linux-kernel - Re: [PATCH] scsi: sni_53c710: Fix a resource leak in an error handling path

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Date:   Thu, 20 May 2021 19:50:05 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     jejb@...ux.ibm.com, martin.petersen@...cle.com,
        James.Bottomley@...elEye.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] scsi: sni_53c710: Fix a resource leak in an error
 handling path

Le 20/05/2021 à 17:06, Thomas Bogendoerfer a écrit :
> On Thu, May 20, 2021 at 06:44:25AM +0200, Christophe JAILLET wrote:
>> After a successful 'NCR_700_detect()' call, 'NCR_700_release()' must be
>> called to release some DMA related resources, as already done in the
>> remove function.
>>
>> Fixes: c27d85f3f3c5 ("[SCSI] SNI RM 53c710 driver")
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
>> ---
>>   drivers/scsi/sni_53c710.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/scsi/sni_53c710.c b/drivers/scsi/sni_53c710.c
>> index 678651b9b4dd..f6d60d542207 100644
>> --- a/drivers/scsi/sni_53c710.c
>> +++ b/drivers/scsi/sni_53c710.c
>> @@ -98,6 +98,7 @@ static int snirm710_probe(struct platform_device *dev)
>>   
>>    out_put_host:
>>   	scsi_host_put(host);
>> +	NCR_700_release(host);
> 
> shouldn't this done before the scsi_host_put() to avoid a use after free ?

I did it this way because remove function are:
    scsi_remove_host
    NCR_700_release

The other reason was to free resources in the reverse order than allocation.
But this logic does'nt work in all cases.

> lasi700.c has the same problem.

and a400t.c and bvme6000_scsi.c and mvme16x_scsi.c and sim710.c and 
zorro7xx.c.
That is to say all drivers that use NCR_700_detect().

That is why I'm unsure with my patch. It is unusual to have ALL users 
wrong. It is more likely that I missed something and that the code is 
correct.

I also don't fully understand why we use 'scsi_host_put' in some place 
and 'scsi_remove_host' in remove functions.
Referenced managed resources sometimes have the needed mechanism to 
automagically release some resource.

> And it looks like NCR_700_detect() will leak
> dma memory, if scsi_host_alloc() failed.

Agreed. And same if scsi_add_host fails at the end of the function.

> 
> Thomas.
>