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

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

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>