Re: [PATCH][next] scsi: cxgb4i: fix dereference of pointer tdata before it is null checked

[Varun Prakash <varun@chelsio.com>]

On Thu, Jul 09, 2020 at 02:52:17PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> Currently pointer tdata is being dereferenced on the initialization of
> pointer skb before tdata is null checked. This could lead to a potential
> null pointer dereference.  Fix this by dereferencing tdata after tdata
> has been null pointer sanity checked.
> 
> Addresses-Coverity: ("Dereference before null check")
> Fixes: e33c2482289b ("scsi: cxgb4i: Add support for iSCSI segmentation offload")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/scsi/cxgbi/libcxgbi.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/cxgbi/libcxgbi.c b/drivers/scsi/cxgbi/libcxgbi.c
> index 1fb101c616b7..a6119d9daedf 100644
> --- a/drivers/scsi/cxgbi/libcxgbi.c
> +++ b/drivers/scsi/cxgbi/libcxgbi.c
> @@ -2147,7 +2147,7 @@ int cxgbi_conn_init_pdu(struct iscsi_task *task, unsigned int offset,
>  	struct iscsi_conn *conn = task->conn;
>  	struct iscsi_tcp_task *tcp_task = task->dd_data;
>  	struct cxgbi_task_data *tdata = iscsi_task_cxgbi_data(task);
> -	struct sk_buff *skb = tdata->skb;
> +	struct sk_buff *skb;
>  	struct scsi_cmnd *sc = task->sc;
>  	u32 expected_count, expected_offset;
>  	u32 datalen = count, dlimit = 0;
> @@ -2161,6 +2161,7 @@ int cxgbi_conn_init_pdu(struct iscsi_task *task, unsigned int offset,
>  		       tcp_task ? tcp_task->dd_data : NULL, tdata);
>  		return -EINVAL;
>  	}
> +	skb = tdata->skb;
>  
>  	log_debug(1 << CXGBI_DBG_ISCSI | 1 << CXGBI_DBG_PDU_TX,
>  		  "task 0x%p,0x%p, skb 0x%p, 0x%x,0x%x,0x%x, %u+%u.\n",
> @@ -2365,7 +2366,7 @@ int cxgbi_conn_xmit_pdu(struct iscsi_task *task)
>  	struct iscsi_tcp_task *tcp_task = task->dd_data;
>  	struct cxgbi_task_data *tdata = iscsi_task_cxgbi_data(task);
>  	struct cxgbi_task_tag_info *ttinfo = &tdata->ttinfo;
> -	struct sk_buff *skb = tdata->skb;
> +	struct sk_buff *skb;
>  	struct cxgbi_sock *csk = NULL;
>  	u32 pdulen = 0;
>  	u32 datalen;
> @@ -2378,6 +2379,7 @@ int cxgbi_conn_xmit_pdu(struct iscsi_task *task)
>  		return -EINVAL;
>  	}
>  
> +	skb = tdata->skb;
>  	if (!skb) {
>  		log_debug(1 << CXGBI_DBG_ISCSI | 1 << CXGBI_DBG_PDU_TX,
>  			  "task 0x%p, skb NULL.\n", task);

Acked-by: Varun Prakash <varun@chelsio.com>