Hi, On Tue, Jun 30, 2026 at 11:44 PM Maoyi Xie <[email protected]> wrote: > > tc_aux_transfer() clamps an AUX read to the payload limit: > > size_t size = min_t(size_t, DP_AUX_MAX_PAYLOAD_BYTES - 1, msg->size); > > After the transfer it replaces size with the byte count the controller > reports in AUX_BYTES: > > if (size) > size = FIELD_GET(AUX_BYTES, auxstatus); > > AUX_BYTES is GENMASK(15, 8), so it can be up to 255. Nothing clamps it > back to the request. tc_aux_read_data() reads that many bytes into the > 16-byte auxrdata stack buffer, then copies them into the caller buffer. A > reported count of 255 makes the read run to 256 bytes and overruns both. > > The controller should never report more than it was asked to transfer, so > this is defense in depth rather than a live hole. The reported count is > only lightly trusted, and the check is cheap. Clamp it back to the request, > the same way ti-sn65dsi86 does in commit aca58eac52b8 ("drm/bridge: > ti-sn65dsi86: Never store more than msg->size bytes in AUX xfer"). > > Fixes: 12dfe7c4d9c5 ("drm/bridge: tc358767: Use reported AUX transfer size") > Co-developed-by: Kaixuan Li <[email protected]> > Signed-off-by: Kaixuan Li <[email protected]> > Signed-off-by: Maoyi Xie <[email protected]> > --- > drivers/gpu/drm/bridge/tc358767.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/bridge/tc358767.c > b/drivers/gpu/drm/bridge/tc358767.c > index 4097fef4b8..26ba5a6c1b 100644 > --- a/drivers/gpu/drm/bridge/tc358767.c > +++ b/drivers/gpu/drm/bridge/tc358767.c > @@ -527,7 +527,7 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux, > * address-only transfer > */ > if (size) > - size = FIELD_GET(AUX_BYTES, auxstatus); > + size = min_t(size_t, size, FIELD_GET(AUX_BYTES, auxstatus));
Being super nitty: we don't technically need the "if (size)" above anymore since it will be handled by the "min". Then again, if we remove it then we also ahve to rework the comment about the "if" test... :-P ...so I'm going to say this is fine the way it is. Reviewed-by: Douglas Anderson <[email protected]> I'll try to land next week unless someone else objects. Another committer is free to land before that if they feel like it. -Doug
