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a1c0b87b76
commit 0d0777ccaa2d46609d05b66ba0096802a2746193 upstream.
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.
Note: this changes the API for uhid devices when a request is made
through hid_hw_request. However, several considerations makes me think
this is fine:
- every request to a HID device made through hid_hw_request() would see
that change, but every request made through hid_hw_raw_request()
already has the new behaviour. So that means that the users are
already facing situations where they might have or not the first byte
being the null report ID when it is 0. We are making things more
straightforward in the end.
- uhid is mainly used for BLE devices
- uhid is also used for testing, but I don't see that change a big issue
- for BLE devices, we can check which kernel module is calling
hid_hw_request()
- and in those modules, we can check which are using a Bluetooth device
- and then we can check if the command is used with a report ID or not.
- surprise: none of the kernel module are using a report ID 0
- and finally, bluez, in its function set_report()[0], does the same
shift if the report ID is 0 and the given buffer has a size > 0.
[0] https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/profiles/input/hog-lib.c#n879
Reported-by: Alan Stern <stern@rowland.harvard.edu>
Closes: https://lore.kernel.org/linux-input/c75433e0-9b47-4072-bbe8-b1d14ea97b13@rowland.harvard.edu/
Reported-by: syzbot+8258d5439c49d4c35f43@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8258d5439c49d4c35f43
Tested-by: syzbot+8258d5439c49d4c35f43@syzkaller.appspotmail.com
Fixes: 4fa5a7f76c ("HID: core: implement generic .request()")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20250710-report-size-null-v2-2-ccf922b7c4e5@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
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