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

[Sean Young]

On Wed, Jan 13, 2021 at 07:11:22PM +0800, Dongliang Mu wrote:
> 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 <mudongliangabcd@xxxxxxxxx>
> ---
>  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;

I'm not sure this is correct. This checks the second byte for *any* response,
not just MCE_RSP_EQIRCFS response which is causing the "shift out of bounds"
issue.

I think the check belongs within the MCE_RSP_EQIRCFS case.

Lastly it should have been break, not continue.

Thanks

Sean



>  			mceusb_dev_printdata(ir, ir->buf_in, buf_len, i - 1,
>  					     ir->rem + 2, false);
>  			if (i + ir->rem < buf_len)
> -- 
> 2.25.1