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[85.86.63.67]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47fd41d1956sm10157797f8f.6.2026.07.31.13.56.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Jul 2026 13:56:03 -0700 (PDT) Date: Fri, 31 Jul 2026 22:56:02 +0200 From: Pablo =?iso-8859-1?Q?Vallesp=EDn?= Aranguren To: David Laight 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: References: <20260731202629.10ff97e6@pumpkin> 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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260731202629.10ff97e6@pumpkin> On Fri, Jul 31, 2026 at 08:26:29PM +0100, David Laight wrote: > On Fri, 31 Jul 2026 20:33:34 +0200 > Pablo Vallespín Aranguren wrote: > > 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. I haven't verified how the real Xircom firmware handles runt frames (I don't own this hardware). I tested with Qemu's emulated NIC, the device itself does validate and reject negative-size values before sending them to the driver. > Of course, if you think the device might lie all bets are off. > (Without an iommu is can write anywhere in host memory...) I took into account that the hardware could glitch or a misbehaving/fake card could be used. I modified the emulated NIC to mimic this behaviour, and given that the driver does not perform a check on its own (to validate that pkt_len is not negative) it does lead to a kernel panic. Best, Pablo > > Signed-off-by: Pablo Vallespín Aranguren > > Assisted-by: gkh_clanker_t1000 > > --- > > drivers/net/ethernet/dec/tulip/xircom_cb.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/drivers/net/ethernet/dec/tulip/xircom_cb.c b/drivers/net/ethernet/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; > > > > + 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 = 1518; >