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[2a02:3100:af54:b201:7419:a557:62e9:4d13]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6a59e00108asm17474345a12.2.2026.08.24.21.04.16 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 24 Aug 2026 21:04:17 -0700 (PDT) From: Karl Mehltretter To: Andrew Morton Cc: Karl Mehltretter , Matthew Wilcox , Greg Kroah-Hartman , "Rafael J. Wysocki" , Danilo Krummrich , driver-core@lists.linux.dev, linux-kernel@vger.kernel.org, syzbot+9cb1ac7fce4944ba9165@syzkaller.appspotmail.com, stable@vger.kernel.org Subject: [PATCH] klist: avoid accesses after waking klist_remove() Date: Tue, 25 Aug 2026 06:04:08 +0200 Message-Id: <20260825040408.59225-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: driver-core@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit klist_release() publishes waiter->woken before its final accesses to the stack waiter and node. klist_remove() can then return, allowing the waiter to go out of scope and its caller to free or reuse the node. 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(). wake_up_process() provides the full barrier required by the sleep/wakeup protocol, so remove the explicit mb(). 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") Reported-by: syzbot+9cb1ac7fce4944ba9165@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9cb1ac7fce4944ba9165 Tested-by: syzbot+9cb1ac7fce4944ba9165@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Karl Mehltretter --- lib/klist.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/lib/klist.c b/lib/klist.c index 332a4fbf18ff..7242f4cc1c1b 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 +188,23 @@ 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; - mb(); - wake_up_process(waiter->process); + /* Publish only after the final waiter and n accesses */ + smp_store_release(&waiter->woken, 1); + 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 +256,8 @@ 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(); } -- 2.39.5 (Apple Git-154)