[PATCH 2/5 v3] accel/qaic: tighten bounds checking in decode_message()

[Dan Carpenter]

Copy the bounds checking from encode_message() to decode_message().

This patch addresses the following concerns.  Ensure that there is
enough space for at least one header so that we don't have a negative
size later.

	if (msg_hdr_len < sizeof(*trans_hdr))

Ensure that we have enough space to read the next header from the
msg->data.

	if (msg_len > msg_hdr_len - sizeof(*trans_hdr))
		return -EINVAL;

Check that the trans_hdr->len is not below the minimum size:

	if (hdr_len < sizeof(*trans_hdr))

This minimum check ensures that we don't corrupt memory in
decode_passthrough() when we do.

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

And finally, use size_add() to prevent an integer overflow:

	if (size_add(msg_len, hdr_len) > msg_hdr_len)

Fixes: 129776ac2e38 ("accel/qaic: Add control path")
Signed-off-by: Dan Carpenter <dan.carpenter at linaro.org>
---
v2: Fix the >= vs > bug in "if (msg_len > msg_hdr_len - sizeof(*trans_hdr))"
---
 drivers/accel/qaic/qaic_control.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/accel/qaic/qaic_control.c b/drivers/accel/qaic/qaic_control.c
index 2fdd5959c52f..752b67aff777 100644
--- a/drivers/accel/qaic/qaic_control.c
+++ b/drivers/accel/qaic/qaic_control.c
@@ -956,15 +956,23 @@ static int decode_message(struct qaic_device *qdev, struct manage_msg *user_msg,
 	int ret;
 	int i;
 
-	if (msg_hdr_len > QAIC_MANAGE_MAX_MSG_LENGTH)
+	if (msg_hdr_len < sizeof(*trans_hdr) ||
+	    msg_hdr_len > QAIC_MANAGE_MAX_MSG_LENGTH)
 		return -EINVAL;
 
 	user_msg->len = 0;
 	user_msg->count = le32_to_cpu(msg->hdr.count);
 
 	for (i = 0; i < user_msg->count; ++i) {
+		u32 hdr_len;
+
+		if (msg_len > msg_hdr_len - sizeof(*trans_hdr))
+			return -EINVAL;
+
 		trans_hdr = (struct wire_trans_hdr *)(msg->data + msg_len);
-		if (msg_len + le32_to_cpu(trans_hdr->len) > msg_hdr_len)
+		hdr_len = le32_to_cpu(trans_hdr->len);
+		if (hdr_len < sizeof(*trans_hdr) ||
+		    size_add(msg_len, hdr_len) > msg_hdr_len)
 			return -EINVAL;
 
 		switch (le32_to_cpu(trans_hdr->type)) {
-- 
2.39.2