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Message-ID: <5bf6c167.1ed9.17f8b244e74.Coremail.duoming@zju.edu.cn>
Date: Tue, 15 Mar 2022 09:14:46 +0800 (GMT+08:00)
From: 周多明 <duoming@....edu.cn>
To: "Dan Carpenter" <dan.carpenter@...cle.com>
Cc: linux-hams@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, jreuter@...na.de, kuba@...nel.org,
davem@...emloft.net, ralf@...ux-mips.org, thomas@...erried.de
Subject: Re: Re: Re: [PATCH V3] ax25: Fix refcount leaks caused by
ax25_cb_del()
Hello,
On Mon, 14 Mar 2022 14:02:56 +0300, Dan Carpen wrote:
> > > But even here, my instinct is that if the refcounting is were done in
> > > the correct place we would not need any additional variables. Is there
> > > no simpler solution?
I think there is a simpler solution instead of using any additional variables,
which is shown below:
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 6bd09718077..0886109421a 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -98,8 +98,10 @@ static void ax25_kill_by_device(struct net_device *dev)
spin_unlock_bh(&ax25_list_lock);
lock_sock(sk);
s->ax25_dev = NULL;
- dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
- ax25_dev_put(ax25_dev);
+ if (sk->sk_wq) {
+ dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
+ ax25_dev_put(ax25_dev);
+ }
ax25_disconnect(s, ENETUNREACH);
release_sock(sk);
spin_lock_bh(&ax25_list_lock);
@@ -979,14 +981,20 @@ static int ax25_release(struct socket *sock)
{
struct sock *sk = sock->sk;
ax25_cb *ax25;
+ ax25_dev *ax25_dev;
if (sk == NULL)
return 0;
sock_hold(sk);
- sock_orphan(sk);
lock_sock(sk);
+ sock_orphan(sk);
ax25 = sk_to_ax25(sk);
+ ax25_dev = ax25->ax25_dev;
+ if (ax25_dev) {
+ dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
+ ax25_dev_put(ax25_dev);
+ }
if (sk->sk_type == SOCK_SEQPACKET) {
switch (ax25->state) {
we add decrements of refcounts in ax25_release(), and use lock_sock() to do synchronization.
If refcounts decrease in ax25_release(), the decrements of refcounts in ax25_kill_by_device()
will not be executed and vice versa.
1. If we decrease the refcounts in ax25_release(), the decrements of refcounts in
ax25_kill_by_device() will not execute. Because we set NULL to sk->sk_wq in sock_orphan()
and we check whether sk->sk_wq is NULL in ax25_kill_by_device(). Only positions (3) and (4)
could execute.
(Thread 1) |
ax25_bind() |
... |
ax25_addr_ax25dev() |
ax25_dev_hold() //(1) |
... |
dev_hold_track() //(2) | (Thread 2)
... | ax25_release()
| ...
| lock_sock(sk)
| sock_orphan(sk)
| sk->sk_wq = NULL //set NULL
| ...
| if (ax25_dev) {
| dev_put_track() //(3)
| ax25_dev_put() //(4)
|
(thread 3) |
ax25_kill_by_device() |
... |
lock_sock(sk) |
s->ax25_dev = NULL |
if (sk->sk_wq) { //check |
dev_put_track() //(5) |
ax25_dev_put() //(6) |
2. If we decrease refcounts in ax25_kill_by_device(), the decrements of refcounts
in ax25_release() will not execute. Because we set NULL to s->ax25_dev in ax25_kill_by_device()
and we check whether ax25_dev is NULL in ax25_release(). Only positions (3) and (4)
could execute.
(Thread 1) |
ax25_bind() |
... |
ax25_addr_ax25dev() |
ax25_dev_hold() //(1) |
... |
dev_hold_track() //(2) | (Thread 2)
... | ax25_kill_by_device()
| ...
| lock_sock(sk)
| s->ax25_dev = NULL //set NULL
| if (sk->sk_wq) {
| dev_put_track() //(3)
| ax25_dev_put() //(4)
| ...
|
(thread 3) |
ax25_release() |
... |
lock_sock(sk); |
sock_orphan(sk); |
... |
if (ax25_dev) { //check |
dev_put_track() //(5) |
ax25_dev_put() //(6) |
> > I sent "[PATCH net V2 1/2] ax25: Fix refcount leaks caused by ax25_cb_del()"
> > on On Fri, Mar 11, 2022. Could this patch solve your question?
>
> I had a bunch of questions... You just ignored them, and sent a patch
> called v2 instead of v4 so I was puzzled and confused. I guess the
> answer is no, could you please answer the questions?
I hope my answer could solve your questions. If you still have any questions
welcome to send email to me. I will send "[PATCH net V4 1/2] ax25: Fix
refcount leaks caused by ax25_cb_del()" as soon as possible.
What`s more, I found NPD bugs in ax25 timers, I will send
"[PATCH net V4 2/2] ax25: Fix NULL pointer dereferences in ax25 timers" together.
Best wishes,
Duoming Zhou
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