From: Jiayuan Chen Date: Mon, 30 Mar 2026 07:32:29 +0000 (+0800) Subject: irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT X-Git-Tag: v7.1-rc4~7^2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=91840be8f710370607f949a627e070896faeddb8;p=thirdparty%2Fkernel%2Flinux.git irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT On PREEMPT_RT, non-HARD irq_work runs in per-CPU kthreads via run_irq_workd(), so irq_work_sync() uses rcuwait() to wait for BUSY==0. After irq_work_single() clears BUSY via atomic_cmpxchg(), it still dereferences @work for irq_work_is_hard() and rcuwait_wake_up(). An irq_work_sync() caller on another CPU that enters after BUSY is cleared can observe BUSY==0 immediately, return, and free the work before those accesses complete — causing a use-after-free. Fix this by wrapping run_irq_workd() in guard(rcu)() so that the entire irq_work_single() execution is within an RCU read-side critical section. Then add synchronize_rcu() in irq_work_sync() after rcuwait_wait_event() to ensure the caller waits for the RCU grace period before returning, preventing premature frees. Fixes: 810979682ccc ("irq_work: Allow irq_work_sync() to sleep if irq_work() no IRQ support.") Suggested-by: Sebastian Andrzej Siewior Suggested-by: Steven Rostedt Signed-off-by: Jiayuan Chen Signed-off-by: Thomas Gleixner Reviewed-by: Sebastian Andrzej Siewior Link: https://patch.msgid.link/20260330073234.303732-1-jiayuan.chen@linux.dev --- diff --git a/kernel/irq_work.c b/kernel/irq_work.c index 120fd7365fbe..f7e2dc2c30c6 100644 --- a/kernel/irq_work.c +++ b/kernel/irq_work.c @@ -292,6 +292,12 @@ void irq_work_sync(struct irq_work *work) !arch_irq_work_has_interrupt()) { rcuwait_wait_event(&work->irqwait, !irq_work_is_busy(work), TASK_UNINTERRUPTIBLE); + /* + * Ensure irq_work_single() does not access @work + * after removing IRQ_WORK_BUSY. It is always + * accessed within a RCU-read section. + */ + synchronize_rcu(); return; } @@ -302,6 +308,7 @@ EXPORT_SYMBOL_GPL(irq_work_sync); static void run_irq_workd(unsigned int cpu) { + guard(rcu)(); irq_work_run_list(this_cpu_ptr(&lazy_list)); }