bpf: reconcile bpf_tail_call and stack_depth
The next set of patches will take advantage of stack_depth tracking, so make sure that the program that does bpf_tail_call() has stack depth large enough for the callee. We could have tracked the stack depth of the prog_array owner program and only allow insertion of the programs with stack depth less than the owner, but it will break existing applications. Some of them have trivial root bpf program that only does multiple bpf_tail_calls and at init time the prog array is empty. In the future we may add a flag to do such tracking optionally, but for now play simple and safe. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
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