6.6-stable review patch. If anyone has any objections, please let me know.
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From: Lars Kellogg-Stedman lars@oddbit.com
[ 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@oddbit.com Tested-by: Duoming Zhou duoming@zju.edu.cn Tested-by: Dan Cross crossd@gmail.com Tested-by: Chris Maness christopher.maness@gmail.com Reviewed-by: Dan Carpenter dan.carpenter@linaro.org Link: https://lore.kernel.org/r/20240529210242.3346844-2-lars@oddbit.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@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 9d11d26e46c0e..26a3095bec462 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);