KMSAN: kernel-infoleak in raw_ioctl

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ce8056d1 wip: changed copy_from_user where instrumented
git tree: https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=141eb8b2900000
kernel config: https://syzkaller.appspot.com/x/.config?x=3afe005fb99591f
dashboard link: https://syzkaller.appspot.com/bug?extid=a7e220df5a81d1ab400e
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a7e220...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak in kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:253
CPU: 0 PID: 22259 Comm: syz-executor.5 Not tainted 5.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x21c/0x280 lib/dump_stack.c:118
kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
kmsan_internal_check_memory+0x238/0x3d0 mm/kmsan/kmsan.c:423
kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:253
instrument_copy_to_user include/linux/instrumented.h:91 [inline]
_copy_to_user+0x18e/0x260 lib/usercopy.c:39
copy_to_user include/linux/uaccess.h:186 [inline]
raw_ioctl_event_fetch drivers/usb/gadget/legacy/raw_gadget.c:567 [inline]
raw_ioctl+0x4995/0x5810 drivers/usb/gadget/legacy/raw_gadget.c:1213
__do_compat_sys_ioctl fs/ioctl.c:847 [inline]
__se_compat_sys_ioctl+0x55f/0x1100 fs/ioctl.c:798
__ia32_compat_sys_ioctl+0x4a/0x70 fs/ioctl.c:798
do_syscall_32_irqs_on arch/x86/entry/common.c:430 [inline]
__do_fast_syscall_32+0x2af/0x480 arch/x86/entry/common.c:477
do_fast_syscall_32+0x6b/0xd0 arch/x86/entry/common.c:505
do_SYSENTER_32+0x73/0x90 arch/x86/entry/common.c:554
entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7fbd549
Code: Bad RIP value.
RSP: 002b:00000000f55b5058 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000080085502
RDX: 00000000f55b60ac RSI: 000000000002acf0 RDI: 0000000000000003
RBP: 00000000f55b7228 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
kmsan_internal_chain_origin+0xad/0x130 mm/kmsan/kmsan.c:310
kmsan_memcpy_memmove_metadata+0x272/0x2e0 mm/kmsan/kmsan.c:247
kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:267
__msan_memcpy+0x43/0x50 mm/kmsan/kmsan_instr.c:116
raw_event_queue_add drivers/usb/gadget/legacy/raw_gadget.c:74 [inline]
raw_queue_event+0x2b3/0x5c0 drivers/usb/gadget/legacy/raw_gadget.c:225
gadget_setup+0x48c/0x530 drivers/usb/gadget/legacy/raw_gadget.c:343
dummy_timer+0x2c4d/0x71c0 drivers/usb/gadget/udc/dummy_hcd.c:1899
call_timer_fn+0x226/0x550 kernel/time/timer.c:1404
expire_timers+0x4fc/0x780 kernel/time/timer.c:1449
__run_timers+0xaf4/0xd30 kernel/time/timer.c:1773
run_timer_softirq+0x2d/0x50 kernel/time/timer.c:1786
__do_softirq+0x2ea/0x7f5 kernel/softirq.c:293

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
kmsan_internal_chain_origin+0xad/0x130 mm/kmsan/kmsan.c:310
__msan_chain_origin+0x50/0x90 mm/kmsan/kmsan_instr.c:165
dummy_timer+0x1d82/0x71c0 drivers/usb/gadget/udc/dummy_hcd.c:1867
call_timer_fn+0x226/0x550 kernel/time/timer.c:1404
expire_timers+0x4fc/0x780 kernel/time/timer.c:1449
__run_timers+0xaf4/0xd30 kernel/time/timer.c:1773
run_timer_softirq+0x2d/0x50 kernel/time/timer.c:1786
__do_softirq+0x2ea/0x7f5 kernel/softirq.c:293

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
kmsan_internal_chain_origin+0xad/0x130 mm/kmsan/kmsan.c:310
__msan_chain_origin+0x50/0x90 mm/kmsan/kmsan_instr.c:165
usb_control_msg+0x5df/0x820 drivers/usb/core/message.c:149
__usbnet_write_cmd drivers/net/usb/usbnet.c:2035 [inline]
usbnet_write_cmd+0x3de/0x480 drivers/net/usb/usbnet.c:2073
asix_write_cmd+0x18b/0x2c0 drivers/net/usb/asix_common.c:48
ax88772_hw_reset+0x1bd/0xc30 drivers/net/usb/asix_devices.c:361
ax88772_bind+0x8f3/0x1400 drivers/net/usb/asix_devices.c:730
usbnet_probe+0x1152/0x3f90 drivers/net/usb/usbnet.c:1737
usb_probe_interface+0xece/0x1550 drivers/usb/core/driver.c:374
really_probe+0xf20/0x20b0 drivers/base/dd.c:529
driver_probe_device+0x293/0x390 drivers/base/dd.c:701
__device_attach_driver+0x63f/0x830 drivers/base/dd.c:807
bus_for_each_drv+0x2ca/0x3f0 drivers/base/bus.c:431
__device_attach+0x4e2/0x7f0 drivers/base/dd.c:873
device_initial_probe+0x4a/0x60 drivers/base/dd.c:920
bus_probe_device+0x177/0x3d0 drivers/base/bus.c:491
device_add+0x3b0e/0x40d0 drivers/base/core.c:2680
usb_set_configuration+0x380f/0x3f10 drivers/usb/core/message.c:2032
usb_generic_driver_probe+0x138/0x300 drivers/usb/core/generic.c:241
usb_probe_device+0x311/0x490 drivers/usb/core/driver.c:272
really_probe+0xf20/0x20b0 drivers/base/dd.c:529
driver_probe_device+0x293/0x390 drivers/base/dd.c:701
__device_attach_driver+0x63f/0x830 drivers/base/dd.c:807
bus_for_each_drv+0x2ca/0x3f0 drivers/base/bus.c:431
__device_attach+0x4e2/0x7f0 drivers/base/dd.c:873
device_initial_probe+0x4a/0x60 drivers/base/dd.c:920
bus_probe_device+0x177/0x3d0 drivers/base/bus.c:491
device_add+0x3b0e/0x40d0 drivers/base/core.c:2680
usb_new_device+0x1bd4/0x2a30 drivers/usb/core/hub.c:2554
hub_port_connect drivers/usb/core/hub.c:5208 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5348 [inline]
port_event drivers/usb/core/hub.c:5494 [inline]
hub_event+0x5e7b/0x8a70 drivers/usb/core/hub.c:5576
process_one_work+0x1688/0x2140 kernel/workqueue.c:2269
worker_thread+0x10bc/0x2730 kernel/workqueue.c:2415
kthread+0x551/0x590 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
kmsan_internal_chain_origin+0xad/0x130 mm/kmsan/kmsan.c:310
__msan_chain_origin+0x50/0x90 mm/kmsan/kmsan_instr.c:165
ax88772_bind+0x82e/0x1400 drivers/net/usb/asix_devices.c:720
usbnet_probe+0x1152/0x3f90 drivers/net/usb/usbnet.c:1737
usb_probe_interface+0xece/0x1550 drivers/usb/core/driver.c:374
really_probe+0xf20/0x20b0 drivers/base/dd.c:529
driver_probe_device+0x293/0x390 drivers/base/dd.c:701
__device_attach_driver+0x63f/0x830 drivers/base/dd.c:807
bus_for_each_drv+0x2ca/0x3f0 drivers/base/bus.c:431
__device_attach+0x4e2/0x7f0 drivers/base/dd.c:873
device_initial_probe+0x4a/0x60 drivers/base/dd.c:920
bus_probe_device+0x177/0x3d0 drivers/base/bus.c:491
device_add+0x3b0e/0x40d0 drivers/base/core.c:2680
usb_set_configuration+0x380f/0x3f10 drivers/usb/core/message.c:2032
usb_generic_driver_probe+0x138/0x300 drivers/usb/core/generic.c:241
usb_probe_device+0x311/0x490 drivers/usb/core/driver.c:272
really_probe+0xf20/0x20b0 drivers/base/dd.c:529
driver_probe_device+0x293/0x390 drivers/base/dd.c:701
__device_attach_driver+0x63f/0x830 drivers/base/dd.c:807
bus_for_each_drv+0x2ca/0x3f0 drivers/base/bus.c:431
__device_attach+0x4e2/0x7f0 drivers/base/dd.c:873
device_initial_probe+0x4a/0x60 drivers/base/dd.c:920
bus_probe_device+0x177/0x3d0 drivers/base/bus.c:491
device_add+0x3b0e/0x40d0 drivers/base/core.c:2680
usb_new_device+0x1bd4/0x2a30 drivers/usb/core/hub.c:2554
hub_port_connect drivers/usb/core/hub.c:5208 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5348 [inline]
port_event drivers/usb/core/hub.c:5494 [inline]
hub_event+0x5e7b/0x8a70 drivers/usb/core/hub.c:5576
process_one_work+0x1688/0x2140 kernel/workqueue.c:2269
worker_thread+0x10bc/0x2730 kernel/workqueue.c:2415
kthread+0x551/0x590 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293

Local variable ----buf.i@asix_get_phy_addr created at:
asix_read_cmd drivers/net/usb/asix_common.c:312 [inline]
asix_read_phy_addr drivers/net/usb/asix_common.c:295 [inline]
asix_get_phy_addr+0x4d/0x290 drivers/net/usb/asix_common.c:314
asix_read_cmd drivers/net/usb/asix_common.c:312 [inline]
asix_read_phy_addr drivers/net/usb/asix_common.c:295 [inline]
asix_get_phy_addr+0x4d/0x290 drivers/net/usb/asix_common.c:314

Byte 10 of 16 is uninitialized
Memory access of size 16 starts at ffff88810839b4d0
Data copied to user address 00000000f55b60ac
=====================================================


---
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[Greg KH]

On Sun, Aug 09, 2020 at 09:27:18AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: ce8056d1 wip: changed copy_from_user where instrumented
> git tree: https://github.com/google/kmsan.git master
> console output: https://syzkaller.appspot.com/x/log.txt?x=141eb8b2900000
> kernel config: https://syzkaller.appspot.com/x/.config?x=3afe005fb99591f
> dashboard link: https://syzkaller.appspot.com/bug?extid=a7e220df5a81d1ab400e
> compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> userspace arch: i386
>
> Unfortunately, I don't have any reproducer for this issue yet.

The irony of a kernel module written for syzbot testing, causing syzbot
reports....

[Dmitry Vyukov]

The raw gadget and KCOV are also kernel code and subject to all the
same rules as any other kernel code from syzkaller point of view.

But I think the root cause of this bug is the origin of the uninitialized-ness:

[Greg KH]

read buffers sent to USB hardware are ment to be filled in by the
hardware with the data received from it, we do not zero-out those
buffers before passing the pointer there.

Perhaps with testing frameworks like the raw usb controller, that might
cause a number of false-positives to happen?

thanks,

greg k-h

[Greg KH]

Ah, wait, that buffer is coming from the stack, which isn't allowed in
the first place :(

So that should be changed anyway to a dynamic allocation, I'll go write
up a patch...

thanks,

greg k-h

[Greg KH]

Nope, my fault, the data is not coming from the stack, so all is good.

thanks,

greg k-h

[Dmitry Vyukov]

My reading of the code is that asix_read_cmd returns the number of
bytes actually read, which may be less than requested.
This happens in __usbnet_read_cmd:
https://elixir.bootlin.com/linux/latest/source/drivers/net/usb/usbnet.c#L2002
So this code in asix_read_phy_addr will need produce an uninit value
for result if <2 bytes read:

u8 buf[2];
int ret = asix_read_cmd(dev, AX_CMD_READ_PHY_ID, 0, 0, 2, buf, 0);
if (ret < 0)
netdev_err(dev->net, "Error reading PHYID register: %02x\n", ret);
ret = buf[offset];
return ret;

And it looks like all of 13 uses of asix_read_cmd in
drivers/net/usb/asix_common.c are subject to this bug as well.

[Greg KH]

Ah, yeah, and no one checks error values either, there's even a TODO
statement in the driver about that :(

Good catch, I'll point some interns at this and see if they can fix it
up, thanks!

greg k-h

[Andrey Konovalov]

Yeah, such issues are unfortunately currently getting attributed to
raw-gadget. I wonder if we can improve crash parsing code to cover
this kind of cases... We would need to skip the first few
raw-gadget/USB-related stack traces, and only take one of the "Uninit
was stored to memory at" ones.

[Dmitry Vyukov]

Looking at some other reports in the past I considered if we should
attribute uninit's to the _origin_ stack rather than all places the
origin may end up being used. But I don't have quantitative data on if
it will improve quality overall or not. There are definitely cases
where it will be wrong as well -- in particular allocation of skb's in
sendmsg.

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: ce8056d1 wip: changed copy_from_user where instrumented
git tree: https://github.com/google/kmsan.git master

console output: https://syzkaller.appspot.com/x/log.txt?x=12a834ee900000

kernel config: https://syzkaller.appspot.com/x/.config?x=3afe005fb99591f
dashboard link: https://syzkaller.appspot.com/bug?extid=a7e220df5a81d1ab400e
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=133bd37a900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=133175a6900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a7e220...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak in kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:253

CPU: 1 PID: 8488 Comm: syz-executor009 Not tainted 5.8.0-rc5-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x21c/0x280 lib/dump_stack.c:118
kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
kmsan_internal_check_memory+0x238/0x3d0 mm/kmsan/kmsan.c:423
kmsan_copy_to_user+0x81/0x90 mm/kmsan/kmsan_hooks.c:253
instrument_copy_to_user include/linux/instrumented.h:91 [inline]
_copy_to_user+0x18e/0x260 lib/usercopy.c:39
copy_to_user include/linux/uaccess.h:186 [inline]
raw_ioctl_event_fetch drivers/usb/gadget/legacy/raw_gadget.c:567 [inline]
raw_ioctl+0x4995/0x5810 drivers/usb/gadget/legacy/raw_gadget.c:1213

vfs_ioctl fs/ioctl.c:48 [inline]
ksys_ioctl fs/ioctl.c:753 [inline]
__do_sys_ioctl fs/ioctl.c:762 [inline]
__se_sys_ioctl+0x319/0x4d0 fs/ioctl.c:760
__x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:760
do_syscall_64+0xad/0x160 arch/x86/entry/common.c:386
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x444cf7
Code: Bad RIP value.
RSP: 002b:00007fff38034848 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000444cf7
RDX: 00007fff38035870 RSI: 0000000080085502 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000019
R10: 0000000000000075 R11: 0000000000000246 R12: 00000000004029f0
R13: 0000000000402a80 R14: 0000000000000000 R15: 0000000000000000

Memory access of size 16 starts at ffff8881051954d0
Data copied to user address 00007fff38035870
=====================================================

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+a7e220...@syzkaller.appspotmail.com

Tested on:

commit: ce8056d1 wip: changed copy_from_user where instrumented
git tree: https://github.com/google/kmsan.git master

kernel config: https://syzkaller.appspot.com/x/.config?x=3afe005fb99591f
dashboard link: https://syzkaller.appspot.com/bug?extid=a7e220df5a81d1ab400e
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

patch: https://syzkaller.appspot.com/x/patch.diff?x=17c01a96900000

Note: testing is done by a robot and is best-effort only.

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+a7e220...@syzkaller.appspotmail.com

Tested on:

commit: ce8056d1 wip: changed copy_from_user where instrumented
git tree: https://github.com/google/kmsan.git master
kernel config: https://syzkaller.appspot.com/x/.config?x=3afe005fb99591f
dashboard link: https://syzkaller.appspot.com/bug?extid=a7e220df5a81d1ab400e
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

patch: https://syzkaller.appspot.com/x/patch.diff?x=14a9a7ee900000