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 increase the length.
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>
---
drivers/gpu/drm/bridge/parade-ps8640.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
index 8161b1a1a4b1..fb2ec4264549 100644
--- a/drivers/gpu/drm/bridge/parade-ps8640.c
+++ b/drivers/gpu/drm/bridge/parade-ps8640.c
@@ -302,7 +302,7 @@ static ssize_t ps8640_aux_transfer_msg(struct drm_dp_aux *aux,
fallthrough;
case SWAUX_STATUS_ACKM:
- len = data & SWAUX_M_MASK;
+ len = min(len, (unsigned int)(data & SWAUX_M_MASK));
break;
case SWAUX_STATUS_DEFER:
case SWAUX_STATUS_I2C_DEFER:
@@ -310,7 +310,7 @@ static ssize_t ps8640_aux_transfer_msg(struct drm_dp_aux *aux,
msg->reply |= DP_AUX_NATIVE_REPLY_DEFER;
else
msg->reply |= DP_AUX_I2C_REPLY_DEFER;
- len = data & SWAUX_M_MASK;
+ len = min(len, (unsigned int)(data & SWAUX_M_MASK));
break;
case SWAUX_STATUS_INVALID:
return -EOPNOTSUPP;
--
2.43.0.472.g3155946c3a-goog
