[PATCH v2] usb: mtu3: fix possible NULL pointer dereference in ep0_rx_state()

[PATCH v2] usb: mtu3: fix possible NULL pointer dereference in ep0_rx_state()

[Pavel Zhigulin]

The function 'ep0_rx_state()' accessed 'mreq->request' before verifying
that mreq was valid. If 'next_ep0_request()' returned NULL, this could
lead to a NULL pointer dereference. The return value of
'next_ep0_request()' is checked in every other code path except
here. It appears that the intended 'if (mreq)' check was mistakenly
written as 'if (req)', since the req pointer cannot be NULL when mreq
is not NULL.

Initialize 'mreq' and 'req' to NULL by default, and switch 'req'
NULL-checking to 'mreq' non-NULL check to prevent invalid memory access.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: df2069acb005 ("usb: Add MediaTek USB3 DRD driver")
Signed-off-by: Pavel Zhigulin <Pavel.Zhigulin@kaspersky.com>
---
v2: Add <stable@vger.kernel.org> to CC list
v1: https://lore.kernel.org/all/20251027193152.3906497-1-Pavel.Zhigulin@kaspersky.com

 drivers/usb/mtu3/mtu3_gadget_ep0.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/mtu3/mtu3_gadget_ep0.c b/drivers/usb/mtu3/mtu3_gadget_ep0.c
index e4fd1bb14a55..ee7466ca4d99 100644
--- a/drivers/usb/mtu3/mtu3_gadget_ep0.c
+++ b/drivers/usb/mtu3/mtu3_gadget_ep0.c
@@ -508,8 +508,8 @@ static int handle_standard_request(struct mtu3 *mtu,
 /* receive an data packet (OUT) */
 static void ep0_rx_state(struct mtu3 *mtu)
 {
-	struct mtu3_request *mreq;
-	struct usb_request *req;
+	struct mtu3_request *mreq = NULL;
+	struct usb_request *req = NULL;
 	void __iomem *mbase = mtu->mac_base;
 	u32 maxp;
 	u32 csr;
@@ -519,10 +519,11 @@ static void ep0_rx_state(struct mtu3 *mtu)

 	csr = mtu3_readl(mbase, U3D_EP0CSR) & EP0_W1C_BITS;
 	mreq = next_ep0_request(mtu);
-	req = &mreq->request;

 	/* read packet and ack; or stall because of gadget driver bug */
-	if (req) {
+	if (mreq) {
+		req = &mreq->request;
+
 		void *buf = req->buf + req->actual;
 		unsigned int len = req->length - req->actual;

--
2.43.0

Re: [PATCH v2] usb: mtu3: fix possible NULL pointer dereference in ep0_rx_state()

[kernel test robot]

Hi,

Thanks for your patch.

FYI: kernel test robot notices the stable kernel rule is not satisfied.

The check is based on https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-1

Rule: add the tag "Cc: stable@vger.kernel.org" in the sign-off area to have the patch automatically included in the stable tree.
Subject: [PATCH v2] usb: mtu3: fix possible NULL pointer dereference in ep0_rx_state()
Link: https://lore.kernel.org/stable/20251111140956.3285945-1-Pavel.Zhigulin%40kaspersky.com

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