[syzbot] [sound?] general protection fault in snd_scarlett2_init

[syzbot] [sound?] general protection fault in snd_scarlett2_init

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    bb375c251ab4 dt-bindings: usb: st,st-ohci-300x: convert to..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
console output: https://syzkaller.appspot.com/x/log.txt?x=138f1b5a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f1500201919951cc
dashboard link: https://syzkaller.appspot.com/bug?extid=ae893a8901067fde2741
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14ffb006580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12ebbb5a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2475c3172471/disk-bb375c25.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/30449aa672dd/vmlinux-bb375c25.xz
kernel image: https://storage.googleapis.com/syzbot-assets/46d3937d1c16/bzImage-bb375c25.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ae893a8901067fde2741@syzkaller.appspotmail.com

usb 4-1: 0:6 : does not exist
usb 4-1: 0:7 : does not exist
usb 4-1: 0:8 : does not exist
usb 4-1: 0:9 : does not exist
usb 4-1: 0:10 : does not exist
usb 4-1: Focusrite Scarlett Gen 3 Mixer Driver enabled (pid=0x8215); report any issues to https://github.com/geoffreybennett/scarlett-gen2/issues
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 1 UID: 0 PID: 28 Comm: kworker/1:1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: usb_hub_wq hub_event
RIP: 0010:usb_endpoint_num include/uapi/linux/usb/ch9.h:479 [inline]
RIP: 0010:scarlett2_find_fc_interface sound/usb/mixer_scarlett2.c:8261 [inline]
RIP: 0010:scarlett2_init_private sound/usb/mixer_scarlett2.c:8295 [inline]
RIP: 0010:snd_scarlett2_controls_create sound/usb/mixer_scarlett2.c:8684 [inline]
RIP: 0010:snd_scarlett2_init.cold+0xbad/0x6c79 sound/usb/mixer_scarlett2.c:9407
Code: 84 c0 74 06 0f 8e ca 0b 00 00 48 8b 44 24 20 48 8d 7b 02 48 89 fa 40 88 a8 48 02 00 00 b8 ff ff 37 00 48 c1 ea 03 48 c1 e0 2a <0f> b6 04 02 48 89 fa 83 e2 07 38 d0 7f 08 84 c0 0f 85 9e 0b 00 00
RSP: 0018:ffffc900001e68d8 EFLAGS: 00010286
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81543c4b
RDX: 0000000000000000 RSI: ffffffff81543c5d RDI: 0000000000000002
RBP: 0000000000000001 R08: 0000000000000001 R09: 00000000000000ff
R10: 00000000000000ff R11: 0000000000000000 R12: ffff88811dd24804
R13: dffffc0000000000 R14: ffff88811dd248a8 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8882687d3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000558c34efbe88 CR3: 00000000094ae000 CR4: 00000000003506f0
Call Trace:
 <TASK>
 snd_usb_mixer_apply_create_quirk+0x1c21/0x2b80 sound/usb/mixer_quirks.c:4446
 snd_usb_create_mixer+0x7a2/0x1910 sound/usb/mixer.c:3641
 usb_audio_probe+0xf6d/0x3a90 sound/usb/card.c:1033
 usb_probe_interface+0x303/0x8f0 drivers/usb/core/driver.c:396
 call_driver_probe drivers/base/dd.c:583 [inline]
 really_probe+0x241/0xa60 drivers/base/dd.c:661
 __driver_probe_device+0x1de/0x400 drivers/base/dd.c:803
 driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:833
 __device_attach_driver+0x1ff/0x3e0 drivers/base/dd.c:961
 bus_for_each_drv+0x159/0x1e0 drivers/base/bus.c:500
 __device_attach+0x1e4/0x4d0 drivers/base/dd.c:1033
 device_initial_probe+0xaf/0xd0 drivers/base/dd.c:1088
 bus_probe_device+0x64/0x160 drivers/base/bus.c:574
 device_add+0x11d9/0x1950 drivers/base/core.c:3689
 usb_set_configuration+0xd97/0x1c60 drivers/usb/core/message.c:2208
 usb_generic_driver_probe+0xa1/0xe0 drivers/usb/core/generic.c:250
 usb_probe_device+0xef/0x400 drivers/usb/core/driver.c:291
 call_driver_probe drivers/base/dd.c:583 [inline]
 really_probe+0x241/0xa60 drivers/base/dd.c:661
 __driver_probe_device+0x1de/0x400 drivers/base/dd.c:803
 driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:833
 __device_attach_driver+0x1ff/0x3e0 drivers/base/dd.c:961
 bus_for_each_drv+0x159/0x1e0 drivers/base/bus.c:500
 __device_attach+0x1e4/0x4d0 drivers/base/dd.c:1033
 device_initial_probe+0xaf/0xd0 drivers/base/dd.c:1088
 bus_probe_device+0x64/0x160 drivers/base/bus.c:574
 device_add+0x11d9/0x1950 drivers/base/core.c:3689
 usb_new_device.cold+0x685/0x115c drivers/usb/core/hub.c:2695
 hub_port_connect drivers/usb/core/hub.c:5567 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5707 [inline]
 port_event drivers/usb/core/hub.c:5871 [inline]
 hub_event+0x314d/0x4af0 drivers/usb/core/hub.c:5953
 process_one_work+0x9d7/0x1920 kernel/workqueue.c:3275
 process_scheduled_works kernel/workqueue.c:3358 [inline]
 worker_thread+0x5da/0xe40 kernel/workqueue.c:3439
 kthread+0x370/0x450 kernel/kthread.c:467
 ret_from_fork+0x6c3/0xcb0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:usb_endpoint_num include/uapi/linux/usb/ch9.h:479 [inline]
RIP: 0010:scarlett2_find_fc_interface sound/usb/mixer_scarlett2.c:8261 [inline]
RIP: 0010:scarlett2_init_private sound/usb/mixer_scarlett2.c:8295 [inline]
RIP: 0010:snd_scarlett2_controls_create sound/usb/mixer_scarlett2.c:8684 [inline]
RIP: 0010:snd_scarlett2_init.cold+0xbad/0x6c79 sound/usb/mixer_scarlett2.c:9407
Code: 84 c0 74 06 0f 8e ca 0b 00 00 48 8b 44 24 20 48 8d 7b 02 48 89 fa 40 88 a8 48 02 00 00 b8 ff ff 37 00 48 c1 ea 03 48 c1 e0 2a <0f> b6 04 02 48 89 fa 83 e2 07 38 d0 7f 08 84 c0 0f 85 9e 0b 00 00
RSP: 0018:ffffc900001e68d8 EFLAGS: 00010286

RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81543c4b
RDX: 0000000000000000 RSI: ffffffff81543c5d RDI: 0000000000000002
RBP: 0000000000000001 R08: 0000000000000001 R09: 00000000000000ff
R10: 00000000000000ff R11: 0000000000000000 R12: ffff88811dd24804
R13: dffffc0000000000 R14: ffff88811dd248a8 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8882687d3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4cb1355900 CR3: 00000001175e2000 CR4: 00000000003506f0
----------------
Code disassembly (best guess):
   0:	84 c0                	test   %al,%al
   2:	74 06                	je     0xa
   4:	0f 8e ca 0b 00 00    	jle    0xbd4
   a:	48 8b 44 24 20       	mov    0x20(%rsp),%rax
   f:	48 8d 7b 02          	lea    0x2(%rbx),%rdi
  13:	48 89 fa             	mov    %rdi,%rdx
  16:	40 88 a8 48 02 00 00 	mov    %bpl,0x248(%rax)
  1d:	b8 ff ff 37 00       	mov    $0x37ffff,%eax
  22:	48 c1 ea 03          	shr    $0x3,%rdx
  26:	48 c1 e0 2a          	shl    $0x2a,%rax
* 2a:	0f b6 04 02          	movzbl (%rdx,%rax,1),%eax <-- trapping instruction
  2e:	48 89 fa             	mov    %rdi,%rdx
  31:	83 e2 07             	and    $0x7,%edx
  34:	38 d0                	cmp    %dl,%al
  36:	7f 08                	jg     0x40
  38:	84 c0                	test   %al,%al
  3a:	0f 85 9e 0b 00 00    	jne    0xbde


---
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[PATCH] ALSA: usb-audio: Add the number of endpoints checked was 0

[Edward Adam Davis]

The user constructed a corrupted USB device, causing the USB device
enumeration phase to fail to resolve any endpoints. This resulted in
a null pointer dereference reported in [1] when the USB sound card
driver executed probe to initialize the mixer. 

To avoid the problem reported in [1], a check was added to ensure that
the number of endpoints contained in the interface was 0 when checking
the mixer status.

[1]
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
RIP: 0010:usb_endpoint_num include/uapi/linux/usb/ch9.h:479 [inline]
RIP: 0010:scarlett2_find_fc_interface sound/usb/mixer_scarlett2.c:8261 [inline]
RIP: 0010:scarlett2_init_private sound/usb/mixer_scarlett2.c:8295 [inline]
RIP: 0010:snd_scarlett2_controls_create sound/usb/mixer_scarlett2.c:8684 [inline]
RIP: 0010:snd_scarlett2_init.cold+0xbad/0x6c79 sound/usb/mixer_scarlett2.c:9407
Call Trace:
 snd_usb_mixer_apply_create_quirk+0x1c21/0x2b80 sound/usb/mixer_quirks.c:4446
 snd_usb_create_mixer+0x7a2/0x1910 sound/usb/mixer.c:3641
 usb_audio_probe+0xf6d/0x3a90 sound/usb/card.c:1033

Reported-by: syzbot+ae893a8901067fde2741@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ae893a8901067fde2741 
Tested-by: syzbot+ae893a8901067fde2741@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 sound/usb/mixer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index ac8c71ba9483..bd28caec3004 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -3563,8 +3563,12 @@ static int snd_usb_mixer_status_create(struct usb_mixer_interface *mixer)
 	int buffer_length;
 	unsigned int epnum;
 
+	epnum = get_iface_desc(mixer->hostif)->bNumEndpoints;
+	if (epnum == 0)
+		return -EINVAL;
+
 	/* we need one interrupt input endpoint */
-	if (get_iface_desc(mixer->hostif)->bNumEndpoints < 1)
+	if (epnum < 1)
 		return 0;
 	ep = get_endpoint(mixer->hostif, 0);
 	if (!usb_endpoint_dir_in(ep) || !usb_endpoint_xfer_int(ep))
-- 
2.43.0

Re: [PATCH] ALSA: usb-audio: Add the number of endpoints checked was 0

[Takashi Iwai]

On Mon, 09 Mar 2026 08:32:29 +0100,
Edward Adam Davis wrote:
> 
> The user constructed a corrupted USB device, causing the USB device
> enumeration phase to fail to resolve any endpoints. This resulted in
> a null pointer dereference reported in [1] when the USB sound card
> driver executed probe to initialize the mixer. 
> 
> To avoid the problem reported in [1], a check was added to ensure that
> the number of endpoints contained in the interface was 0 when checking
> the mixer status.
> 
> [1]
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> RIP: 0010:usb_endpoint_num include/uapi/linux/usb/ch9.h:479 [inline]
> RIP: 0010:scarlett2_find_fc_interface sound/usb/mixer_scarlett2.c:8261 [inline]
> RIP: 0010:scarlett2_init_private sound/usb/mixer_scarlett2.c:8295 [inline]
> RIP: 0010:snd_scarlett2_controls_create sound/usb/mixer_scarlett2.c:8684 [inline]
> RIP: 0010:snd_scarlett2_init.cold+0xbad/0x6c79 sound/usb/mixer_scarlett2.c:9407
> Call Trace:
>  snd_usb_mixer_apply_create_quirk+0x1c21/0x2b80 sound/usb/mixer_quirks.c:4446
>  snd_usb_create_mixer+0x7a2/0x1910 sound/usb/mixer.c:3641
>  usb_audio_probe+0xf6d/0x3a90 sound/usb/card.c:1033
> 
> Reported-by: syzbot+ae893a8901067fde2741@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=ae893a8901067fde2741 
> Tested-by: syzbot+ae893a8901067fde2741@syzkaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  sound/usb/mixer.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> index ac8c71ba9483..bd28caec3004 100644
> --- a/sound/usb/mixer.c
> +++ b/sound/usb/mixer.c
> @@ -3563,8 +3563,12 @@ static int snd_usb_mixer_status_create(struct usb_mixer_interface *mixer)
>  	int buffer_length;
>  	unsigned int epnum;
>  
> +	epnum = get_iface_desc(mixer->hostif)->bNumEndpoints;
> +	if (epnum == 0)
> +		return -EINVAL;
> +
>  	/* we need one interrupt input endpoint */
> -	if (get_iface_desc(mixer->hostif)->bNumEndpoints < 1)
> +	if (epnum < 1)
>  		return 0;

The change looks wrong.  We don't want to return an error here, as
mixer->urb is optional.  And the second check introduced above is
utterly nonsense; epnum is an unsigned int, so epnum < 1 means only
epnum == 0.

The problem is rather in the scarlett2 side, and it should have a
check there, not in the core function.


thanks,

Takashi

[PATCH v2] ALSA: scarlett2: Add the number of endpoints checked was 0

[Edward Adam Davis]

The user constructed a corrupted USB device, causing the USB device
enumeration phase to fail to resolve any endpoints. This resulted in
a null pointer dereference reported in [1] when the USB sound card
driver executed probe to initialize the mixer. 

To avoid the problem reported in [1], a check was added to ensure that
the number of endpoints contained in the interface was 0 when creating
mixer controls for the Focusrite Scarlett 2nd/3rd Gen USB sound card.

[1]
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
RIP: 0010:usb_endpoint_num include/uapi/linux/usb/ch9.h:479 [inline]
RIP: 0010:scarlett2_find_fc_interface sound/usb/mixer_scarlett2.c:8261 [inline]
RIP: 0010:scarlett2_init_private sound/usb/mixer_scarlett2.c:8295 [inline]
RIP: 0010:snd_scarlett2_controls_create sound/usb/mixer_scarlett2.c:8684 [inline]
RIP: 0010:snd_scarlett2_init.cold+0xbad/0x6c79 sound/usb/mixer_scarlett2.c:9407
Call Trace:
 snd_usb_mixer_apply_create_quirk+0x1c21/0x2b80 sound/usb/mixer_quirks.c:4446
 snd_usb_create_mixer+0x7a2/0x1910 sound/usb/mixer.c:3641
 usb_audio_probe+0xf6d/0x3a90 sound/usb/card.c:1033

Reported-by: syzbot+ae893a8901067fde2741@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ae893a8901067fde2741 
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
v1 -> v2: move the check to scarlett2

 sound/usb/mixer_scarlett2.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/sound/usb/mixer_scarlett2.c b/sound/usb/mixer_scarlett2.c
index ef3150581eab..4b300226f16c 100644
--- a/sound/usb/mixer_scarlett2.c
+++ b/sound/usb/mixer_scarlett2.c
@@ -9393,6 +9393,15 @@ int snd_scarlett2_init(struct usb_mixer_interface *mixer)
 		return 0;
 	}
 
+	if (get_iface_desc(mixer->hostif)->bNumEndpoints == 0) {
+		usb_audio_err(chip,
+			"%s: There are no endpoints for %04x:%04x\n",
+			__func__,
+			USB_ID_VENDOR(chip->usb_id),
+			USB_ID_PRODUCT(chip->usb_id));
+		return 0;
+	}
+
 	usb_audio_info(chip,
 		"Focusrite %s Mixer Driver enabled (pid=0x%04x); "
 		"report any issues to "
-- 
2.43.0

Re: [PATCH v2] ALSA: scarlett2: Add the number of endpoints checked was 0

[Takashi Iwai]

On Mon, 09 Mar 2026 10:57:03 +0100,
Edward Adam Davis wrote:
> 
> The user constructed a corrupted USB device, causing the USB device
> enumeration phase to fail to resolve any endpoints. This resulted in
> a null pointer dereference reported in [1] when the USB sound card
> driver executed probe to initialize the mixer. 
> 
> To avoid the problem reported in [1], a check was added to ensure that
> the number of endpoints contained in the interface was 0 when creating
> mixer controls for the Focusrite Scarlett 2nd/3rd Gen USB sound card.
> 
> [1]
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> RIP: 0010:usb_endpoint_num include/uapi/linux/usb/ch9.h:479 [inline]
> RIP: 0010:scarlett2_find_fc_interface sound/usb/mixer_scarlett2.c:8261 [inline]
> RIP: 0010:scarlett2_init_private sound/usb/mixer_scarlett2.c:8295 [inline]
> RIP: 0010:snd_scarlett2_controls_create sound/usb/mixer_scarlett2.c:8684 [inline]
> RIP: 0010:snd_scarlett2_init.cold+0xbad/0x6c79 sound/usb/mixer_scarlett2.c:9407
> Call Trace:
>  snd_usb_mixer_apply_create_quirk+0x1c21/0x2b80 sound/usb/mixer_quirks.c:4446
>  snd_usb_create_mixer+0x7a2/0x1910 sound/usb/mixer.c:3641
>  usb_audio_probe+0xf6d/0x3a90 sound/usb/card.c:1033
> 
> Reported-by: syzbot+ae893a8901067fde2741@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=ae893a8901067fde2741 
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
> v1 -> v2: move the check to scarlett2
> 
>  sound/usb/mixer_scarlett2.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/sound/usb/mixer_scarlett2.c b/sound/usb/mixer_scarlett2.c
> index ef3150581eab..4b300226f16c 100644
> --- a/sound/usb/mixer_scarlett2.c
> +++ b/sound/usb/mixer_scarlett2.c
> @@ -9393,6 +9393,15 @@ int snd_scarlett2_init(struct usb_mixer_interface *mixer)
>  		return 0;
>  	}
>  
> +	if (get_iface_desc(mixer->hostif)->bNumEndpoints == 0) {
> +		usb_audio_err(chip,
> +			"%s: There are no endpoints for %04x:%04x\n",
> +			__func__,
> +			USB_ID_VENDOR(chip->usb_id),
> +			USB_ID_PRODUCT(chip->usb_id));
> +		return 0;

This should be an error.  It's obviously a broken descriptor, and this
is the code specific to the certain configuration.


Takashi

Re: [PATCH v2] ALSA: scarlett2: Add the number of endpoints checked was 0

[Greg KH]

On Mon, Mar 09, 2026 at 05:57:03PM +0800, Edward Adam Davis wrote:
> The user constructed a corrupted USB device, causing the USB device
> enumeration phase to fail to resolve any endpoints. This resulted in
> a null pointer dereference reported in [1] when the USB sound card
> driver executed probe to initialize the mixer. 
> 
> To avoid the problem reported in [1], a check was added to ensure that
> the number of endpoints contained in the interface was 0 when creating
> mixer controls for the Focusrite Scarlett 2nd/3rd Gen USB sound card.
> 
> [1]
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> RIP: 0010:usb_endpoint_num include/uapi/linux/usb/ch9.h:479 [inline]
> RIP: 0010:scarlett2_find_fc_interface sound/usb/mixer_scarlett2.c:8261 [inline]
> RIP: 0010:scarlett2_init_private sound/usb/mixer_scarlett2.c:8295 [inline]
> RIP: 0010:snd_scarlett2_controls_create sound/usb/mixer_scarlett2.c:8684 [inline]
> RIP: 0010:snd_scarlett2_init.cold+0xbad/0x6c79 sound/usb/mixer_scarlett2.c:9407
> Call Trace:
>  snd_usb_mixer_apply_create_quirk+0x1c21/0x2b80 sound/usb/mixer_quirks.c:4446
>  snd_usb_create_mixer+0x7a2/0x1910 sound/usb/mixer.c:3641
>  usb_audio_probe+0xf6d/0x3a90 sound/usb/card.c:1033
> 
> Reported-by: syzbot+ae893a8901067fde2741@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=ae893a8901067fde2741 
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
> v1 -> v2: move the check to scarlett2
> 
>  sound/usb/mixer_scarlett2.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/sound/usb/mixer_scarlett2.c b/sound/usb/mixer_scarlett2.c
> index ef3150581eab..4b300226f16c 100644
> --- a/sound/usb/mixer_scarlett2.c
> +++ b/sound/usb/mixer_scarlett2.c
> @@ -9393,6 +9393,15 @@ int snd_scarlett2_init(struct usb_mixer_interface *mixer)
>  		return 0;
>  	}
>  
> +	if (get_iface_desc(mixer->hostif)->bNumEndpoints == 0) {
> +		usb_audio_err(chip,
> +			"%s: There are no endpoints for %04x:%04x\n",
> +			__func__,
> +			USB_ID_VENDOR(chip->usb_id),
> +			USB_ID_PRODUCT(chip->usb_id));
> +		return 0;
> +	}

Why not use the "normal" functions to check a USB device for the exact
specific types and numbers of endpoints instead of hand-coding it all?

thanks,

greg k-h

Re: [PATCH v2] ALSA: scarlett2: Add the number of endpoints checked was 0

[Takashi Iwai]

On Mon, 09 Mar 2026 11:03:46 +0100,
Takashi Iwai wrote:
> 
> On Mon, 09 Mar 2026 10:57:03 +0100,
> Edward Adam Davis wrote:
> > 
> > The user constructed a corrupted USB device, causing the USB device
> > enumeration phase to fail to resolve any endpoints. This resulted in
> > a null pointer dereference reported in [1] when the USB sound card
> > driver executed probe to initialize the mixer. 
> > 
> > To avoid the problem reported in [1], a check was added to ensure that
> > the number of endpoints contained in the interface was 0 when creating
> > mixer controls for the Focusrite Scarlett 2nd/3rd Gen USB sound card.
> > 
> > [1]
> > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> > RIP: 0010:usb_endpoint_num include/uapi/linux/usb/ch9.h:479 [inline]
> > RIP: 0010:scarlett2_find_fc_interface sound/usb/mixer_scarlett2.c:8261 [inline]
> > RIP: 0010:scarlett2_init_private sound/usb/mixer_scarlett2.c:8295 [inline]
> > RIP: 0010:snd_scarlett2_controls_create sound/usb/mixer_scarlett2.c:8684 [inline]
> > RIP: 0010:snd_scarlett2_init.cold+0xbad/0x6c79 sound/usb/mixer_scarlett2.c:9407
> > Call Trace:
> >  snd_usb_mixer_apply_create_quirk+0x1c21/0x2b80 sound/usb/mixer_quirks.c:4446
> >  snd_usb_create_mixer+0x7a2/0x1910 sound/usb/mixer.c:3641
> >  usb_audio_probe+0xf6d/0x3a90 sound/usb/card.c:1033
> > 
> > Reported-by: syzbot+ae893a8901067fde2741@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=ae893a8901067fde2741 
> > Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> > ---
> > v1 -> v2: move the check to scarlett2
> > 
> >  sound/usb/mixer_scarlett2.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/sound/usb/mixer_scarlett2.c b/sound/usb/mixer_scarlett2.c
> > index ef3150581eab..4b300226f16c 100644
> > --- a/sound/usb/mixer_scarlett2.c
> > +++ b/sound/usb/mixer_scarlett2.c
> > @@ -9393,6 +9393,15 @@ int snd_scarlett2_init(struct usb_mixer_interface *mixer)
> >  		return 0;
> >  	}
> >  
> > +	if (get_iface_desc(mixer->hostif)->bNumEndpoints == 0) {
> > +		usb_audio_err(chip,
> > +			"%s: There are no endpoints for %04x:%04x\n",
> > +			__func__,
> > +			USB_ID_VENDOR(chip->usb_id),
> > +			USB_ID_PRODUCT(chip->usb_id));
> > +		return 0;
> 
> This should be an error.  It's obviously a broken descriptor, and this
> is the code specific to the certain configuration.

... and that check alone doesn't cover all cases, I'm afraid.  The
scarlett2 driver code parses over multiple interfaces.

I guess rather a patch like below should cover better.


thanks,

Takashi

--- a/sound/usb/mixer_scarlett2.c
+++ b/sound/usb/mixer_scarlett2.c
@@ -8251,6 +8251,8 @@ static int scarlett2_find_fc_interface(struct usb_device *dev,
 
 		if (desc->bInterfaceClass != 255)
 			continue;
+		if (desc->bNumEndpoints < 1)
+			continue;
 
 		epd = get_endpoint(intf->altsetting, 0);
 		private->bInterfaceNumber = desc->bInterfaceNumber;