RE: [PATCH] usb: gadget: composite: Fix null pointer exception

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> -----Original Message-----
> From: Peter Chen <peter.chen@xxxxxxxxxx>
> Sent: Monday, November 1, 2021 9:19 PM
> To: 胡启航(Nick Hu) <huqihang@xxxxxxxx>
> Cc: balbi@xxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH] usb: gadget: composite: Fix null pointer exception
> 
> On 21-11-01 09:57:57, Qihang Hu wrote:
> > In the config_ep_by_speed_and_alt function, select the corresponding
> > descriptor through g->speed, but the interface driver
> 
> function driver
> 
> > may not
> > support the corresponding speed. So, we need to check whether the
> > interface 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@xxxxxxxx>
> > ---
> >  drivers/usb/gadget/composite.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> > index 72a9797dbbae..443a65af98af 100644
> > --- a/drivers/usb/gadget/composite.c
> > +++ b/drivers/usb/gadget/composite.c
> > @@ -166,21 +166,21 @@ int config_ep_by_speed_and_alt(struct usb_gadget
> *g,
> >  	/* select desired speed */
> >  	switch (g->speed) {
> >  	case USB_SPEED_SUPER_PLUS:
> > -		if (gadget_is_superspeed_plus(g)) {
> > +		if (gadget_is_superspeed_plus(g) && f->ssp_descriptors) {
> >  			speed_desc = f->ssp_descriptors;
> >  			want_comp_desc = 1;
> >  			break;
> >  		}
> >  		fallthrough;
> >  	case USB_SPEED_SUPER:
> > -		if (gadget_is_superspeed(g)) {
> > +		if (gadget_is_superspeed(g) && f->ss_descriptors) {
> >  			speed_desc = f->ss_descriptors;
> >  			want_comp_desc = 1;
> >  			break;
> >  		}
> >  		fallthrough;
> >  	case USB_SPEED_HIGH:
> > -		if (gadget_is_dualspeed(g)) {
> > +		if (gadget_is_dualspeed(g) && f->hs_descriptors) {
> >  			speed_desc = f->hs_descriptors;
> >  			break;
> >  		}
> > --
> > 2.25.1
> >
> 
> Besides your fix, you may show an warning that said "the function
> doesn't hold the descriptors for supported speed, using the default (FS)
> descriptors". See below kernel doc for detail.
> 
> /**
>  * config_ep_by_speed_and_alt() - configures the given endpoint
>  *
>  * ....
>  * Note: the supplied function should hold all the descriptors
>  * for supported speeds
>  */
> 
> What's more, you may fix android f_audio_source.c, and let it support
> super speed and super speed plus.
> 
> --
> 
> Thanks,
> Peter Chen



>From 9b8262792b6e85e6060601dbfc651b1e75b649f0 Mon Sep 17 00:00:00 2001
From: Qihang Hu <huqihang@xxxxxxxx>
Date: Sat, 30 Oct 2021 16:11:38 +0800
Subject: [PATCH] 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@xxxxxxxx>
---
 drivers/usb/gadget/composite.c | 39 ++++++++++++++++++++++------------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 72a9797dbbae..4f0d81f561ae 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -151,9 +151,11 @@ int config_ep_by_speed_and_alt(struct usb_gadget *g,
 				struct usb_ep *_ep,
 				u8 alt)
 {
+	struct usb_composite_dev *cdev;
 	struct usb_endpoint_descriptor *chosen_desc = NULL;
 	struct usb_interface_descriptor *int_desc = NULL;
 	struct usb_descriptor_header **speed_desc = NULL;
+	int incomplete_desc = 0;
 
 	struct usb_ss_ep_comp_descriptor *comp_desc = NULL;
 	int want_comp_desc = 0;
@@ -167,28 +169,43 @@ 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 function doesn't hold all the descriptors for supported speep\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 +261,8 @@ 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


Thanks for your suggestion, this is my revised patch.
Of course, I will continue to fix android f_audio_source.c to solve the problem fundamentally.

Thanks




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