linux-kernel - Re: KASAN: global-out-of-bounds Read in qmi_wwan

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Date:   Mon, 24 Jun 2019 14:59:11 +0200
From:   Bjørn Mork <bjorn@...k.no>
To:     Kristian Evensen <kristian.evensen@...il.com>
Cc:     syzbot <syzbot+b68605d7fadd21510de1@...kaller.appspotmail.com>,
        andreyknvl@...gle.com, davem@...emloft.net,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: global-out-of-bounds Read in qmi_wwan_probe

syzbot <syzbot+b68605d7fadd21510de1@...kaller.appspotmail.com> writes:

> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    9939f56e 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=1615a669a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=df134eda130bb43a
> dashboard link: https://syzkaller.appspot.com/bug?extid=b68605d7fadd21510de1
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10630af6a00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1127da69a00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+b68605d7fadd21510de1@...kaller.appspotmail.com
>
> usb 1-1: new high-speed USB device number 2 using dummy_hcd
> usb 1-1: Using ep0 maxpacket: 8
> usb 1-1: New USB device found, idVendor=12d1, idProduct=14f1,
> bcdDevice=d4.d9
> usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
> usb 1-1: config 0 descriptor??
> ==================================================================
> BUG: KASAN: global-out-of-bounds in qmi_wwan_probe+0x342/0x360
> drivers/net/usb/qmi_wwan.c:1417
> Read of size 8 at addr ffffffff8618c140 by task kworker/1:1/22
>
> CPU: 1 PID: 22 Comm: kworker/1:1 Not tainted 5.2.0-rc5+ #11
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011
> Workqueue: usb_hub_wq hub_event
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0xca/0x13e lib/dump_stack.c:113
>  print_address_description+0x67/0x231 mm/kasan/report.c:188
>  __kasan_report.cold+0x1a/0x32 mm/kasan/report.c:317
>  kasan_report+0xe/0x20 mm/kasan/common.c:614
>  qmi_wwan_probe+0x342/0x360 drivers/net/usb/qmi_wwan.c:1417
>  usb_probe_interface+0x305/0x7a0 drivers/usb/core/driver.c:361
>  really_probe+0x281/0x660 drivers/base/dd.c:509
>  driver_probe_device+0x104/0x210 drivers/base/dd.c:670
>  __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:777
>  bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454
>

Hello Kristian!

I need some help understanding this...  IIUC syzbot is claiming an
out-of-bounds access at line 1417 in v5.2-rc5.  Or whatever - I'm having
a hard time deciphering what kernel version the bot is actually
testing. The claimed HEAD is not a kernel commit.  At least not in my
kernel...


But if this is correct, then it points to the info->data access you
recently added:

822e44b45eb99 (Kristian Evensen        2019-03-02 13:32:26 +0100 1409)  /* Several Quectel modems supports dynamic interface configuration, so
7c5cca3588545 (Kristian Evensen        2018-09-08 13:50:48 +0200 1410)   * we need to match on class/subclass/protocol. These values are
7c5cca3588545 (Kristian Evensen        2018-09-08 13:50:48 +0200 1411)   * identical for the diagnostic- and QMI-interface, but bNumEndpoints is
7c5cca3588545 (Kristian Evensen        2018-09-08 13:50:48 +0200 1412)   * different. Ignore the current interface if the number of endpoints
e4bf63482c309 (Kristian Evensen        2019-04-07 15:39:09 +0200 1413)   * equals the number for the diag interface (two).
7c5cca3588545 (Kristian Evensen        2018-09-08 13:50:48 +0200 1414)   */
e4bf63482c309 (Kristian Evensen        2019-04-07 15:39:09 +0200 1415)  info = (void *)&id->driver_info;
e4bf63482c309 (Kristian Evensen        2019-04-07 15:39:09 +0200 1416) 
e4bf63482c309 (Kristian Evensen        2019-04-07 15:39:09 +0200 1417)  if (info->data & QMI_WWAN_QUIRK_QUECTEL_DYNCFG) {
e4bf63482c309 (Kristian Evensen        2019-04-07 15:39:09 +0200 1418)          if (desc->bNumEndpoints == 2)
e4bf63482c309 (Kristian Evensen        2019-04-07 15:39:09 +0200 1419)                  return -ENODEV;
e4bf63482c309 (Kristian Evensen        2019-04-07 15:39:09 +0200 1420)  }


I must be blind. I cannot see how this could end up failing.
id->driver_info is always set to one of qmi_wwan_info,
qmi_wwan_info_quirk_dtr or qmi_wwan_info_quirk_quectel_dyncfg at this
point.  How does that end up out-of-bounds?



Bjørn