linux-kernel - Re: [PATCH v2] scsi: target: pscsi: Fix possible null-pointer dereference in pscsi_complete

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Date:   Tue, 10 Aug 2021 09:18:41 +0200
From:   Bodo Stroesser <bostroesser@...il.com>
To:     Tuo Li <islituo@...il.com>, martin.petersen@...cle.com
Cc:     linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org, baijiaju1990@...il.com,
        TOTE Robot <oslab@...nghua.edu.cn>
Subject: Re: [PATCH v2] scsi: target: pscsi: Fix possible null-pointer
 dereference in pscsi_complete_cmd()

On 10.08.21 06:04, Tuo Li wrote:
> The return value of transport_kmap_data_sg() is assigned to the variable
> buf:
>    buf = transport_kmap_data_sg(cmd);
> 
> And then it is checked:
>    if (!buf) {
> 
> This indicates that buf can be NULL. However, it is dereferenced in the
> following statements:
>    if (!(buf[3] & 0x80))
>      buf[3] |= 0x80;
>    if (!(buf[2] & 0x80))
>      buf[2] |= 0x80;
> 
> To fix these possible null-pointer dereferences, dereference buf and call
> transport_kunmap_data_sg() only when buf is not NULL.
> 
> Reported-by: TOTE Robot <oslab@...nghua.edu.cn>
> Signed-off-by: Tuo Li <islituo@...il.com>
> ---
> v2:
> * Put transport_kunmap_data_sg() into the else-branch of the if (!bug).
>    Thank Bodo Stroesser for helpful advice.
> ---
>   drivers/target/target_core_pscsi.c | 18 +++++++++---------
>   1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
> index 2629d2ef3970..75ef52f008ff 100644
> --- a/drivers/target/target_core_pscsi.c
> +++ b/drivers/target/target_core_pscsi.c
> @@ -620,17 +620,17 @@ static void pscsi_complete_cmd(struct se_cmd *cmd, u8 scsi_status,
>   			buf = transport_kmap_data_sg(cmd);
>   			if (!buf) {
>   				; /* XXX: TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE */
> -			}
> -
> -			if (cdb[0] == MODE_SENSE_10) {
> -				if (!(buf[3] & 0x80))
> -					buf[3] |= 0x80;
>   			} else {
> -				if (!(buf[2] & 0x80))
> -					buf[2] |= 0x80;
> -			}
> +				if (cdb[0] == MODE_SENSE_10) {
> +					if (!(buf[3] & 0x80))
> +						buf[3] |= 0x80;
> +				} else {
> +					if (!(buf[2] & 0x80))
> +						buf[2] |= 0x80;
> +				}
>   
> -			transport_kunmap_data_sg(cmd);
> +				transport_kunmap_data_sg(cmd);
> +			}
>   		}
>   	}
>   after_mode_sense:
> 

Reviewed-by: Bodo Stroesser <bostroesser@...il.com>

Regards,
Bodo