On Thu, Dec 14, 2023 at 12:38 PM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: > > While testing, I happened to notice a random crash that looked like: > > Kernel panic - not syncing: stack-protector: > Kernel stack is corrupted in: drm_dp_dpcd_probe+0x120/0x120 > > Analysis of drm_dp_dpcd_probe() shows that we pass in a 1-byte buffer > (allocated on the stack) to the aux->transfer() function. Presumably > if the aux->transfer() writes more than one byte to this buffer then > we're in a bad shape. > > Dropping into kgdb, I noticed that "aux->transfer" pointed at > ps8640_aux_transfer(). > > Reading through ps8640_aux_transfer(), I can see that there are cases > where it could write more bytes to msg->buffer than were specified by > msg->size. This could happen if the hardware reported back something > bogus to us. Let's fix this so we never write more than msg->size > bytes. We'll still read all the bytes from the hardware just in case > the hardware requires it since the aux transfer data comes through an > auto-incrementing register. > > NOTE: I have no actual way to reproduce this issue but it seems likely > this is what was happening in the crash I looked at. > > Fixes: 13afcdd7277e ("drm/bridge: parade-ps8640: Add support for AUX channel") > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> Reviewed-by: Guenter Roeck <groeck@xxxxxxxxxxxx> > --- > > Changes in v3: > - Never return more than msg->size as the number of bytes we read. > > Changes in v2: > - Still read all the bytes; just don't write them all to the buffer. > > drivers/gpu/drm/bridge/parade-ps8640.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c > index 8161b1a1a4b1..d264b80d909d 100644 > --- a/drivers/gpu/drm/bridge/parade-ps8640.c > +++ b/drivers/gpu/drm/bridge/parade-ps8640.c > @@ -330,11 +330,12 @@ static ssize_t ps8640_aux_transfer_msg(struct drm_dp_aux *aux, > return ret; > } > > - buf[i] = data; > + if (i < msg->size) > + buf[i] = data; > } > } > > - return len; > + return min(len, msg->size); > } > > static ssize_t ps8640_aux_transfer(struct drm_dp_aux *aux, > -- > 2.43.0.472.g3155946c3a-goog >