From d22cc7f67d55ebf2d5be865453971c783e9fb21a Mon Sep 17 00:00:00 2001 From: Qian Cai Date: Mon, 30 Mar 2020 17:30:02 -0400 Subject: locking/percpu-rwsem: Fix a task_struct refcount The following commit: 7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem") introduced task_struct memory leaks due to messing up the task_struct refcount. At the beginning of percpu_rwsem_wake_function(), it calls get_task_struct(), but if the trylock failed, it will remain in the waitqueue. However, it will run percpu_rwsem_wake_function() again with get_task_struct() to increase the refcount but then only call put_task_struct() once the trylock succeeded. Fix it by adjusting percpu_rwsem_wake_function() a bit to guard against when percpu_rwsem_wait() observing !private, terminating the wait and doing a quick exit() while percpu_rwsem_wake_function() then doing wake_up_process(p) as a use-after-free. Fixes: 7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem") Suggested-by: Peter Zijlstra Signed-off-by: Qian Cai Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lkml.kernel.org/r/20200330213002.2374-1-cai@lca.pw --- kernel/locking/percpu-rwsem.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c index a008a1ba21a7..8bbafe3e5203 100644 --- a/kernel/locking/percpu-rwsem.c +++ b/kernel/locking/percpu-rwsem.c @@ -118,14 +118,15 @@ static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode, int wake_flags, void *key) { - struct task_struct *p = get_task_struct(wq_entry->private); bool reader = wq_entry->flags & WQ_FLAG_CUSTOM; struct percpu_rw_semaphore *sem = key; + struct task_struct *p; /* concurrent against percpu_down_write(), can get stolen */ if (!__percpu_rwsem_trylock(sem, reader)) return 1; + p = get_task_struct(wq_entry->private); list_del_init(&wq_entry->entry); smp_store_release(&wq_entry->private, NULL); -- cgit