This is a note to let you know that I've just added the patch titled
ax25: Fix refcount imbalance on inbound connections
to the 6.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ax25-fix-refcount-imbalance-on-inbound-connections.patch
and it can be found in the queue-6.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 6092a21f3f6dda8dad72966bfd716109dc49050e
Author: Lars Kellogg-Stedman <lars@xxxxxxxxxx>
Date: Wed May 29 17:02:43 2024 -0400
ax25: Fix refcount imbalance on inbound connections
[ Upstream commit 3c34fb0bd4a4237592c5ecb5b2e2531900c55774 ]
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 will start with one of the
following errors:
refcount_t: decrement hit 0; leaking memory.
refcount_t: underflow; use-after-free.
And will then have a trace 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 (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(). This makes the
logic leading to ax25_accept() match the logic for ax25_bind(): in both
cases we increment the refcount, which is ultimately decremented in
ax25_release().
Fixes: 9fd75b66b8f6 ("ax25: Fix refcount leaks caused by ax25_cb_del()")
Signed-off-by: Lars Kellogg-Stedman <lars@xxxxxxxxxx>
Tested-by: Duoming Zhou <duoming@xxxxxxxxxx>
Tested-by: Dan Cross <crossd@xxxxxxxxx>
Tested-by: Chris Maness <christopher.maness@xxxxxxxxx>
Reviewed-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240529210242.3346844-2-lars@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 9169efb2f43aa..5fff5930e4deb 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, int flags,
{
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, int flags,
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);
