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Exact
Martynas Pumputis 2d7ebcb5d8 bpf: Derive source IP addr via bpf_*_fib_lookup() 
commit dab4e1f06c upstream.

Extend the bpf_fib_lookup() helper by making it to return the source
IPv4/IPv6 address if the BPF_FIB_LOOKUP_SRC flag is set.

For example, the following snippet can be used to derive the desired
source IP address:

    struct bpf_fib_lookup p = { .ipv4_dst = ip4->daddr };

    ret = bpf_skb_fib_lookup(skb, p, sizeof(p),
            BPF_FIB_LOOKUP_SRC | BPF_FIB_LOOKUP_SKIP_NEIGH);
    if (ret != BPF_FIB_LKUP_RET_SUCCESS)
        return TC_ACT_SHOT;

    /* the p.ipv4_src now contains the source address */

The inability to derive the proper source address may cause malfunctions
in BPF-based dataplanes for hosts containing netdevs with more than one
routable IP address or for multi-homed hosts.

For example, Cilium implements packet masquerading in BPF. If an
egressing netdev to which the Cilium's BPF prog is attached has
multiple IP addresses, then only one [hardcoded] IP address can be used for
masquerading. This breaks connectivity if any other IP address should have
been selected instead, for example, when a public and private addresses
are attached to the same egress interface.

The change was tested with Cilium [1].

Nikolay Aleksandrov helped to figure out the IPv6 addr selection.

[1]: https://github.com/cilium/cilium/pull/28283

Signed-off-by: Martynas Pumputis <m@lambda.lt>
Link: https://lore.kernel.org/r/20231007081415.33502-2-m@lambda.lt
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2024-03-06 14:45:20 +00:00
..
tc_act headers: Remove some left-over license text 2022-09-27 07:48:01 -07:00
bpf.h bpf: Derive source IP addr via bpf_*_fib_lookup() 2024-03-06 14:45:20 +00:00
bpf_common.h
bpf_perf_event.h
btf.h bpf: Add btf enum64 support 2022-06-07 10:20:42 -07:00
const.h
erspan.h
ethtool.h
fadvise.h
fcntl.h
filter.h
fs.h treewide: uapi: Replace zero-length arrays with flexible-array members 2022-06-28 21:26:05 +02:00
fscrypt.h tools headers UAPI: Sync linux/fscrypt.h with the kernel sources 2022-08-19 15:30:33 -03:00
hw_breakpoint.h
if_link.h Bonding: add per-port priority for failover re-selection 2022-06-24 11:27:59 +01:00
if_tun.h treewide: uapi: Replace zero-length arrays with flexible-array members 2022-06-28 21:26:05 +02:00
if_xdp.h
in.h tools headers UAPI: Sync the linux/in.h with the kernel sources 2023-06-05 09:26:22 +02:00
kcmp.h
kvm.h tools: include: sync include/api/linux/kvm.h 2022-10-22 07:54:19 -04:00
mman.h
mount.h
netlink.h
openat2.h
perf_event.h tools headers UAPI: Sync linux/perf_event.h with the kernel sources 2022-10-26 10:45:16 -03:00
pkt_cls.h treewide: uapi: Replace zero-length arrays with flexible-array members 2022-06-28 21:26:05 +02:00
pkt_sched.h
prctl.h tools headers UAPI: Sync linux/prctl.h with the kernel sources 2022-06-19 11:42:25 -03:00
sched.h
seg6.h treewide: uapi: Replace zero-length arrays with flexible-array members 2022-06-28 21:26:05 +02:00
seg6_local.h
stat.h tools headers uapi: Sync linux/stat.h with the kernel sources 2022-10-25 17:40:48 -03:00
stddef.h tools/headers: Pull in stddef.h to uapi to fix BPF selftests build in CI 2022-11-03 13:45:21 +01:00
tcp.h
tls.h
types.h
usbdevice_fs.h treewide: uapi: Replace zero-length arrays with flexible-array members 2022-06-28 21:26:05 +02:00
vhost.h tools include UAPI: Sync linux/vhost.h with the kernel sources 2022-08-19 15:30:34 -03:00