From: Qian Cai <cai@lca.pw>
To: peterz@infradead.org, mingo@redhat.com
Cc: will@kernel.org, dbueso@suse.de, juri.lelli@redhat.com,
longman@redhat.com, linux-kernel@vger.kernel.org,
Qian Cai <cai@lca.pw>
Subject: [PATCH -next v2] locking/percpu-rwsem: fix a task_struct refcount
Date: Mon, 30 Mar 2020 17:30:02 -0400 [thread overview]
Message-ID: <20200330213002.2374-1-cai@lca.pw> (raw)
The commit 7f26482a872c ("locking/percpu-rwsem: Remove the embedded
rwsem") introduced some task_struct memory leaks due to messing up with
a 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 <peterz@infradead.org>
Signed-off-by: Qian Cai <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);
--
2.21.0 (Apple Git-122.2)
next reply other threads:[~2020-03-30 21:30 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-30 21:30 Qian Cai [this message]
2020-04-06 13:31 ` [PATCH -next v2] locking/percpu-rwsem: fix a task_struct refcount Qian Cai
2020-04-06 14:09 ` Peter Zijlstra
2020-04-08 12:20 ` [tip: locking/urgent] locking/percpu-rwsem: Fix " tip-bot2 for Qian Cai
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