[PATCH] nvmet: prefer struct_size over open coded arithmetic

[Len Baker]

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.

In this case this is not actually dynamic size: all the operands
involved in the calculation are constant values. However it is better to
refactor this anyway, just to keep the open-coded math idiom out of
code.

So, use the struct_size() helper to do the arithmetic instead of the
argument "size + count * size" in the kmalloc() 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@xxxxxxx>
---
Hi,

this patch is built against the linux-next tree (tag next-20211015).

Regards,
Len

 drivers/nvme/target/admin-cmd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/target/admin-cmd.c b/drivers/nvme/target/admin-cmd.c
index aa6d84d8848e..4aa71625c86a 100644
--- a/drivers/nvme/target/admin-cmd.c
+++ b/drivers/nvme/target/admin-cmd.c
@@ -278,8 +278,8 @@ static void nvmet_execute_get_log_page_ana(struct nvmet_req *req)
 	u16 status;

 	status = NVME_SC_INTERNAL;
-	desc = kmalloc(sizeof(struct nvme_ana_group_desc) +
-			NVMET_MAX_NAMESPACES * sizeof(__le32), GFP_KERNEL);
+	desc = kmalloc(struct_size(desc, nsids, NVMET_MAX_NAMESPACES),
+		       GFP_KERNEL);
 	if (!desc)
 		goto out;

--
2.25.1