linux-kernel - [PATCH v2] usb: gadget: composite: Fix null pointer exception

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Date:   Fri,  5 Nov 2021 18:48:40 +0800
From:   Qihang Hu <huqihang@...o.com>
To:     balbi@...nel.org, gregkh@...uxfoundation.org, peter.chen@...nel.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Qihang Hu <huqihang@...o.com>
Subject: [PATCH v2] usb: gadget: composite: Fix null pointer exception

In the config_ep_by_speed_and_alt function, select the corresponding
descriptor through g->speed, but the function driver may not
support the corresponding speed. So, we need to check whether the
function driver provides the corresponding speed descriptor when
selecting the descriptor.

[  237.708146]  android_work: sent uevent USB_STATE=CONNECTED
[  237.712464]  kconfigfs-gadget gadget: super-speed config #1: b
[  237.712487]  kUnable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[  237.712493]  kMem abort info:
[  237.712498]  k  ESR = 0x96000006
[  237.712504]  k  EC = 0x25: DABT (current EL), IL = 32 bits
[  237.712510]  k  SET = 0, FnV = 0
[  237.712515]  k  EA = 0, S1PTW = 0
[  237.712520]  kData abort info:
[  237.712525]  k  ISV = 0, ISS = 0x00000006
[  237.712530]  k  CM = 0, WnR = 0
[  237.712536]  kuser pgtable: 4k pages, 39-bit VAs, pgdp=000000020ef29000
[  237.712541]  k[0000000000000000] pgd=000000020ef2a003, pud=000000020ef2a003, pmd=0000000000000000
[  237.712554]  kInternal error: Oops: 96000006 [#1] PREEMPT SMP
[  237.722067]  kSkip md ftrace buffer dump for: 0x1609e0
[  237.787037]  kWorkqueue: dwc_wq dwc3_bh_work.cfi_jt
[  237.854922]  kpstate: 60c00085 (nZCv daIf +PAN +UAO)
[  237.863165]  kpc : config_ep_by_speed_and_alt+0x90/0x308
[  237.871766]  klr : audio_set_alt+0x54/0x78
[  237.879108]  ksp : ffffffc0104839e0

Signed-off-by: Qihang Hu <huqihang@...o.com>
---
Changes in v2:
-Add warning message
---
 drivers/usb/gadget/composite.c | 40 +++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 13 deletions(-)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 72a9797dbbae..746b34cf0310 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -160,6 +160,9 @@ int config_ep_by_speed_and_alt(struct usb_gadget *g,
 
 	struct usb_descriptor_header **d_spd; /* cursor for speed desc */
 
+	struct usb_composite_dev *cdev;
+	int incomplete_desc = 0;
+
 	if (!g || !f || !_ep)
 		return -EIO;
 
@@ -167,28 +170,43 @@ int config_ep_by_speed_and_alt(struct usb_gadget *g,
 	switch (g->speed) {
 	case USB_SPEED_SUPER_PLUS:
 		if (gadget_is_superspeed_plus(g)) {
-			speed_desc = f->ssp_descriptors;
-			want_comp_desc = 1;
-			break;
+			if (f->ssp_descriptors) {
+				speed_desc = f->ssp_descriptors;
+				want_comp_desc = 1;
+				break;
+			}
+			incomplete_desc = 1;
 		}
 		fallthrough;
 	case USB_SPEED_SUPER:
 		if (gadget_is_superspeed(g)) {
-			speed_desc = f->ss_descriptors;
-			want_comp_desc = 1;
-			break;
+			if (f->ss_descriptors) {
+				speed_desc = f->ss_descriptors;
+				want_comp_desc = 1;
+				break;
+			}
+			incomplete_desc = 1;
 		}
 		fallthrough;
 	case USB_SPEED_HIGH:
 		if (gadget_is_dualspeed(g)) {
-			speed_desc = f->hs_descriptors;
-			break;
+			if (f->hs_descriptors) {
+				speed_desc = f->hs_descriptors;
+				break;
+			}
+			incomplete_desc = 1;
 		}
 		fallthrough;
 	default:
 		speed_desc = f->fs_descriptors;
 	}
 
+	cdev = get_gadget_data(g);
+	if (incomplete_desc != 0)
+		WARNING(cdev,
+			"%s doesn't hold the descriptors for current speed\n",
+			f->name);
+
 	/* find correct alternate setting descriptor */
 	for_each_desc(speed_desc, d_spd, USB_DT_INTERFACE) {
 		int_desc = (struct usb_interface_descriptor *)*d_spd;
@@ -244,12 +262,8 @@ int config_ep_by_speed_and_alt(struct usb_gadget *g,
 			_ep->maxburst = comp_desc->bMaxBurst + 1;
 			break;
 		default:
-			if (comp_desc->bMaxBurst != 0) {
-				struct usb_composite_dev *cdev;
-
-				cdev = get_gadget_data(g);
+			if (comp_desc->bMaxBurst != 0)
 				ERROR(cdev, "ep0 bMaxBurst must be 0\n");
-			}
 			_ep->maxburst = 1;
 			break;
 		}
-- 
2.25.1