linux-kernel - Re: [PATCH] scsi: be_iscsi: fix possible memory leak and refactor code

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Date:	Mon, 18 Nov 2013 17:51:44 -0200
From:	Geyslan Gregório Bem <geyslan@...il.com>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	Jayamohan Kallickal <jayamohan.kallickal@...lex.com>,
	"open list:SERVER ENGINES 10..." <linux-scsi@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scsi: be_iscsi: fix possible memory leak and refactor code

2013/11/18 Geyslan Gregório Bem <geyslan@...il.com>:
> 2013/11/18 James Bottomley <James.Bottomley@...senpartnership.com>:
>> On Mon, 2013-11-18 at 14:18 -0200, Geyslan Gregório Bem wrote:
>>> 2013/11/18 James Bottomley <James.Bottomley@...senpartnership.com>:
>>> > On Sun, 2013-11-17 at 23:12 -0200, Geyslan Gregório Bem wrote:
>>> >> 2013/11/17 James Bottomley <James.Bottomley@...senpartnership.com>:
>>> >> > On Sun, 2013-11-17 at 19:09 -0200, Geyslan Gregório Bem wrote:
>>> >> >> 2013/11/17 James Bottomley <James.Bottomley@...senpartnership.com>:
>>> >> >> > On Sun, 2013-11-17 at 15:51 -0300, Geyslan G. Bem wrote:
>>> >> >> >> This patch fix memory leakage in cases 'ISCSI_NET_PARAM_VLAN_ID' and
>>> >> >> >> 'ISCSI_NET_PARAM_VLAN_PRIORITY' and refactors code 'going out' when
>>> >> >> >> necessary.
>>> >> >> >
>>> >> >> > You pointlessly renamed a variable, which makes the diff hard to read.
>>> >> >> > Please don't do that.
>>> >> >>
>>> >> >> Ok, I can agree. 'len' means length? What is returned in case of non
>>> >> >> error?
>>> >> >
>>> >> > it returns the length of buf written to or negative error.
>>> >> >
>>> >> >> > You missed the fact that the passed in pointer is unmodified if
>>> >> >> > mgmt_get_if_info() returns non zero, so the kfree frees junk and would
>>> >> >> > oops.
>>> >> >> >
>>> >> >> > There's no need for a goto; len = -EINVAL; does everything that's
>>> >> >> > needed.
>>> >> >>
>>> >> >> Well, that is a coverity catch. CID 1128954. Check it.
>>> >> >
>>> >> > I didn't say coverity was wrong, I said your patch was (well not wrong,
>>> >> > just over complex and incomplete).  This is the way to fix both
>>> >> > problems.
>>> >> >
>>> >> > James
>>> >> >
>>> >> > ---
>>> >> >
>>> >> > diff --git a/drivers/scsi/be2iscsi/be_iscsi.c b/drivers/scsi/be2iscsi/be_iscsi.c
>>> >> > index ffadbee..9dcbdfa 100644
>>> >> > --- a/drivers/scsi/be2iscsi/be_iscsi.c
>>> >> > +++ b/drivers/scsi/be2iscsi/be_iscsi.c
>>> >> > @@ -541,10 +541,8 @@ static int be2iscsi_get_if_param(struct beiscsi_hba *phba,
>>> >> >                 ip_type = BE2_IPV6;
>>> >>
>>> >> James, this approach will not prevent the leakage.
>>> >
>>> > I don't see why not.  The -EINVAL case goes through the kfree() now too,
>>> > no?
>>>
>>> I'm refering to the removal of kfree in your suggestion.
>>
>> That's the second bug I pointed out via code inspection.  If the
>> function returns an error (any non zero return) then the pointer isn't
>> altered, so we return without the free.  It's a standard error pattern.
>
> Ok. So kfree is useless until the code go to the function bail. Right?
>
>>
>>> >
>>> >>  We can initialize the if_info with NULL and always kfree it without
>>> >> to care about junk.
>>> >
>>> > Why?  Error return means no allocation.
>>> Setting if_info to NULL allow to kfree without concerns.
>>>
>>> Eg.:
>>>
>>> - struct be_cmd_get_if_info_resp *if_info;
>>> + struct be_cmd_get_if_info_resp *if_info = NULL;
>>>
>>> ...
>>>
>>> +       if (len)
>>> +               goto out;
>>>
>>> ...
>>>
>>> -               if (if_info->vlan_priority == BEISCSI_VLAN_DISABLE)
>>> -                       return -EINVAL;
>>> +               if (if_info->vlan_priority == BEISCSI_VLAN_DISABLE) {
>>> +                       len = -EINVAL;
>>> +                       goto out;
>>> +               }
>>
>> What's the point of that?  Just removing the goto out; has the code
>> going to the same place because of the break below.
>>
>> James
>>
>>
>
> I agree whit you that the code goes to same place with or without goto
> out. It's just a pattern to simplify future changes in the function.
>
> But I can remove it if you want.
>
>
> --
> Regards,
>
> Geyslan G. Bem
> hackingbits.com

Done:
[PATCH v2] scsi: be_iscsi: fix possible memory leak


-- 
Regards,

Geyslan G. Bem
hackingbits.com
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