Messages in this thread Patch in this message | | | From | Douglas Anderson <> | Subject | [PATCH v3 1/2] drm/bridge: parade-ps8640: Never store more than msg->size bytes in AUX xfer | Date | Thu, 14 Dec 2023 12:37:51 -0800 |
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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@chromium.org> ---
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
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