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Message-ID: <20240522183133.729159-2-lars@oddbit.com>
Date: Wed, 22 May 2024 14:31:34 -0400
From: lars@...bit.com
To: linux-hams@...r.kernel.org,
netdev@...r.kernel.org
Cc: Lars Kellogg-Stedman <lars@...bit.com>
Subject: [PATCH v4] ax25: Fix refcount imbalance on inbound connections
From: Lars Kellogg-Stedman <lars@...bit.com>
When releasing a socket in ax25_release(), we call netdev_put() to
decrease the refcount on the associated ax.25 device. However, the
execution path for accepting an incoming connection never calls
netdev_hold(). This imbalance leads to refcount errors, and ultimately
to kernel crashes.
A typical call trace for the above situation looks like this:
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 (or any attempt to remove the interface), the kernel gets
stuck in an infinite loop:
unregister_netdevice: waiting for ax0 to become free. Usage count = 0
This patch corrects these issues by ensuring that we call netdev_hold()
and ax25_dev_hold() for new connections in ax25_accept().
Fixes: 7d8a3a477b ("ax25: Fix ax25 session cleanup problems")
Signed-off-by: Lars Kellogg-Stedman <lars@...bit.com>
---
v3:
- Address naveenm's comments regarding the ordering of variable declarations
(https://lore.kernel.org/netdev/SJ2PR18MB5635B7ADC7339BEDB79B183DA2EA2@SJ2PR18MB5635.namprd18.prod.outlook.com/)
v4:
- respond to kuba's comments regarding the Fixes: tag
(https://lore.kernel.org/netdev/20240522100701.4d9edf99@kernel.org/)
net/ax25/af_ax25.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 8077cf2ee44..d6f9fae06a9 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1378,8 +1378,10 @@ static int ax25_accept(struct socket *sock, struct socket *newsock,
{
struct sk_buff *skb;
struct sock *newsk;
+ ax25_dev *ax25_dev;
DEFINE_WAIT(wait);
struct sock *sk;
+ ax25_cb *ax25;
int err = 0;
if (sock->state != SS_UNCONNECTED)
@@ -1434,6 +1436,10 @@ static int ax25_accept(struct socket *sock, struct socket *newsock,
kfree_skb(skb);
sk_acceptq_removed(sk);
newsock->state = SS_CONNECTED;
+ ax25 = sk_to_ax25(newsk);
+ ax25_dev = ax25->ax25_dev;
+ netdev_hold(ax25_dev->dev, &ax25->dev_tracker, GFP_ATOMIC);
+ ax25_dev_hold(ax25_dev);
out:
release_sock(sk);
--
2.45.1
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