commit 9393c8de628c upstream

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.d, and an empty message aborts the commit.

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.

Backport of commit 9393c8de628c to stable kernels before 4.19 which lack commit 3dccdf53c2f3 ("scsi: core: avoid preallocating big SGL for data"), as requestef by Sasha Levin.

Signed-off-by: Michael Schmitz schmitzmic@gmail.com Cc: Finn Thain fthain@telegraphics.com.au Cc: Sasha Levin sashal@kernel.org Cc: Martin K. Petersen martin.petersen@oracle.com --- 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 0adfb3b..e0a4ad9 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -2356,7 +2356,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost) { unsigned int cmd_size, sgl_size;

- sgl_size = scsi_mq_sgl_size(shost); + sgl_size = max_t(unsigned int, sizeof(struct scatterlist), + scsi_mq_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) + sgl_size;