[PATCH v4 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 validating that the buffer has sufficient
space. If the total reassembled payload exceeds the receive buffer
capacity, this results in a heap buffer overflow.

Additionally, the return values of recvframe_pull() and
recvframe_pull_tail() were ignored. On failure those helpers revert
their pointer updates and return NULL; continuing past such a
failure would leave pfhdr->rx_tail at its pre-strip value, so the
subsequent bounds check against rx_end - rx_tail would operate on
stale pointers.

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

Check the return values of recvframe_pull() and recvframe_pull_tail(),
then verify that the fragment payload fits within the remaining
buffer space before the memcpy().

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

Fixes: 554c0a3abf216 ("staging: Add rtl8723bs sdio wifi driver")
Cc: stable@vger.kernel.org
Signed-off-by: Delene Tchio Romuald <delenetchior1@gmail.com>
---
v4: check return values of recvframe_pull() and recvframe_pull_tail();
    drop unnecessary (uint) cast; add Fixes: tag and Cc: stable
    (Dan Carpenter). Luka Gejak's Reviewed-by dropped because the
    code changed.
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).

 drivers/staging/rtl8723bs/core/rtw_recv.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index f78194d508dfc..a739c2bada2a1 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -1127,12 +1127,26 @@ static union recv_frame *recvframe_defrag(struct adapter *adapter,
 
 		wlanhdr_offset = pnfhdr->attrib.hdrlen + pnfhdr->attrib.iv_len;
 
-		recvframe_pull(pnextrframe, wlanhdr_offset);
+		if (!recvframe_pull(pnextrframe, wlanhdr_offset)) {
+			rtw_free_recvframe(prframe, pfree_recv_queue);
+			rtw_free_recvframe_queue(defrag_q, pfree_recv_queue);
+			return NULL;
+		}
 
 		/* append  to first fragment frame's tail (if privacy frame, pull the ICV) */
-		recvframe_pull_tail(prframe, pfhdr->attrib.icv_len);
+		if (!recvframe_pull_tail(prframe, pfhdr->attrib.icv_len)) {
+			rtw_free_recvframe(prframe, pfree_recv_queue);
+			rtw_free_recvframe_queue(defrag_q, pfree_recv_queue);
+			return NULL;
+		}
+
+		/* Verify the receiving buffer has enough space for the fragment */
+		if (pnfhdr->len > 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 */
 		memcpy(pfhdr->rx_tail, pnfhdr->rx_data, pnfhdr->len);
 
 		recvframe_put(prframe, pnfhdr->len);
-- 
2.43.0