bpf: Don't redirect packets with invalid pkt_len

mainline inclusion
from mainline-v5.19-rc6
commit fd189422
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5HWKR
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=fd1894224407

--------------------------------

Syzbot found an issue [1]: fq_codel_drop() try to drop a flow whitout any
skbs, that is, the flow->head is null.
The root cause, as the [2] says, is because that bpf_prog_test_run_skb()
run a bpf prog which redirects empty skbs.
So we should determine whether the length of the packet modified by bpf
prog or others like bpf_prog_test is valid before forwarding it directly.

LINK: [1] https://syzkaller.appspot.com/bug?id=0b84da80c2917757915afa89f7738a9d16ec96c5
LINK: [2] https://www.spinics.net/lists/netdev/msg777503.html



Reported-by:  <syzbot+7a12909485b94426aceb@syzkaller.appspotmail.com>
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20220715115559.139691-1-shaozhengchao@huawei.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>