Re: [PATCH next] tee: qcom: prevent potential off by one read

[Dan Carpenter <dan.carpenter@linaro.org>]

On Wed, Sep 24, 2025 at 11:21:34AM +0200, Jens Wiklander wrote:
> On Wed, Sep 24, 2025 at 9:36 AM Dan Carpenter <dan.carpenter@linaro.org> wrote:
> >
> > On Wed, Sep 24, 2025 at 08:58:45AM +1000, Amirreza Zarrabi wrote:
> > >
> > >
> > > On 9/24/2025 8:48 AM, Amirreza Zarrabi wrote:
> > > > On 9/18/2025 7:50 PM, Dan Carpenter wrote:
> > > >> Re-order these checks to check if "i" is a valid array index before using
> > > >> it.  This prevents a potential off by one read access.
> > > >>
> > > >> Fixes: d6e290837e50 ("tee: add Qualcomm TEE driver")
> > > >> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> > > >> ---
> > > >>  drivers/tee/qcomtee/call.c | 2 +-
> > > >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >>
> > > >> diff --git a/drivers/tee/qcomtee/call.c b/drivers/tee/qcomtee/call.c
> > > >> index cc17a48d0ab7..ac134452cc9c 100644
> > > >> --- a/drivers/tee/qcomtee/call.c
> > > >> +++ b/drivers/tee/qcomtee/call.c
> > > >> @@ -308,7 +308,7 @@ static int qcomtee_params_from_args(struct tee_param *params,
> > > >>    }
> > > >>
> > > >>    /* Release any IO and OO objects not processed. */
> > > >> -  for (; u[i].type && i < num_params; i++) {
> > > >> +  for (; i < num_params && u[i].type; i++) {
> > > >>            if (u[i].type == QCOMTEE_ARG_TYPE_OO ||
> > > >>                u[i].type == QCOMTEE_ARG_TYPE_IO)
> > > >>                    qcomtee_object_put(u[i].o);
> > > >
> > > > This is not required, considering the sequence of clean up, this
> > > > would never happen. `i` at least have been accessed once in the
> > > > switch above.
> > > >
> > > > Regards,
> > > > Amir
> > > >
> > > >
> > >
> > > Also, size of u is always num_params + 1 for the ending 0.
> > > (basically means `i < num_params` can be removed).
> > >
> >
> > Yes.  This is true.
> 
> So this patch isn't needed. I'll drop it if no one objects.

The patch makes the code better though...  It never really makes sense
to use a variable first and then check if it's valid later.  In this
case the check isn't required.

Ideally the code would only have one limit.  We could either do:

	for (; i < num_params; i++) {
Or:
	for (; u[i].type != QCOMTEE_ARG_TYPE_INV; i++) {

Either way works...

regards,
dan carpenter