linux-kernel - Re: [PATCH 2/3] scsi: libiscsi: fix invalid pointer dereference in iscsi_eh_session

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Date:   Fri, 10 Sep 2021 11:38:51 -0500
From:   Mike Christie <michael.christie@...cle.com>
To:     Ding Hui <dinghui@...gfor.com.cn>, lduncan@...e.com,
        cleech@...hat.com, jejb@...ux.ibm.com, martin.petersen@...cle.com,
        open-iscsi@...glegroups.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] scsi: libiscsi: fix invalid pointer dereference in
 iscsi_eh_session_reset

On 9/9/21 8:02 PM, Ding Hui wrote:
> like commit 5db6dd14b313 ("scsi: libiscsi: Fix NULL pointer dereference in
> iscsi_eh_session_reset"), access conn->persistent_address here is not safe
> too.
> 
> The persistent_address is independent of conn refcount, so maybe
> already freed by iscsi_conn_teardown(), also we put the refcount of conn
> above, the conn pointer may be invalid.

This shouldn't happen like you describe above, because when we wake up
we will see the session->state is ISCSI_STATE_TERMINATE. We will then
not reference the conn in that code below.

However, it looks like we could hit an issue where if a user was resetting
the persistent_address or targetname via iscsi_set_param -> iscsi_switch_str_param
then we could be accessing freed memory. I think we need the frwd_lock when swapping
the strings in iscsi_switch_str_param.


> 
> Signed-off-by: Ding Hui <dinghui@...gfor.com.cn>
> ---
>  drivers/scsi/libiscsi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
> index 712a45368385..69b3b2148328 100644
> --- a/drivers/scsi/libiscsi.c
> +++ b/drivers/scsi/libiscsi.c
> @@ -2531,8 +2531,8 @@ int iscsi_eh_session_reset(struct scsi_cmnd *sc)
>  	spin_lock_bh(&session->frwd_lock);
>  	if (session->state == ISCSI_STATE_LOGGED_IN) {
>  		ISCSI_DBG_EH(session,
> -			     "session reset succeeded for %s,%s\n",
> -			     session->targetname, conn->persistent_address);
> +			     "session reset succeeded for %s\n",
> +			     session->targetname);
>  	} else
>  		goto failed;
>  	spin_unlock_bh(&session->frwd_lock);
>