linux-hardening - [PATCH v2] bus: mhi: ep: Use kcalloc() instead of kzalloc()

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Date: Sun, 28 Jan 2024 12:27:22 +0100
From: Erick Archer <erick.archer@....com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Jeffrey Hugo <quic_jhugo@...cinc.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Dan Carpenter <error27@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alex Elder <elder@...aro.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Erick Archer <erick.archer@....com>,
	linux-arm-msm@...r.kernel.org,
	mhi@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH v2] bus: mhi: ep: Use kcalloc() instead of kzalloc()

This is an effort to get rid of all multiplications from allocation
functions in order to prevent integer overflows [1].

Here the multiplication is obviously safe because the "event_rings"
member never can have a value greater than 255 (8 bits). This member
is set twice using always FIELD_GET:

mhi_cntrl->event_rings = FIELD_GET(MHICFG_NER_MASK, regval);
mhi_cntrl->event_rings = FIELD_GET(MHICFG_NER_MASK, regval);

And the MHICFG_NER_MASK macro defines the 8 bits mask that guarantees
a maximum value of 255.

However, using kcalloc() is more appropriate [1] and improves
readability. This patch has no effect on runtime behavior.

Link: https://github.com/KSPP/linux/issues/162 [1]
Link: https://www.kernel.org/doc/html/next/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Signed-off-by: Erick Archer <erick.archer@....com>
---
Changes in v2:
- Add more info in the commit message to better explain the change.
  (Dan Carpenter)
- Add the "Reviewed-by:" tag.

Previous versions:
v1 - https://lore.kernel.org/linux-hardening/20240120152518.13006-1-erick.archer@gmx.com/
---
 drivers/bus/mhi/ep/main.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
index 65fc1d738bec..8d7a4102bdb7 100644
--- a/drivers/bus/mhi/ep/main.c
+++ b/drivers/bus/mhi/ep/main.c
@@ -1149,8 +1149,9 @@ int mhi_ep_power_up(struct mhi_ep_cntrl *mhi_cntrl)
 	mhi_ep_mmio_mask_interrupts(mhi_cntrl);
 	mhi_ep_mmio_init(mhi_cntrl);

-	mhi_cntrl->mhi_event = kzalloc(mhi_cntrl->event_rings * (sizeof(*mhi_cntrl->mhi_event)),
-					GFP_KERNEL);
+	mhi_cntrl->mhi_event = kcalloc(mhi_cntrl->event_rings,
+				       sizeof(*mhi_cntrl->mhi_event),
+				       GFP_KERNEL);
 	if (!mhi_cntrl->mhi_event)
 		return -ENOMEM;

--
2.25.1