skb_do_redirect returns various of values: error code (negative), 0 (success), and some positive status code, e.g. NET_XMIT_CN, NET_RX_DROP. Such code are not handled at lwt xmit hook in function ip_finish_output2 and ip6_finish_output, which can cause unexpected problems. This change converts the positive status code to proper error code.

Suggested-by: Stanislav Fomichev sdf@google.com Reported-by: Jordan Griege jgriege@cloudflare.com Signed-off-by: Yan Zhai yan@cloudflare.com

--- v3: converts also RX side return value in addition to TX values v2: code style change suggested by Stanislav Fomichev --- net/core/filter.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c index 06ba0e56e369..3e232ce11ca0 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2095,7 +2095,12 @@ static const struct bpf_func_proto bpf_csum_level_proto = {

static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb) { - return dev_forward_skb_nomtu(dev, skb); + int ret = dev_forward_skb_nomtu(dev, skb); + + if (unlikely(ret > 0)) + return -ENETDOWN; + + return 0; }

static inline int __bpf_rx_skb_no_mac(struct net_device *dev, @@ -2106,6 +2111,8 @@ static inline int __bpf_rx_skb_no_mac(struct net_device *dev, if (likely(!ret)) { skb->dev = dev; ret = netif_rx(skb); + } else if (ret > 0) { + return -ENETDOWN; }

return ret; @@ -2129,6 +2136,9 @@ static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb) ret = dev_queue_xmit(skb); dev_xmit_recursion_dec();

+ if (unlikely(ret > 0)) + ret = net_xmit_errno(ret); + return ret; }

Tests BPF redirect at the lwt xmit hook to ensure error handling are safe, i.e. won't panic the kernel.

Suggested-by: Alexei Starovoitov alexei.starovoitov@gmail.com Signed-off-by: Yan Zhai yan@cloudflare.com --- tools/testing/selftests/bpf/Makefile | 1 + .../selftests/bpf/progs/test_lwt_redirect.c | 67 +++++++ .../selftests/bpf/test_lwt_redirect.sh | 165 ++++++++++++++++++ 3 files changed, 233 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/test_lwt_redirect.c create mode 100755 tools/testing/selftests/bpf/test_lwt_redirect.sh

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 538df8fb8c42..e3a24d053793 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -66,6 +66,7 @@ TEST_PROGS := test_kmod.sh \ test_xdp_vlan_mode_generic.sh \ test_xdp_vlan_mode_native.sh \ test_lwt_ip_encap.sh \ + test_lwt_redirect.sh \ test_tcp_check_syncookie.sh \ test_tc_tunnel.sh \ test_tc_edt.sh \ diff --git a/tools/testing/selftests/bpf/progs/test_lwt_redirect.c b/tools/testing/selftests/bpf/progs/test_lwt_redirect.c new file mode 100644 index 000000000000..622c6b1e7128 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_lwt_redirect.c @@ -0,0 +1,67 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/bpf.h> +#include <bpf/bpf_helpers.h> + +#define ETH_LEN 14 + +/* We don't care about whether the packet can be received by network stack. + * Just care if the packet is sent to the correct device at correct direction + * and not panic the kernel. + */ +static __always_inline int prepend_dummy_mac(struct __sk_buff *skb) +{ + char mac[] = {0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0xf, + 0xe, 0xd, 0xc, 0xb, 0xa, 0x08, 0x00}; + + if (bpf_skb_change_head(skb, ETH_LEN, 0)) { + bpf_printk("%s: fail to change head", __func__); + return -1; + } + + if (bpf_skb_store_bytes(skb, 0, mac, sizeof(mac), 0)) { + bpf_printk("%s: fail to update mac", __func__); + return -1; + } + + return 0; +} + +SEC("redir_ingress") +int test_lwt_redirect_in(struct __sk_buff *skb) +{ + if (prepend_dummy_mac(skb)) + return BPF_DROP; + + bpf_printk("Redirect skb to link %d ingress", skb->mark); + return bpf_redirect(skb->mark, BPF_F_INGRESS); +} + +SEC("redir_egress") +int test_lwt_redirect_out(struct __sk_buff *skb) +{ + if (prepend_dummy_mac(skb)) + return BPF_DROP; + + bpf_printk("Redirect skb to link %d egress", skb->mark); + return bpf_redirect(skb->mark, 0); +} + +SEC("redir_egress_nomac") +int test_lwt_redirect_out_nomac(struct __sk_buff *skb) +{ + int ret = bpf_redirect(skb->mark, 0); + + bpf_printk("Redirect skb to link %d egress nomac: %d", skb->mark, ret); + return ret; +} + +SEC("redir_ingress_nomac") +int test_lwt_redirect_in_nomac(struct __sk_buff *skb) +{ + int ret = bpf_redirect(skb->mark, BPF_F_INGRESS); + + bpf_printk("Redirect skb to link %d ingress nomac: %d", skb->mark, ret); + return ret; +} + +char _license[] SEC("license") = "GPL"; diff --git a/tools/testing/selftests/bpf/test_lwt_redirect.sh b/tools/testing/selftests/bpf/test_lwt_redirect.sh new file mode 100755 index 000000000000..fe97cbc40ee8 --- /dev/null +++ b/tools/testing/selftests/bpf/test_lwt_redirect.sh @@ -0,0 +1,165 @@ +#!/bin/bash +# SPDX-License-Identifier: GPL-2.0 +# +# This regression test checks basic lwt redirect functionality, +# making sure the kernel would not crash when redirecting packets +# to a device, regardless its administration state: +# +# 1. redirect to a device egress/ingress should work normally +# 2. redirect to a device egress/ingress should not panic when target is down +# 3. redirect to a device egress/ingress should not panic when target carrier is down +# +# All test setup are simple: redirect ping packet via lwt xmit to cover above +# situations. We do not worry about specific device type, except for the two +# categories of devices that require MAC header and not require MAC header. For +# carrier down situation, we use a vlan device as upper link, and bring down its +# lower device. +# +# Kselftest framework requirement - SKIP code is 4. +ksft_skip=4 +BPF_FILE="test_lwt_redirect.bpf.o" +INGRESS_REDIR_IP=2.2.2.2 +EGRESS_REDIR_IP=3.3.3.3 +INGRESS_REDIR_IP_NOMAC=4.4.4.4 +EGRESS_REDIR_IP_NOMAC=5.5.5.5 +PASS=0 +FAIL=0 + +readonly NS1="ns1-$(mktemp -u XXXXXX)" + +msg="skip all tests:" +if [ $UID != 0 ]; then + echo $msg please run this as root >&2 + exit $ksft_skip +fi + +get_ip_direction() { + case $1 in + $INGRESS_REDIR_IP|$INGRESS_REDIR_IP_NOMAC) + echo ingress + ;; + $EGRESS_REDIR_IP|$EGRESS_REDIR_IP_NOMAC) + echo egress + ;; + *) + echo bug + ;; + esac +} + +test_pass() +{ + local testname=$1 + local direction=`get_ip_direction $2` + shift 2 + echo "Pass: $testname $direction $@" + PASS=$((PASS + 1)) +} + +test_fail() +{ + local testname=$1 + local direction=`get_ip_direction $2` + shift 2 + echo "Fail: $testname $direction $@" + FAIL=$((FAIL + 1)) +} + +setup() { + ip netns add $NS1 + + ip -n $NS1 link set lo up + ip -n $NS1 link add link_err type dummy + ip -n $NS1 link add link_w_mac type dummy + ip -n $NS1 link add link link_w_mac link_upper type vlan id 1 + ip -n $NS1 link add link_wo_mac type gre remote 4.3.2.1 local 1.2.3.4 + ip -n $NS1 link set link_err up + ip -n $NS1 link set link_w_mac up + ip -n $NS1 link set link_upper up + ip -n $NS1 link set link_wo_mac up + + ip -n $NS1 addr add dev lo 1.1.1.1/32 + ip -n $NS1 route add $INGRESS_REDIR_IP encap bpf xmit \ + obj $BPF_FILE sec redir_ingress dev link_err + ip -n $NS1 route add $EGRESS_REDIR_IP encap bpf xmit \ + obj $BPF_FILE sec redir_egress dev link_err + ip -n $NS1 route add $INGRESS_REDIR_IP_NOMAC encap bpf xmit \ + obj $BPF_FILE sec redir_ingress_nomac dev link_err + ip -n $NS1 route add $EGRESS_REDIR_IP_NOMAC encap bpf xmit \ + obj $BPF_FILE sec redir_egress_nomac dev link_err +} + +cleanup_and_summary() { + ip netns del $NS1 + echo PASSED:$PASS FAILED:$FAIL + if [ $FAIL -ne 0 ]; then + exit 1 + else + exit 0 + fi +} + +test_redirect_normal() { + local test_name=${FUNCNAME[0]} + local link_name=$1 + local link_id=`ip netns exec $NS1 cat /sys/class/net/${link_name}/ifindex` + local dest=$2 + + ip netns exec $NS1 timeout 2 tcpdump -i ${link_name} -c 1 -n -p icmp >/dev/null 2>&1 & + local jobid=$! + sleep 1 + + # hack: mark indicates the link to redirect to + ip netns exec $NS1 ping -m $link_id $dest -c 1 -w 1 > /dev/null 2>&1 + wait $jobid + + if [ $? -ne 0 ]; then + test_fail $test_name $dest $link_name + else + test_pass $test_name $dest $link_name + fi +} + +test_redirect_no_panic_on_link_down() { + local test_name=${FUNCNAME[0]} + local link_name=$1 + local link_id=`ip netns exec $NS1 cat /sys/class/net/${link_name}/ifindex` + local dest=$2 + + ip -n $NS1 link set $link_name down + # hack: mark indicates the link to redirect to + ip netns exec $NS1 ping -m $link_id $dest -c 1 -w 1 >/dev/null 2>&1 + + test_pass $test_name $dest to $link_name + ip -n $NS1 link set $link_name up +} + +test_redirect_no_panic_on_link_carrier_down() { + local test_name=${FUNCNAME[0]} + local link_id=`ip netns exec $NS1 cat /sys/class/net/link_upper/ifindex` + local dest=$1 + + ip -n $NS1 link set link_w_mac down + # hack: mark indicates the link to redirect to + ip netns exec $NS1 ping -m $link_id $dest -c 1 -w 1 >/dev/null 2>&1 + + test_pass $test_name $dest to link_upper + ip -n $NS1 link set link_w_mac up +} + +setup + +echo "Testing lwt redirect to devices requiring MAC header" +for dest in $INGRESS_REDIR_IP $EGRESS_REDIR_IP; do + test_redirect_normal link_w_mac $dest + test_redirect_no_panic_on_link_down link_w_mac $dest + test_redirect_no_panic_on_link_carrier_down $dest +done + +echo "Testing lwt redirect to devices not requiring MAC header" +for dest in $INGRESS_REDIR_IP_NOMAC $EGRESS_REDIR_IP_NOMAC; do + test_redirect_normal link_wo_mac $dest + test_redirect_no_panic_on_link_down link_wo_mac $dest +done + +cleanup_and_summary