__bpf_offload_dev_match() falls back to comparing offdev pointers after an
exact netdev mismatch. Bound-only programs normally have NULL offdevs, so
unrelated netdevs compare equal. A bound-only program on an
offload-registered netdev can instead inherit a real offdev and match a
sibling port. With CAP_BPF and CAP_NET_ADMIN, a caller can use
bpf(BPF_LINK_CREATE) with a different target ifindex to run metadata kfuncs
specialized for the bound driver on the target driver's xdp_buff. Running a
veth-bound program on tun reads beyond tun's bare stack xdp_buff as a
veth_xdp_buff.
Oops: general protection fault, probably for non-canonical address
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
RIP: 0010:veth_xdp_rx_timestamp (drivers/net/veth.c:1673)
Call Trace:
...
tun_build_skb (drivers/net/tun.c:1739)
tun_get_user (drivers/net/tun.c:1856)
tun_chr_write_iter (drivers/net/tun.c:2091)
vfs_write (fs/read_write.c:595 fs/read_write.c:687)
ksys_write (fs/read_write.c:739)
do_syscall_64 (arch/x86/entry/syscall_64.c:84)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
Kernel panic - not syncing: Fatal exception in interrupt
Restrict non-offloaded programs to exact netdev matches and retain the
shared-offdev fallback only for genuinely offloaded multi-port programs.
Fixes: 2b3486bc2d ("bpf: Introduce device-bound XDP programs")
Reported-by: <co+ac0a8c41de69121d@bugs.sh>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20260917161335.1020405-2-bestswngs@gmail.com/
Link: https://patch.msgid.link/20260920132303.4109240-3-bestswngs@gmail.com
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