linux-kernel - Re: use-after-free in srpt_enable

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Message-ID: <2e8b080c-cda5-9224-1e46-95fb0b4f7036@acm.org>
Date:   Tue, 5 Jul 2022 09:10:31 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Mike Christie <michael.christie@...cle.com>,
        "lizhijian@...itsu.com" <lizhijian@...itsu.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: use-after-free in srpt_enable_tpg()

On 7/5/22 04:40, Hillf Danton wrote:
> If no compat devices can be added to ib_device with DEVICE_REGISTERED
> cleared then they can be removed without ib_device's refcount dropping
> to zero.
> Even if that is not strictly true, a new flag that marks ib device
> disabled and prevents new compact devices from being added can be added
> in bid to cut the wait for completion.
> 
> Hillf
> 
> +++ b/drivers/infiniband/core/device.c
> @@ -1265,6 +1265,7 @@ static void disable_device(struct ib_dev
>   
>   	down_write(&devices_rwsem);
>   	xa_clear_mark(&devices, device->index, DEVICE_REGISTERED);
> +	// device->disabled = true;
>   	up_write(&devices_rwsem);
>   
>   	/*
> @@ -1282,17 +1283,10 @@ static void disable_device(struct ib_dev
>   	}
>   
>   	ib_cq_pool_cleanup(device);
> +	remove_compat_devs(device);
>   
>   	/* Pairs with refcount_set in enable_device */
>   	ib_device_put(device);
> -	wait_for_completion(&device->unreg_completion);
> -
> -	/*
> -	 * compat devices must be removed after device refcount drops to zero.
> -	 * Otherwise init_net() may add more compatdevs after removing compat
> -	 * devices and before device is disabled.
> -	 */
> -	remove_compat_devs(device);
>   }

I'm not convinced the above patch is a step in the right direction nor 
that it is correct. Anyway, since the RDMA maintainers know this code 
better than I do I will let them comment on the above patch.

Bart.