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SubjectRe: "UBSAN: shift-out-of-bounds in mceusb_dev_recv" should share the same root cause with "UBSAN: shift-out-of-bounds in mceusb_dev_printdata"
On Wed, Jan 13, 2021 at 3:51 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Wed, Jan 13, 2021 at 01:04:44PM +0800, 慕冬亮 wrote:
> > Hi developers,
> >
> > I found that "UBSAN: shift-out-of-bounds in mceusb_dev_recv" and
> > "UBSAN: shift-out-of-bounds in mceusb_dev_printdata" should share the
> > same root cause.
> > The reason is that the PoCs after minimization has a high similarity
> > with the other. And their stack trace only diverges at the last
> > function call. The following is some analysis for this bug.
> >
> > The following code in the mceusb_process_ir_data is the vulnerable
> > --------------------------------------------------------------------------------------------------------------------------
> > for (; i < buf_len; i++) {
> > switch (ir->parser_state) {
> > case SUBCMD:
> > ir->rem = mceusb_cmd_datasize(ir->cmd, ir->buf_in[i]);
> > mceusb_dev_printdata(ir, ir->buf_in, buf_len, i - 1,
> > ir->rem + 2, false);
> > if (i + ir->rem < buf_len)
> > mceusb_handle_command(ir, &ir->buf_in[i - 1]);
> > --------------------------------------------------------------------------------------------------------------------------
> >
> > The first report crashes at a shift operation(1<<*hi) in mceusb_handle_command.
> > --------------------------------------------------------------------------------------------------------------------------
> > static void mceusb_handle_command(struct mceusb_dev *ir, u8 *buf_in)
> > {
> > u8 *hi = &buf_in[2]; /* read only when required */
> > if (cmd == MCE_CMD_PORT_SYS) {
> > switch (subcmd) {
> > case MCE_RSP_GETPORTSTATUS:
> > if (buf_in[5] == 0)
> > ir->txports_cabled |= 1 << *hi;
> > --------------------------------------------------------------------------------------------------------------------------
> >
> > The second report crashes at another shift operation (1U << data[0])
> > in mceusb_dev_printdata.
> > --------------------------------------------------------------------------------------------------------------------------
> > static void mceusb_dev_printdata(struct mceusb_dev *ir, u8 *buf, int buf_len,
> > int offset, int len, bool out)
> > {
> > data = &buf[offset] + 2;
> >
> > period = DIV_ROUND_CLOSEST((1U << data[0] * 2) *
> > (data[1] + 1), 10);
> > --------------------------------------------------------------------------------------------------------------------------
> >
> > >From the analysis, we can know the data[0] and *hi access the same
> > memory cell - ``ir->buf_in[i+1]``. So the root cause should be that it
> > misses the check of ir->buf_in[i+1].
> >
> > For the patch of this bug, there is one from anant.thazhemadam@gmail.com:
> > --------------------------------------------------------------------------------------------------------------------------
> > diff --git a/drivers/media/rc/mceusb.c b/drivers/media/rc/mceusb.c
> > index f1dbd059ed08..79de721b1c4a 100644
> > --- a/drivers/media/rc/mceusb.c
> > +++ b/drivers/media/rc/mceusb.c
> > @@ -1169,7 +1169,7 @@ static void mceusb_handle_command(struct
> > mceusb_dev *ir, u8 *buf_in)
> > switch (subcmd) {
> > /* the one and only 5-byte return value command */
> > case MCE_RSP_GETPORTSTATUS:
> > - if (buf_in[5] == 0)
> > + if ((buf_in[5] == 0) && (*hi <= 32))
> > ir->txports_cabled |= 1 << *hi;
> > break;
> > --------------------------------------------------------------------------------------------------------------------------
> > I tried this patch in the second crash report and found it does not
> > work. I think we should add another filter for the value in
> > ``ir->buf_in[i+1]``.
> >
> > With this grouping, I think developers can take into consideration the
> > issue in mceusb_dev_printdata and generate a complete patch for this
> > bug.
>
> Why not create a patch yourself and submit it? That way you get the
> correct credit for solving the problem.
>

I have sent a simple but working patch to the corresponding
developers. We can take it as a base to discuss.

And this email is to provide some information about bug duplication
for developers as I am doing some research on crash deduplication. I
want to get some credits if our grouping information is useful for
some kernel developers.

> thanks,
>
> greg k-h

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