Re: [PATCH 1/5 v4] accel/qaic: tighten bounds checking in encode_message()

From: Jeffrey Hugo
Date: Fri Jul 14 2023 - 12:03:05 EST


On 7/14/2023 5:41 AM, Pranjal Ramajor Asha Kanojiya wrote:


On 7/11/2023 1:50 PM, Dan Carpenter wrote:
There are several issues in this code.  The check at the start of the
loop:

    if (user_len >= user_msg->len) {

This check does not ensure that we have enough space for the trans_hdr
(8 bytes).  Instead the check needs to be:

    if (user_len > user_msg->len - sizeof(*trans_hdr)) {

That subtraction is done as an unsigned long we want to avoid
negatives.  Add a lower bound to the start of the function.

    if (user_msg->len < sizeof(*trans_hdr))

There is a second integer underflow which can happen if
trans_hdr->len is zero inside the encode_passthrough() function.

    memcpy(out_trans->data, in_trans->data, in_trans->hdr.len - sizeof(in_trans->hdr));

Instead of adding a check to encode_passthrough() it's better to check
in this central place.  Add that check:

    if (trans_hdr->len < sizeof(trans_hdr)

The final concern is that the "user_len + trans_hdr->len" might have an
integer overflow bug.  Use size_add() to prevent that.

-    if (user_len + trans_hdr->len > user_msg->len) {
+    if (size_add(user_len, trans_hdr->len) > user_msg->len) {

Fixes: 129776ac2e38 ("accel/qaic: Add control path")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

Reviewed-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@xxxxxxxxxxx>


Applied to drm-misc-fixes

-Jeff