[PATCH 4.19 003/422] scsi: core: Handle drivers which set sg_tablesize to zero

[Greg Kroah-Hartman]

From: Michael Schmitz <schmitzmic@xxxxxxxxx>

commit 9393c8de628cf0968d81a17cc11841e42191e041 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.

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 ("scsi:
cxlflash: Set sg_tablesize to 1 instead of SG_NONE"), 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
calculating 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.

CC: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1572922150-4358-1-git-send-email-schmitzmic@xxxxxxxxx
Signed-off-by: Michael Schmitz <schmitzmic@xxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>


---
 drivers/scsi/scsi_lib.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2371,7 +2371,8 @@ int scsi_mq_setup_tags(struct Scsi_Host
 {
 	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;