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Message-ID: <20231207064244.22412-1-kuniyu@amazon.com>
Date: Thu, 7 Dec 2023 15:42:44 +0900
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <v4bel@...ori.io>
CC: <davem@...emloft.net>, <dhowells@...hat.com>, <edumazet@...gle.com>,
<horms@...nel.org>, <imv4bel@...il.com>, <kuba@...nel.org>,
<lukas.bulwahn@...il.com>, <mkl@...gutronix.de>, <netdev@...r.kernel.org>,
<pabeni@...hat.com>, <kuniyu@...zon.com>
Subject: Re: [PATCH] appletalk: Fix Use-After-Free in atalk_ioctl
From: Hyunwoo Kim <v4bel@...ori.io>
Date: Wed, 6 Dec 2023 04:09:23 -0800
> Because atalk_ioctl() accesses sk->sk_receive_queue
> without holding a sk->sk_receive_queue.lock, it can
> cause a race with atalk_recvmsg().
> A use-after-free for skb occurs with the following flow.
> ```
> atalk_ioctl() -> skb_peek()
> atalk_recvmsg() -> skb_recv_datagram() -> skb_free_datagram()
> ```
> Add sk->sk_receive_queue.lock to atalk_ioctl() to fix this issue.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Hyunwoo Kim <v4bel@...ori.io>
> ---
> net/appletalk/ddp.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
> index 9ba04a69ec2a..f240d5338bc9 100644
> --- a/net/appletalk/ddp.c
> +++ b/net/appletalk/ddp.c
> @@ -1775,15 +1775,16 @@ static int atalk_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
> break;
> }
> case TIOCINQ: {
> + long amount = 0;
> /*
> * These two are safe on a single CPU system as only
> * user tasks fiddle here
> */
> + spin_lock_irq(&sk->sk_receive_queue.lock);
nit: please call spin_lock() after declaring all variables; otherwise
checkpatch.pl will complain.
> struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
> - long amount = 0;
Also, please keep the reverse xmas tree.
> -
> if (skb)
> amount = skb->len - sizeof(struct ddpehdr);
> + spin_unlock_irq(&sk->sk_receive_queue.lock);
> rc = put_user(amount, (int __user *)argp);
> break;
> }
> --
> 2.25.1
>
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