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0dfcb68a6a
bpf_ipv4_fib_lookup() and bpf_ipv6_fib_lookup() build the flow key on
the stack with a bare "struct flowi4 fl4;" / "struct flowi6 fl6;" and
fill it field by field, but never set flowi4_l3mdev / flowi6_l3mdev.
On the non-DIRECT path the lookup goes through the fib rules whenever the
netns has custom rules, which a VRF installs:
bpf_ipv4_fib_lookup() -> fib_lookup() -> __fib_lookup()
-> l3mdev_update_flow() reads !fl->flowi_l3mdev
-> fib_rules_lookup() -> fib_rule_match()
-> l3mdev_fib_rule_match() uses fl->flowi_l3mdev
l3mdev_update_flow() resolves the l3mdev master from the ingress device
only while the field is still zero. Left at a nonzero stack value the
resolution is skipped, and l3mdev_fib_rule_match() then tests that value
as an ifindex, so the VRF master is not resolved and the rule fails to
match: an ingress enslaved to a VRF can fail to select its table. FIB
rules matching on an L3 master device (l3mdev_fib_rule_iif_match()/
_oif_match()) read the same value, so an "ip rule iif/oif <vrf>"
mismatches the same way.
Zero-initialize the whole flow struct rather than adding one more
field assignment, so any flowi field added later is covered too.
ip_route_input_slow() likewise zeroes the field before its input lookup.
CONFIG_INIT_STACK_ALL_ZERO masks this by default, but it depends on
compiler support (CC_HAS_AUTO_VAR_INIT_ZERO), so INIT_STACK_NONE builds,
including older toolchains that fall back to it, are exposed. Built with
INIT_STACK_ALL_PATTERN, a plain bpf_fib_lookup (no VLAN, no DIRECT) over a
VRF slave whose destination is routed only in the VRF table returns
BPF_FIB_LKUP_RET_NOT_FWDED, and resolves with this patch. On the default
config the lookup succeeds either way, so ordinary testing does not catch
the bug.
Fixes:
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Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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