Re: [PATCH v2][next] scsi: lpfc: Avoid -Wstringop-overflow warning

[Justin Tee]

Thanks Gustavo and Kees.

Reviewed-by: Justin Tee <justin.tee@xxxxxxxxxxxx>

On Thu, Jun 1, 2023 at 4:43 PM Gustavo A. R. Silva
<gustavoars@xxxxxxxxxx> wrote:
>
> Prevent any potential integer wrapping issue, and avoid a
> -Wstringop-overflow warning by using the check_mul_overflow() helper.
>
> drivers/scsi/lpfc/lpfc.h:
> 837:#define LPFC_RAS_MIN_BUFF_POST_SIZE (256 * 1024)
>
> drivers/scsi/lpfc/lpfc_debugfs.c:
> 2266 size = LPFC_RAS_MIN_BUFF_POST_SIZE * phba->cfg_ras_fwlog_buffsize;
>
> this can wrap to negative if cfg_ras_fwlog_buffsize is large
> enough. And even when in practice this is not possible (due to
> phba->cfg_ras_fwlog_buffsize never being larger than 4[1]), the
> compiler is legitimately warning us about potentially buggy code.
>
> Fix the following warning seen under GCC-13:
> In function ‘lpfc_debugfs_ras_log_data’,
>     inlined from ‘lpfc_debugfs_ras_log_open’ at drivers/scsi/lpfc/lpfc_debugfs.c:2271:15:
> drivers/scsi/lpfc/lpfc_debugfs.c:2210:25: warning: ‘memcpy’ specified bound between 18446744071562067968 and 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Wstringop-overflow=]
>  2210 |                         memcpy(buffer + copied, dmabuf->virt,
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  2211 |                                size - copied - 1);
>       |                                ~~~~~~~~~~~~~~~~~~
>
> Link: https://github.com/KSPP/linux/issues/305
> Link: https://lore.kernel.org/linux-hardening/CABPRKS8zyzrbsWt4B5fp7kMowAZFiMLKg5kW26uELpg1cDKY3A@xxxxxxxxxxxxxx/ [1]
> Co-developed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> ---
> Changes in v2:
>  - Use check_mul_overflow() helper (Kees).
>
> v1:
>  - Link: https://lore.kernel.org/linux-hardening/ZHZq7AV9Q2WG1xRB@work/
>
>  drivers/scsi/lpfc/lpfc_debugfs.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/lpfc/lpfc_debugfs.c b/drivers/scsi/lpfc/lpfc_debugfs.c
> index bdf34af4ef36..7f9b221e7c34 100644
> --- a/drivers/scsi/lpfc/lpfc_debugfs.c
> +++ b/drivers/scsi/lpfc/lpfc_debugfs.c
> @@ -2259,11 +2259,15 @@ lpfc_debugfs_ras_log_open(struct inode *inode, struct file *file)
>                 goto out;
>         }
>         spin_unlock_irq(&phba->hbalock);
> -       debug = kmalloc(sizeof(*debug), GFP_KERNEL);
> +
> +       if (check_mul_overflow(LPFC_RAS_MIN_BUFF_POST_SIZE,
> +                              phba->cfg_ras_fwlog_buffsize, &size))
> +               goto out;
> +
> +       debug = kzalloc(sizeof(*debug), GFP_KERNEL);
>         if (!debug)
>                 goto out;
>
> -       size = LPFC_RAS_MIN_BUFF_POST_SIZE * phba->cfg_ras_fwlog_buffsize;
>         debug->buffer = vmalloc(size);
>         if (!debug->buffer)
>                 goto free_debug;
> --
> 2.34.1
>