[PATCH 6.18 128/198] net: usb: cdc-phonet: fix skb frags[] overflow in rx_complete()

Greg Kroah-Hartman
2026-04-20T16:02:44Z

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

commit 600dc40554dc5ad1e6f3af51f700228033f43ea7 upstream.

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@lunn.ch>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: stable <stable@kernel.org>
Assisted-by: gregkh_clanker_t1000
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/2026041134-dreamboat-buddhism-d1ec@gregkh
Fixes: 87cf65601e17 ("USB host CDC Phonet network interface driver")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/usb/cdc-phonet.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- 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 */