[PATCH] Fix shift-out-of-bound in mceusb_process_ir_data

[Dongliang Mu]

The missing check of ir->buf_in[i+1] can lead to an shift-out-of-bound
in mceusb_handle_command or mceusb_dev_printdata. This patch adds a
check to limit its value lower than 16. The concrete report of UBSAN is
as follows.

UBSAN: shift-out-of-bounds in drivers/media/rc/mceusb.c:704:13
shift exponent 230 is too large for 32-bit type 'unsigned int'
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.10.0-syzkaller #0
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
 __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:395
 mceusb_dev_printdata.cold+0x19/0x1e drivers/media/rc/mceusb.c:704
 mceusb_process_ir_data drivers/media/rc/mceusb.c:1275 [inline]
 mceusb_dev_recv+0x3cb/0x1990 drivers/media/rc/mceusb.c:1376
 __usb_hcd_giveback_urb+0x2b0/0x5c0 drivers/usb/core/hcd.c:1657
 usb_hcd_giveback_urb+0x38c/0x430 drivers/usb/core/hcd.c:1728
 dummy_timer+0x11f4/0x32a0 drivers/usb/gadget/udc/dummy_hcd.c:1971

Signed-off-by: Dongliang Mu <mudonglianga...@gmail.com>
---
 drivers/media/rc/mceusb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/media/rc/mceusb.c b/drivers/media/rc/mceusb.c
index f9616158bcf4..755808c6e747 100644
--- a/drivers/media/rc/mceusb.c
+++ b/drivers/media/rc/mceusb.c
@@ -1272,6 +1272,8 @@ static void mceusb_process_ir_data(struct mceusb_dev *ir, 
int buf_len)
                switch (ir->parser_state) {
                case SUBCMD:
                        ir->rem = mceusb_cmd_datasize(ir->cmd, ir->buf_in[i]);
+                       if (ir->buf_in[i+1] >= 16)
+                               continue;
                        mceusb_dev_printdata(ir, ir->buf_in, buf_len, i - 1,
                                             ir->rem + 2, false);
                        if (i + ir->rem < buf_len)
-- 
2.25.1