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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47fd456262bsm7841993f8f.17.2026.07.31.12.26.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Jul 2026 12:26:31 -0700 (PDT) Date: Fri, 31 Jul 2026 20:26:29 +0100 From: David Laight To: Pablo =?UTF-8?B?VmFsbGVzcMOtbg==?= Aranguren Cc: Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , "open list:TULIP NETWORK DRIVERS" , "open list:TULIP NETWORK DRIVERS" , open list , Greg KH Subject: Re: [PATCH] net: tulip: xircom_cb: drop runt frames before skb copy Message-ID: <20260731202629.10ff97e6@pumpkin> In-Reply-To: References: X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, 31 Jul 2026 20:33:34 +0200 Pablo Vallesp=C3=ADn Aranguren wrote: > investigate_read_descriptor() takes the 11-bit packet length straight > from the device-written descriptor and subtracts 4 for the CRC. A > length below 4 underflows pkt_len to a negative value, which is then > passed to skb_put_data() as a huge unsigned length and corrupts memory > past the end of the freshly allocated skb. Have you checked that that hardware can actually set a short value? I'd expect that packets shorter than 64 bytes (including the crc) are dropped as 'runts' and probably don't even use a ring entry. Of course, if you think the device might lie all bets are off. (Without an iommu is can write anywhere in host memory...) David >=20 > Drop the frame as a length error if pkt_len is negative after CRC > removal. >=20 > Signed-off-by: Pablo Vallesp=C3=ADn Aranguren > Assisted-by: gkh_clanker_t1000 > --- > drivers/net/ethernet/dec/tulip/xircom_cb.c | 5 +++++ > 1 file changed, 5 insertions(+) >=20 > diff --git a/drivers/net/ethernet/dec/tulip/xircom_cb.c b/drivers/net/eth= ernet/dec/tulip/xircom_cb.c > index e5d2ede13845..62c64da1c8fa 100644 > --- a/drivers/net/ethernet/dec/tulip/xircom_cb.c > +++ b/drivers/net/ethernet/dec/tulip/xircom_cb.c > @@ -1110,6 +1110,11 @@ investigate_read_descriptor(struct net_device *dev= , struct xircom_private *card, > /* minus 4, we don't want the CRC */ > struct sk_buff *skb; > =20 > + if (pkt_len < 0) { > + dev->stats.rx_length_errors++; > + goto out; > + } > + > if (pkt_len > 1518) { > netdev_err(dev, "Packet length %i is bogus\n", pkt_len); > pkt_len =3D 1518;