[alsa-devel] [PATCH] ALSA: usb-audio: Fix gpf in snd_usb_pipe_sanity_check

[Hillf Danton]

syzbot found the following crash on:

HEAD commit:    7f7867ff usb-fuzzer: main usb gadget fuzzer driver
git tree:       https://github.com/google/kasan.git usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=12befdc8600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=792eb47789f57810
dashboard link: https://syzkaller.appspot.com/bug?extid=d59c4387bfb6eced94e2
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16efc49fa00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13245854600000

usb 1-1: New USB device found, idVendor=07fd, idProduct=0004, bcdDevice=d5.ac
usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 1-1: config 0 descriptor??
usb 1-1: string descriptor 0 read error: -71
usb 1-1: Waiting for MOTU Microbook II to boot up...
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
CPU: 1 PID: 21 Comm: kworker/1:1 Not tainted 5.3.0-rc2+ #23
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: usb_hub_wq hub_event
RIP: 0010:snd_usb_pipe_sanity_check+0x80/0x130 sound/usb/helper.c:75
Code: 48 c1 ea 03 80 3c 02 00 0f 85 b3 00 00 00 48 8b 6d 00 c1 eb 1e 48 b8  
00 00 00 00 00 fc ff df 48 8d 7d 03 48 89 fa 48 c1 ea 03 <0f> b6 04 02 48  
89 fa 83 e2 07 38 d0 7f 04 84 c0 75 7b 48 b8 00 00
RSP: 0018:ffff8881da2f7010 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffffff8484d252
RDX: 0000000000000000 RSI: ffffffff8484d26c RDI: 0000000000000003
RBP: 0000000000000000 R08: ffff8881da22e000 R09: ffffed103b665d58
R10: ffffed103b665d57 R11: ffff8881db32eabf R12: 0000000000000000
R13: ffff8881d400ba80 R14: 1ffff1103b45ee06 R15: ffff8881c79244a0
FS:  0000000000000000(0000) GS:ffff8881db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f31b2a87000 CR3: 00000001d3fd4000 CR4: 00000000001406e0
Call Trace:
  snd_usb_motu_microbookii_communicate.constprop.0+0xa0/0x2fb  sound/usb/quirks.c:1007
  snd_usb_motu_microbookii_boot_quirk sound/usb/quirks.c:1051 [inline]
  snd_usb_apply_boot_quirk.cold+0x163/0x370 sound/usb/quirks.c:1280
  usb_audio_probe+0x2ec/0x2010 sound/usb/card.c:576
  usb_probe_interface+0x305/0x7a0 drivers/usb/core/driver.c:361
  really_probe+0x281/0x650 drivers/base/dd.c:548
  driver_probe_device+0x101/0x1b0 drivers/base/dd.c:709
  __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:816
  bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454
  __device_attach+0x217/0x360 drivers/base/dd.c:882
  bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514
  device_add+0xae6/0x16f0 drivers/base/core.c:2114
  usb_set_configuration+0xdf6/0x1670 drivers/usb/core/message.c:2023
  generic_probe+0x9d/0xd5 drivers/usb/core/generic.c:210
  usb_probe_device+0x99/0x100 drivers/usb/core/driver.c:266
  really_probe+0x281/0x650 drivers/base/dd.c:548
  driver_probe_device+0x101/0x1b0 drivers/base/dd.c:709
  __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:816
  bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454
  __device_attach+0x217/0x360 drivers/base/dd.c:882
  bus_probe_device+0x1e4/0x290 drivers/base/bus.c:514
  device_add+0xae6/0x16f0 drivers/base/core.c:2114
  usb_new_device.cold+0x6a4/0xe79 drivers/usb/core/hub.c:2536
  hub_port_connect drivers/usb/core/hub.c:5098 [inline]
  hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
  port_event drivers/usb/core/hub.c:5359 [inline]
  hub_event+0x1b5c/0x3640 drivers/usb/core/hub.c:5441
  process_one_work+0x92b/0x1530 kernel/workqueue.c:2269
  worker_thread+0x96/0xe20 kernel/workqueue.c:2415
  kthread+0x318/0x420 kernel/kthread.c:255
  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Modules linked in:
[ end trace 41e8577a8c48635e ]

It was introduced in commit 801ebf1043ae for checking pipe and endpoint
types. It is fixed by adding a check of the ep pointer in question.

Reported-by: syzbot <syzbot+d59c4387bfb6eced94e2 at syzkaller.appspotmail.com>
Fixes: commit 801ebf1043ae ("ALSA: usb-audio: Sanity checks for each pipe and EP types")
Cc: Andrey Konovalov <andreyknvl at google.com>
Signed-off-by: Hillf Danton <dhanton at sina.com>
---
This is to make syzbot happy for now and in long run we can make
snd_usb_pipe_sanity_check() available outside sound/usb by making
usb_urb_ep_type_check() a wrapper of the former. We will revisit
sound/usb once when things in the usb/core get in place.

 sound/usb/helper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/helper.c b/sound/usb/helper.c
index 71d5f54..4c12cc5 100644
--- a/sound/usb/helper.c
+++ b/sound/usb/helper.c
@@ -72,7 +72,7 @@ int snd_usb_pipe_sanity_check(struct usb_device *dev, unsigned int pipe)
 	struct usb_host_endpoint *ep;
 
 	ep = usb_pipe_endpoint(dev, pipe);
-	if (usb_pipetype(pipe) != pipetypes[usb_endpoint_type(&ep->desc)])
+	if (!ep || usb_pipetype(pipe) != pipetypes[usb_endpoint_type(&ep->desc)])
 		return -EINVAL;
 	return 0;
 }
--