[PATCH wireless] wifi: mm81x: validate YAPS receive framing

[Felix Hoffmann]

The receive byte count comes from device-controlled status registers, but
the packet splitter unconditionally consumes a four-byte delimiter. A count
of one to three bytes therefore makes bytes_remaining negative. If the
reused receive buffer contains a valid delimiter, the negative value is
passed to memcpy() and converted to a near-SIZE_MAX length, corrupting
kernel memory.

YAPS streams are word aligned, so reject byte counts that cannot contain
complete delimiters. Also reject delimiter sizes which do not leave any
packet data after removing the reserved metadata page.

Fixes: b1906cea00b0 ("wifi: mm81x: add mm81x Wi-Fi HaLow driver")
Assisted-by: Codex:gpt-5
Signed-off-by: Felix Hoffmann <f3lix.dev@xxxxxx>
---
 drivers/net/wireless/morsemicro/mm81x/yaps_hw.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/morsemicro/mm81x/yaps_hw.c b/drivers/net/wireless/morsemicro/mm81x/yaps_hw.c
index 3d641d23c35b..97b2ff93c69f 100644
--- a/drivers/net/wireless/morsemicro/mm81x/yaps_hw.c
+++ b/drivers/net/wireless/morsemicro/mm81x/yaps_hw.c
@@ -407,7 +407,7 @@ static bool mm81x_read_pkts_h_is_valid_delim(u32 delim)
 	if (calc_crc != YAPS_DELIM_GET_CRC(delim))
 		return false;
 
-	if (pkt_size == 0)
+	if (pkt_size <= YAPS_RESERVED_PAGE_SIZE)
 		return false;
 
 	if ((pkt_size + padding) > YAPS_MAX_PKT_SIZE_BYTES)
@@ -455,6 +455,10 @@ static int mm81x_yaps_hw_read_pkts(struct mm81x_yaps *yaps,
 		return 0;
 	if (bytes_remaining < 0)
 		return bytes_remaining;
+	if (!IS_ALIGNED(bytes_remaining, sizeof(u32))) {
+		dev_warn(yaps->mors->dev, "yaps truncated delimiter");
+		return -EIO;
+	}
 
 	if (bytes_remaining > YAPS_HW_WINDOW_SIZE_BYTES) {
 		bytes_remaining = YAPS_HW_WINDOW_SIZE_BYTES;
-- 
2.43.0