with bus_for_each_drv(). On an arm64 Cortex-A72 system, an unpatched 7.2.0-rc3 kernel with CONFIG_PREEMPT_RT=y and CONFIG_KASAN=y reproduced the bug through the in-tree I2C/at24 path. KASAN reported a use-after-free in klist_dec_and_del() reached from klist_next()/bus_for_each_drv() while at24 was being unregistered. Clear n_klist and take a task reference before publishing woken. Use release/acquire accesses for that publication and wake the referenced task. The task reference keeps the waiter task alive if it returns and exits before wake_up_process(). Link: https://lore.kernel.org/20260827041708.31682-1-kmehltretter@gmail.com Fixes: 8b0c250be489 ("[PATCH] add klist_node_attached() to determine if a node is on a list or not.") Fixes: 210272a28465 ("driver core: Remove completion from struct klist_node") Signed-off-by: Karl Mehltretter Signed-off-by: Andrew Morton Assisted-by: LLM Cc: Danilo Krummrich Cc: Greg Kroah-Hartman Cc: Matthew Wilcox (Oracle) Cc: "Rafael J. Wysocki" Cc: --- lib/klist.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/lib/klist.c b/lib/klist.c index 332a4fbf18ff..f133740b1c2c 100644 --- a/lib/klist.c +++ b/lib/klist.c @@ -36,6 +36,7 @@ #include #include #include +#include /* * Use the lowest bit of n_klist to mark deleted nodes and exclude @@ -187,18 +188,24 @@ static void klist_release(struct kref *kref) WARN_ON(!knode_dead(n)); list_del(&n->n_node); + knode_set_klist(n, NULL); spin_lock(&klist_remove_lock); list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) { + struct task_struct *p; + if (waiter->node != n) continue; + p = waiter->process; + get_task_struct(p); list_del(&waiter->list); - waiter->woken = 1; + /* Publish only after the final waiter and n accesses */ + smp_store_release(&waiter->woken, 1); mb(); - wake_up_process(waiter->process); + wake_up_process(p); + put_task_struct(p); } spin_unlock(&klist_remove_lock); - knode_set_klist(n, NULL); } static int klist_dec_and_del(struct klist_node *n) @@ -250,7 +257,8 @@ void klist_remove(struct klist_node *n) for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); - if (waiter.woken) + /* Pairs with the release store in klist_release() */ + if (smp_load_acquire(&waiter.woken)) break; schedule(); }