linux-kernel - Re: [PATCH] target: iscsi: iscsi_target_tpg: Fix a possible null-pointer dereference in iscsit_tpg_add_network

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Date:   Mon, 29 Jul 2019 08:02:42 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, martin.petersen@...cle.com,
        kstewart@...uxfoundation.org, allison@...utok.net,
        rfontana@...hat.com, tglx@...utronix.de, gregkh@...uxfoundation.org
Cc:     linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] target: iscsi: iscsi_target_tpg: Fix a possible
 null-pointer dereference in iscsit_tpg_add_network_portal()

On Mon, 2019-07-29 at 10:29 +0800, Jia-Ju Bai wrote:
> In iscsit_tpg_add_network_portal(), there is an if statement on line
> 496
> to check whether tpg->tpg_tiqn is NULL:
>     if (tpg->tpg_tiqn)
> 
> When tpg->tpg_tiqn is NULL, it is used on line 508:
>     pr_debug(..., tpg->tpg_tiqn->tiqn, ...);
> 
> Thus, a possible null-pointer dereference may occur.
> 
> To fix this bug, tpg->tpg_tiqn is checked before being used.
> 
> This bug is found by a static analysis tool STCheck written by us.

I don't really think this is helpful.  The first question is, is the
implied might be NULL check correct?  The tpg_tiqn is always set by a
non-dummy driver and I think network configuration is only done for the
non dummy driver, so I suspect the NULL check is wrong.  Secondly even
if the NULL check were correct, I think there's still a need for some
debugging output, so the proposed patch also looks wrong.

James