[PATCH net] net: usb: cdc-phonet: fix skb frags[] overflow in rx_complete()

[Greg Kroah-Hartman]

A malicious USB device claiming to be a CDC Phonet modem can overflow
the skb_shared_info->frags[] array by sending an unbounded sequence of
full-page bulk transfers.

Drop the skb and increment the length error when the frag limit is
reached.  This matches the same fix that commit f0813bcd2d9d ("net:
wwan: t7xx: fix potential skb->frags overflow in RX path") did for the
t7xx driver.

Cc: Andrew Lunn <andrew+netdev@xxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxx>
Assisted-by: gregkh_clanker_t1000
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/usb/cdc-phonet.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/cdc-phonet.c b/drivers/net/usb/cdc-phonet.c
index ad5121e9cf5d..165650ecef64 100644
--- a/drivers/net/usb/cdc-phonet.c
+++ b/drivers/net/usb/cdc-phonet.c
@@ -157,11 +157,16 @@ static void rx_complete(struct urb *req)
 						PAGE_SIZE);
 				page = NULL;
 			}
-		} else {
+		} else if (skb_shinfo(skb)->nr_frags < MAX_SKB_FRAGS) {
 			skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
 					page, 0, req->actual_length,
 					PAGE_SIZE);
 			page = NULL;
+		} else {
+			dev_kfree_skb_any(skb);
+			pnd->rx_skb = NULL;
+			skb = NULL;
+			dev->stats.rx_length_errors++;
 		}
 		if (req->actual_length < PAGE_SIZE)
 			pnd->rx_skb = NULL; /* Last fragment */
-- 
2.53.0