From: Lars Kellogg-Stedman <lars@oddbit.com>
To: linux-hams@vger.kernel.org
Subject: [PATCH RFC] ax25: Fix (more) netdev refcount issues
Date: Fri, 26 Apr 2024 17:29:40 -0400 [thread overview]
Message-ID: <6kant25vimoq36blyb5sjqgq3xxjcqbqeskbgf5zihdho3iulb@ni2lvhiytfrg> (raw)
Folks,
I'm posting the following patch here before sending it to netdev in the
hopes that someone can take a look at the change and comment on the
correctness. This resolves all of the issues I've been experiencing
recently with ax.25.
...
When closing a socket, the ax.25 code releases references via
netdev_put() and ax25_dev_put(). In the case when the socket was the
result of an incoming connection, these references were never allocated in
the first place, causing underflows in both ax25_dev->refcount and
ax25_dev->dev->refcnt_tracker->untracked. This would result in a variety of
errors:
- After an initial connection and then again after several subsequent
connections:
refcount_t: decrement hit 0; leaking memory.
- After several subsequent connections:
refcount_t: underflow; use-after-free.
A typical call trace for the above two issues would look like:
Call Trace:
<TASK>
? show_regs+0x64/0x70
? __warn+0x83/0x120
? refcount_warn_saturate+0xb2/0x100
? report_bug+0x158/0x190
? prb_read_valid+0x20/0x30
? handle_bug+0x3e/0x70
? exc_invalid_op+0x1c/0x70
? asm_exc_invalid_op+0x1f/0x30
? refcount_warn_saturate+0xb2/0x100
? refcount_warn_saturate+0xb2/0x100
ax25_release+0x2ad/0x360
__sock_release+0x35/0xa0
sock_close+0x19/0x20
[...]
On reboot, the kernel would get stuck in an infinite loop:
unregister_netdevice: waiting for ax1 to become free. Usage count = 0
The attached patch corrects all three of the above problems by ensuring
that we call netdev_hold() and ax25_dev_hold() for incoming connections.
Signed-off-by: Lars Kellogg-Stedman <lars@oddbit.com>
---
net/ax25/ax25_in.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/ax25/ax25_in.c b/net/ax25/ax25_in.c
index 1cac25aca63..35a55ad05f2 100644
--- a/net/ax25/ax25_in.c
+++ b/net/ax25/ax25_in.c
@@ -411,6 +411,8 @@ static int ax25_rcv(struct sk_buff *skb, struct net_device *dev,
ax25->state = AX25_STATE_3;
ax25_cb_add(ax25);
+ netdev_hold(ax25_dev->dev, &ax25->dev_tracker, GFP_ATOMIC);
+ ax25_dev_hold(ax25_dev);
ax25_start_heartbeat(ax25);
ax25_start_t3timer(ax25);
--
2.44.0
--
Lars Kellogg-Stedman <lars@oddbit.com> | larsks @ {irc,twitter,github}
http://blog.oddbit.com/ | N1LKS
next reply other threads:[~2024-04-26 23:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 21:29 Lars Kellogg-Stedman [this message]
2024-04-27 8:48 ` [PATCH RFC] ax25: Fix (more) netdev refcount issues Dan Carpenter
2024-04-27 17:15 ` Lars Kellogg-Stedman
2024-04-28 11:01 ` Dan Carpenter
2024-04-29 18:06 ` Lars Kellogg-Stedman
2024-04-30 10:08 ` Dan Carpenter
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