linux-kernel - Re: [RFC PATCH] RDMA/srp: Fix use-after-free in srp_exit_cmd

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Message-ID: <5a4a42fe-c5c8-63fe-365f-e6c74a279cc2@acm.org>
Date:   Fri, 24 Jun 2022 16:26:06 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Li Zhijian <lizhijian@...itsu.com>
Cc:     Leon Romanovsky <leon@...nel.org>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] RDMA/srp: Fix use-after-free in srp_exit_cmd_priv

On 6/24/22 15:59, Jason Gunthorpe wrote:
> I don't even understand how get_device() prevents this call chain??
> 
> It looks to me like the problem is srp_remove_one() is not waiting for
> or canceling some outstanding work.

Hi Jason,

My conclusions from the call traces in Li's email are as follows:
* scsi_host_dev_release() can get called after srp_remove_one().
* srp_exit_cmd_priv() uses the ib_device pointer. If srp_remove_one() is 
called before srp_exit_cmd_priv() then a use-after-free is triggered.

Is calling get_device() and put_device() on the struct ib_device an 
acceptable way to fix this? If so, I recommend to insert a get_device() 
call after the scsi_add_host() call and put_device() calls after the two 
scsi_remove_host() calls instead of merging the patch at the start of 
this email thread.

Thanks,

Bart.