[PATCH v3 1/5] staging: rtl8723bs: fix heap buffer overflow in recvframe_defrag()

[Delene Tchio Romuald <delenetchior1@gmail.com>]

In recvframe_defrag(), a memcpy() copies fragment data into the
reassembly buffer before recvframe_put() validates that the buffer
has sufficient space. If the total reassembled payload exceeds the
receive buffer capacity, this results in a heap buffer overflow.

An attacker within WiFi radio range can exploit this by sending
crafted 802.11 fragmented frames. No authentication is required.

Add a bounds check before the memcpy() to verify that the fragment
payload fits within the remaining buffer space, using the same error
handling pattern already present in the function.

Found by reviewing memory operations in the driver and tracing
buffer pointer manipulation through rtw_recv.h inline helpers.
Not tested on hardware.

Signed-off-by: Delene Tchio Romuald <delenetchior1@gmail.com>
---
v3:
 - Rebased on staging-next
 - Sent as numbered series with proper Cc from get_maintainer.pl
v2:
 - Rebased on staging-next (v1 was based on v7.0-rc6 and did not apply)
 - Removed Cc: stable (will be added by maintainer)

 drivers/staging/rtl8723bs/core/rtw_recv.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index f78194d508dfc..717e0594d983a 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -1132,7 +1132,13 @@ static union recv_frame *recvframe_defrag(struct adapter *adapter,
 		/* append  to first fragment frame's tail (if privacy frame, pull the ICV) */
 		recvframe_pull_tail(prframe, pfhdr->attrib.icv_len);
 
-		/* memcpy */
+		/* Verify the receiving buffer has enough space for the fragment */
+		if (pnfhdr->len > (uint)(pfhdr->rx_end - pfhdr->rx_tail)) {
+			rtw_free_recvframe(prframe, pfree_recv_queue);
+			rtw_free_recvframe_queue(defrag_q, pfree_recv_queue);
+			return NULL;
+		}
+
 		memcpy(pfhdr->rx_tail, pnfhdr->rx_data, pnfhdr->len);
 
 		recvframe_put(prframe, pnfhdr->len);
-- 
2.43.0