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