On Tue, 5 Nov 2019, Michael Schmitz wrote:
> In scsi_mq_setup_tags(), cmd_size is calculated based on zero size
> for the scatter-gather list in case the low level driver uses SG_NONE
> in its host template.
>
> cmd_size is passed on to the block layer for calculation of the request
> size, and we've seen NULL pointer dereference errors from the block
> layer in drivers where SG_NONE is used and a mq IO scheduler is active,
> apparently as a consequence of this (see commit 68ab2d76e4be for the
> cxflash driver, and a recent patch by Finn Thain converting the three
> m68k NFR5380 drivers to avoid setting SG_NONE).
>
> Try to avoid these errors by accounting for at least one sg list entry
> when caculating cmd_size, regardless of whether the low level driver
> set a zero sg_tablesize.
>
> Tested on 030 m68k with the atari_scsi driver - setting sg_tablesize to
> SG_NONE no longer results in a crash when loading this driver.
>
> Signed-off-by: Michael Schmitz <schmitzmic@xxxxxxxxx>
> CC: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>
No objections from me. I still like the patch series I sent but it's a
matter of taste. I'm happy to leave it to the scsi maintainers to figure
out the best fix for this regression.
--
> ---
> drivers/scsi/scsi_lib.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index d47d637..d38b0e1 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1867,7 +1867,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
> {
> unsigned int cmd_size, sgl_size;
>
> - sgl_size = scsi_mq_inline_sgl_size(shost);
> + sgl_size = max_t(unsigned int, sizeof(struct scatterlist),
> + scsi_mq_inline_sgl_size(shost));
> cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size + sgl_size;
> if (scsi_host_get_prot(shost))
> cmd_size += sizeof(struct scsi_data_buffer) +
>
