linux-kernel - Re: [PATCH] scsi: isci: initialize shost fully before calling scsi_add

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Date:   Tue, 8 Jan 2019 14:30:36 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Logan Gunthorpe <logang@...tatee.com>, linux-scsi@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Intel SCU Linux support <intel-linux-scu@...el.com>,
        Artur Paszkiewicz <artur.paszkiewicz@...el.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH] scsi: isci: initialize shost fully before calling
 scsi_add_host()

On 1/8/19 1:50 PM, Logan Gunthorpe wrote:
> scsi_mq_setup_tags(), which is called by scsi_add_host(), calculates
> the command size to allocate based on the prot_capabilities. In the
> isci driver, scsi_host_set_prot() is called after scsi_add_host()
> so the command size gets calculated to be smaller than it needs to be.
> Eventually, scsi_mq_init_request() locates the 'prot_sdb' after the command
> assuming it was sized correctly and a buffer overrun may occur.
> 
> However, seeing blk_mq_alloc_rqs() rounds up to the nearest cache line
> size, the mistake can go unnoticed.
> 
> The bug was noticed after the struct request size was reduced by
> commit 9d037ad707ed ("block: remove req->timeout_list")
> 
> Which likely reduced the allocated space for the request by an entire
> cache line, enough that the overflow could be hit and it caused a panic,
> on boot, at:
> 
>   RIP: 0010:t10_pi_complete+0x77/0x1c0
>   Call Trace:
>     <IRQ>
>     sd_done+0xf5/0x340
>     scsi_finish_command+0xc3/0x120
>     blk_done_softirq+0x83/0xb0
>     __do_softirq+0xa1/0x2e6
>     irq_exit+0xbc/0xd0
>     call_function_single_interrupt+0xf/0x20
>     </IRQ>
> 
> sd_done() would call scsi_prot_sg_count() which reads the number of
> entities in 'prot_sdb', but seeing 'prot_sdb' is located after the end of
> the allocated space it reads a garbage number and erroneously calls
> t10_pi_complete().
> 
> To prevent this, the calls to scsi_host_set_prot() are moved into
> isci_host_alloc() before the call to scsi_add_host(). Out of caution,
> also move the similar call to scsi_host_set_guard().

Nice work!

Reviewed-by: Jens Axboe <axboe@...nel.dk>

-- 
Jens Axboe