Hi Kees,

On Sun, Aug 22, 2021 at 07:59:51AM -0700, Kees Cook wrote:

On Sun, Aug 22, 2021 at 04:28:20PM +0200, Len Baker wrote:

quoted

Dynamic 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 purpose specific kcalloc() function instead of the argument
size * count in the kzalloc() function.

It might be useful to reference the documentation on why this change is
desired:
https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Ok, I will add this info to the next version. Thanks for the advise.

Here and in the docs, though, it's probably worth noting that these
aren't actually dynamic sizes: both sides of the multiplication are
constant values. I still think it's best to refactor these anyway, just
to keep the open-coded math idiom out of code, though.

Ok, I will change the commit message to note this. Also I will send
a patch to add this info to the documentation.

Also, have you looked at Coccinelle at all? I have a hideous pile of
rules that try to find these instances, but it really needs improvement:
https://github.com/kees/coccinelle-linux-allocator-overflow/tree/trunk/array_size

I think my script is even worst ;) but find some arithmetic to improve :)
I will take a look. Thanks for the info.

Reviewed-by: Kees Cook <redacted>

Regards,
Len

quoted

Signed-off-by: Len Baker <redacted>
---
 drivers/staging/rtl8192u/r819xU_phy.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/rtl8192u/r819xU_phy.c b/drivers/staging/rtl8192u/r819xU_phy.c
index ff6fe2ee3349..97f4d89500ae 100644
--- a/drivers/staging/rtl8192u/r819xU_phy.c
+++ b/drivers/staging/rtl8192u/r819xU_phy.c

@@ -1195,17 +1195,17 @@ static u8 rtl8192_phy_SwChnlStepByStep(struct net_device *dev, u8 channel,
 	u8 e_rfpath;
 	bool ret;

-	pre_cmd = kzalloc(sizeof(*pre_cmd) * MAX_PRECMD_CNT, GFP_KERNEL);
+	pre_cmd = kcalloc(MAX_PRECMD_CNT, sizeof(*pre_cmd), GFP_KERNEL);
 	if (!pre_cmd)
 		return false;

-	post_cmd = kzalloc(sizeof(*post_cmd) * MAX_POSTCMD_CNT, GFP_KERNEL);
+	post_cmd = kcalloc(MAX_POSTCMD_CNT, sizeof(*post_cmd), GFP_KERNEL);
 	if (!post_cmd) {
 		kfree(pre_cmd);
 		return false;
 	}

-	rf_cmd = kzalloc(sizeof(*rf_cmd) * MAX_RFDEPENDCMD_CNT, GFP_KERNEL);
+	rf_cmd = kcalloc(MAX_RFDEPENDCMD_CNT, sizeof(*rf_cmd), GFP_KERNEL);
 	if (!rf_cmd) {
 		kfree(pre_cmd);
 		kfree(post_cmd);
--

2.25.1

--
Kees Cook