[PATCH] net: fec: reject oversized fragments before bounce-buffer memcpy

[Aldo Ariel Panzardo <qwe.aldo@gmail.com>]

fec_enet_txq_submit_frag_skb() and fec_enet_txq_submit_skb() copy
transmit data into a per-ring bounce buffer when the source address is
misaligned or the FEC_QUIRK_SWAP_FRAME quirk is active. The bounce
buffers are allocated as kmalloc(FEC_ENET_TX_FRSIZE) where
FEC_ENET_TX_FRSIZE is 2048 bytes.

However, skb_frag_size() can return up to PAGE_SIZE (4096 on most
architectures) for scatter-gather fragments, and skb_headlen() can
exceed 2048 for certain GSO packets. When this happens the memcpy
overflows the bounce buffer by up to 2048 bytes, corrupting adjacent
heap objects.

Add a length check before each bounce-buffer copy. If the data exceeds
the bounce buffer capacity, fall through to the error path rather than
performing the out-of-bounds write.

Fixes: 6605b730c061 ("FEC: Add alignment handling for FEC driver")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
 drivers/net/ethernet/freescale/fec_main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 794ec42..8614984 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -558,6 +558,8 @@ fec_enet_txq_submit_frag_skb(struct fec_enet_priv_tx_q *txq,
 		index = fec_enet_get_bd_index(bdp, &txq->bd);
 		if (((unsigned long) bufaddr) & fep->tx_align ||
 			fep->quirks & FEC_QUIRK_SWAP_FRAME) {
+			if (frag_len > FEC_ENET_TX_FRSIZE)
+				goto dma_mapping_error;
 			memcpy(txq->tx_bounce[index], bufaddr, frag_len);
 			bufaddr = txq->tx_bounce[index];
 
@@ -634,6 +636,8 @@ static int fec_enet_txq_submit_skb(struct fec_enet_priv_tx_q *txq,
 	index = fec_enet_get_bd_index(bdp, &txq->bd);
 	if (((unsigned long) bufaddr) & fep->tx_align ||
 		fep->quirks & FEC_QUIRK_SWAP_FRAME) {
+		if (buflen > FEC_ENET_TX_FRSIZE)
+			goto release;
 		memcpy(txq->tx_bounce[index], skb->data, buflen);
 		bufaddr = txq->tx_bounce[index];
 
-- 
2.43.0