CVE-2024-26853

In the Linux kernel, the following vulnerability has been resolved:

igc: avoid returning frame twice in XDP_REDIRECT

When a frame can not be transmitted in XDP_REDIRECT

(e.g. due to a full queue), it is necessary to free

it by calling xdp_return_frame_rx_napi.

However, this is the responsibility of the caller of

the ndo_xdp_xmit (see for example bq_xmit_all in

kernel/bpf/devmap.c) and thus calling it inside

igc_xdp_xmit (which is the ndo_xdp_xmit of the igc

driver) as well will lead to memory corruption.

In fact, bq_xmit_all expects that it can return all

frames after the last successfully transmitted one.

Therefore, break for the first not transmitted frame,

but do not call xdp_return_frame_rx_napi in igc_xdp_xmit.

This is equally implemented in other Intel drivers

such as the igb.

There are two alternatives to this that were rejected:

1. Return num_frames as all the frames would have been

transmitted and release them inside igc_xdp_xmit.

While it might work technically, it is not what

the return value is meant to represent (i.e. the

number of SUCCESSFULLY transmitted packets).

2. Rework kernel/bpf/devmap.c and all drivers to

support non-consecutively dropped packets.

Besides being complex, it likely has a negative

performance impact without a significant gain

since it is anyway unlikely that the next frame

can be transmitted if the previous one was dropped.

The memory corruption can be reproduced with

the following script which leads to a kernel panic

after a few seconds. It basically generates more

traffic than a i225 NIC can transmit and pushes it

via XDP_REDIRECT from a virtual interface to the

physical interface where frames get dropped.

#!/bin/bash

INTERFACE=enp4s0

INTERFACE_IDX=`cat /sys/class/net/$INTERFACE/ifindex`

sudo ip link add dev veth1 type veth peer name veth2

sudo ip link set up $INTERFACE

sudo ip link set up veth1

sudo ip link set up veth2

cat << EOF > redirect.bpf.c

SEC("prog")

int redirect(struct xdp_md *ctx)

{

return bpf_redirect($INTERFACE_IDX, 0);

}

char _license[] SEC("license") = "GPL";

EOF

clang -O2 -g -Wall -target bpf -c redirect.bpf.c -o redirect.bpf.o

sudo ip link set veth2 xdp obj redirect.bpf.o

cat << EOF > pass.bpf.c

SEC("prog")

int pass(struct xdp_md *ctx)

{

return XDP_PASS;

}

char _license[] SEC("license") = "GPL";

EOF

clang -O2 -g -Wall -target bpf -c pass.bpf.c -o pass.bpf.o

sudo ip link set $INTERFACE xdp obj pass.bpf.o

cat << EOF > trafgen.cfg

{

/* Ethernet Header */

0xe8, 0x6a, 0x64, 0x41, 0xbf, 0x46,

0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,

const16(ETH_P_IP),

/* IPv4 Header */

0b01000101, 0, # IPv4 version, IHL, TOS

const16(1028), # IPv4 total length (UDP length + 20 bytes (IP header))

const16(2), # IPv4 ident

0b01000000, 0, # IPv4 flags, fragmentation off

64, # IPv4 TTL

17, # Protocol UDP

csumip(14, 33), # IPv4 checksum

/* UDP Header */

10, 0, 1, 1, # IP Src - adapt as needed

10, 0, 1, 2, # IP Dest - adapt as needed

const16(6666), # UDP Src Port

const16(6666), # UDP Dest Port

const16(1008), # UDP length (UDP header 8 bytes + payload length)

csumudp(14, 34), # UDP checksum

/* Payload */

fill('W', 1000),

}

EOF

sudo trafgen -i trafgen.cfg -b3000MB -o veth1 --cpp