linux-kernel - Re: [PATCH][scsi-next] scsi: lpfc: fix null pointer dereference on nvmebuf

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Date:   Wed, 11 Jul 2018 16:50:25 +0200
From:   Tomas Henzl <thenzl@...hat.com>
To:     Colin King <colin.king@...onical.com>,
        James Smart <james.smart@...adcom.com>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][scsi-next] scsi: lpfc: fix null pointer dereference on
 nvmebuf

On 07/11/2018 03:44 PM, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
>
> The check of nvmebuf suggests that it can be null, however a recent
> change dereferences it to determine oxid before it is null checked,
> hence there is a potential null deference on the pointer.  Fix this
> by performing the null check first.  Also remove the oxid from the
> debug log message as this is no longer valid.  I considered an early
> fetch of oxid if nvmebuf was valid, however, what oxid should be set
> to if nvembuf is null could lead to an ambiguous logging of an invalid
> oxid, so I thought just removing it from the logging was the least
> confusion solution.

I think that the 'if (!nvmebuf)' test is not needed and it would be better to remove the
tests (it is tested for the second time later in the function).
Tomas

>
> Detected by CoverityScan, CID#1471753 ("Dereference before null check")
>
> Fixes: 68c9b55deea5 ("scsi: lpfc: Fix abort error path for NVMET")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/scsi/lpfc/lpfc_nvmet.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/scsi/lpfc/lpfc_nvmet.c b/drivers/scsi/lpfc/lpfc_nvmet.c
> index 22f8a204b69f..01652d9ac619 100644
> --- a/drivers/scsi/lpfc/lpfc_nvmet.c
> +++ b/drivers/scsi/lpfc/lpfc_nvmet.c
> @@ -1742,12 +1742,9 @@ lpfc_nvmet_unsol_ls_buffer(struct lpfc_hba *phba, struct lpfc_sli_ring *pring,
>  	uint32_t *payload;
>  	uint32_t size, oxid, sid, rc;
>  
> -	fc_hdr = (struct fc_frame_header *)(nvmebuf->hbuf.virt);
> -	oxid = be16_to_cpu(fc_hdr->fh_ox_id);
> -
>  	if (!nvmebuf || !phba->targetport) {
>  		lpfc_printf_log(phba, KERN_ERR, LOG_NVME_IOERR,
> -				"6154 LS Drop IO x%x\n", oxid);
> +				"6154 LS Drop IO\n");
>  		oxid = 0;
>  		size = 0;
>  		sid = 0;
> @@ -1755,6 +1752,9 @@ lpfc_nvmet_unsol_ls_buffer(struct lpfc_hba *phba, struct lpfc_sli_ring *pring,
>  		goto dropit;
>  	}
>  
> +	fc_hdr = (struct fc_frame_header *)(nvmebuf->hbuf.virt);
> +	oxid = be16_to_cpu(fc_hdr->fh_ox_id);
> +
>  	tgtp = (struct lpfc_nvmet_tgtport *)phba->targetport->private;
>  	payload = (uint32_t *)(nvmebuf->dbuf.virt);
>  	size = bf_get(lpfc_rcqe_length,  &nvmebuf->cq_event.cqe.rcqe_cmpl);