[PATCH 5.6] mt76: fix array overflow on receiving too many fragments for a packet

[Felix Fietkau <nbd@nbd.name>]

If the hardware receives an oversized packet with too many rx fragments,
skb_shinfo(skb)->frags can overflow and corrupt memory of adjacent pages.
This becomes especially visible if it corrupts the freelist pointer of
a slab page.

Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 drivers/net/wireless/mediatek/mt76/dma.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/dma.c b/drivers/net/wireless/mediatek/mt76/dma.c
index 6173c80189ba..1847f55e199b 100644
--- a/drivers/net/wireless/mediatek/mt76/dma.c
+++ b/drivers/net/wireless/mediatek/mt76/dma.c
@@ -447,10 +447,13 @@ mt76_add_fragment(struct mt76_dev *dev, struct mt76_queue *q, void *data,
 	struct page *page = virt_to_head_page(data);
 	int offset = data - page_address(page);
 	struct sk_buff *skb = q->rx_head;
+	struct skb_shared_info *shinfo = skb_shinfo(skb);
 
-	offset += q->buf_offset;
-	skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page, offset, len,
-			q->buf_size);
+	if (shinfo->nr_frags < ARRAY_SIZE(shinfo->frags)) {
+		offset += q->buf_offset;
+		skb_add_rx_frag(skb, shinfo->nr_frags, page, offset, len,
+				q->buf_size);
+	}
 
 	if (more)
 		return;
-- 
2.24.0