[PATCH v2] scsi: advansys: Prefer struct_size over open coded arithmetic

[Len Baker <len.baker@gmx.com>]

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, use the struct_size() helper to do the arithmetic instead of the
argument "size + count * size" in the kzalloc() function.

This code was detected with the help of Coccinelle and audited and fixed
manually.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@gmx.com>
---
Changelog v1 -> v2
- Rebase against v5.15-rc2
- Remove the unnecessary "size" variable (Gustavo A. R. Silva).
- Update the commit changelog to inform that this code was detected
  using a Coccinelle script (Gustavo A. R. Silva).

 drivers/scsi/advansys.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/advansys.c b/drivers/scsi/advansys.c
index ffb391967573..e341b3372482 100644
--- a/drivers/scsi/advansys.c
+++ b/drivers/scsi/advansys.c
@@ -7477,8 +7477,8 @@ static int asc_build_req(struct asc_board *boardp, struct scsi_cmnd *scp,
 			return ASC_ERROR;
 		}

-		asc_sg_head = kzalloc(sizeof(asc_scsi_q->sg_head) +
-			use_sg * sizeof(struct asc_sg_list), GFP_ATOMIC);
+		asc_sg_head = kzalloc(struct_size(asc_sg_head, sg_list, use_sg),
+				      GFP_ATOMIC);
 		if (!asc_sg_head) {
 			scsi_dma_unmap(scp);
 			set_host_byte(scp, DID_SOFT_ERROR);
--
2.25.1