The low level transport driver expects the first byte to be the report ID, even when the report ID is not use (in which case they just shift the buffer).

However, __hid_request() whas not offsetting the buffer it used by one in this case, meaning that the raw_request() callback emitted by the transport driver would be stripped of the first byte.

Reported-by: Alan Stern stern@rowland.harvard.edu Closes: https://lore.kernel.org/linux-input/c75433e0-9b47-4072-bbe8-b1d14ea97b13@row... Reported-by: syzbot+8258d5439c49d4c35f43@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=8258d5439c49d4c35f43 Tested-by: syzbot+8258d5439c49d4c35f43@syzkaller.appspotmail.com Fixes: 4fa5a7f76cc7 ("HID: core: implement generic .request()") Cc: stable@vger.kernel.org Signed-off-by: Benjamin Tissoires bentiss@kernel.org --- drivers/hid/hid-core.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c index 1a231dd9e4bc83202f2cbcd8b3a21e8c82b9deec..320887c365f7a36f7376556ffd19f99e52b7d732 100644 --- a/drivers/hid/hid-core.c +++ b/drivers/hid/hid-core.c @@ -1976,7 +1976,7 @@ static struct hid_report *hid_get_report(struct hid_report_enum *report_enum, int __hid_request(struct hid_device *hid, struct hid_report *report, enum hid_class_request reqtype) { - char *buf; + char *buf, *data_buf; int ret; u32 len;

@@ -1984,10 +1984,17 @@ int __hid_request(struct hid_device *hid, struct hid_report *report, if (!buf) return -ENOMEM;

+ data_buf = buf; len = hid_report_len(report);

+ if (report->id == 0) { + /* reserve the first byte for the report ID */ + data_buf++; + len++; + } + if (reqtype == HID_REQ_SET_REPORT) - hid_output_report(report, buf); + hid_output_report(report, data_buf);

ret = hid->ll_driver->raw_request(hid, report->id, buf, len, report->type, reqtype);

Syzbot found a buffer underflow in __hid_request(). Add a related test case for it.

It's not perfect, but it allows to catch a corner case when a report descriptor is crafted so that it has a size of 0.

Signed-off-by: Benjamin Tissoires bentiss@kernel.org --- tools/testing/selftests/hid/tests/test_mouse.py | 70 +++++++++++++++++++++++++ 1 file changed, 70 insertions(+)

diff --git a/tools/testing/selftests/hid/tests/test_mouse.py b/tools/testing/selftests/hid/tests/test_mouse.py index 66daf7e5975ca50f0b065080669d7f6123fb177f..eb4e15a0e53bd5f3c8e0ea02365ff9da7eead93d 100644 --- a/tools/testing/selftests/hid/tests/test_mouse.py +++ b/tools/testing/selftests/hid/tests/test_mouse.py @@ -439,6 +439,68 @@ class BadResolutionMultiplierMouse(ResolutionMultiplierMouse): return 32 # EPIPE

+class BadReportDescriptorMouse(BaseMouse): + """ + This "device" was one autogenerated by syzbot. There are a lot of issues in + it, and the most problematic is that it declares features that have no + size. + + This leads to report->size being set to 0 and can mess up with usbhid + internals. Fortunately, uhid merely passes the incoming buffer, without + touching it so a buffer of size 0 will be translated to [] without + triggering a kernel oops. + + Because the report descriptor is wrong, no input are created, and we need + to tweak a little bit the parameters to make it look correct. + """ + + # fmt: off + report_descriptor = [ + 0x96, 0x01, 0x00, # Report Count (1) 0 + 0x06, 0x01, 0x00, # Usage Page (Generic Desktop) 3 + # 0x03, 0x00, 0x00, 0x00, 0x00, # Ignored by the kernel somehow + 0x2a, 0x90, 0xa0, # Usage Maximum (41104) 6 + 0x27, 0x00, 0x00, 0x00, 0x00, # Logical Maximum (0) 9 + 0xb3, 0x81, 0x3e, 0x25, 0x03, # Feature (Cnst,Arr,Abs,Vol) 14 + 0x1b, 0xdd, 0xe8, 0x40, 0x50, # Usage Minimum (1346431197) 19 + 0x3b, 0x5d, 0x8c, 0x3d, 0xda, # Designator Index 24 + ] + # fmt: on + + def __init__( + self, rdesc=report_descriptor, name=None, input_info=(3, 0x045E, 0x07DA) + ): + super().__init__(rdesc, name, input_info) + self.high_resolution_report_called = False + + def get_evdev(self, application=None): + assert self._input_nodes is None + return ( + "Ok" # should be a list or None, but both would fail, so abusing the system + ) + + def next_sync_events(self, application=None): + # there are no evdev nodes, so no events + return [] + + def is_ready(self): + # we wait for the SET_REPORT command to come + return self.high_resolution_report_called + + def set_report(self, req, rnum, rtype, data): + if rtype != self.UHID_FEATURE_REPORT: + raise InvalidHIDCommunication(f"Unexpected report type: {rtype}") + if rnum != 0x0: + raise InvalidHIDCommunication(f"Unexpected report number: {rnum}") + + if len(data) != 1: + raise InvalidHIDCommunication(f"Unexpected data: {data}, expected '[0]'") + + self.high_resolution_report_called = True + + return 0 + + class ResolutionMultiplierHWheelMouse(TwoWheelMouse): # fmt: off report_descriptor = [ @@ -975,3 +1037,11 @@ class TestMiMouse(TestWheelMouse): # assert below print out the real error pass assert remaining == [] + + +class TestBadReportDescriptorMouse(base.BaseTestCase.TestUhid): + def create_device(self): + return BadReportDescriptorMouse() + + def assertName(self, uhdev): + pass