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

From: Len Baker <len.baker@gmx.com>
To: Matthew Wilcox <willy@infradead.org>,
	Hannes Reinecke <hare@suse.com>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Len Baker <len.baker@gmx.com>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	linux-hardening@vger.kernel.org, linux-scsi@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH] scsi: advansys: Prefer struct_size over open coded arithmetic
Date: Sat, 18 Sep 2021 13:18:05 +0200	[thread overview]
Message-ID: <20210918111805.15471-1-len.baker@gmx.com> (raw)

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, refactor the code a bit to use the struct_size() helper instead of
the argument "size + count * size" in the kzalloc() function.

[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>
---
 drivers/scsi/advansys.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/advansys.c b/drivers/scsi/advansys.c
index ffb391967573..fe882502e7bf 100644
--- a/drivers/scsi/advansys.c
+++ b/drivers/scsi/advansys.c
@@ -7465,6 +7465,7 @@ static int asc_build_req(struct asc_board *boardp, struct scsi_cmnd *scp,
 		return ASC_BUSY;
 	} else if (use_sg > 0) {
 		int sgcnt;
+		size_t size;
 		struct scatterlist *slp;
 		struct asc_sg_head *asc_sg_head;

@@ -7477,8 +7478,8 @@ 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);
+		size = struct_size(asc_scsi_q->sg_head, sg_list, use_sg);
+		asc_sg_head = kzalloc(size, GFP_ATOMIC);
 		if (!asc_sg_head) {
 			scsi_dma_unmap(scp);
 			set_host_byte(scp, DID_SOFT_ERROR);
--
2.25.1

