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

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Date:	Mon, 18 Nov 2013 14:18:46 -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 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.

>
>>  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;
+               }

...

        case ISCSI_NET_PARAM_VLAN_PRIORITY:
-               if (if_info->vlan_priority == BEISCSI_VLAN_DISABLE)
-                       return -EINVAL;
+               if (if_info->vlan_priority == BEISCSI_VLAN_DISABLE) {
+                       len = -EINVAL;
+                       goto out;
+               }


+out:
        kfree(if_info);
        return len;


Thus, if if_info remains NULL (was not allocated after
mgmt_get_if_info call) kfree returns without oops. And we can
centralize the freeing in the out regarding chapter 7 of coding style
(http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/CodingStyle#n386).

What do you think?

>
> James
>
>



-- 
Regards,

Geyslan G. Bem
hackingbits.com
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