bpf: Move getsockopt retval to struct bpf_cg_run_ctx
The retval value is moved to struct bpf_cg_run_ctx for ease of access in different prog types with different context structs layouts. The helper implementation (to be added in a later patch in the series) can simply perform a container_of from current->bpf_ctx to retrieve bpf_cg_run_ctx. Unfortunately, there is no easy way to access the current task_struct via the verifier BPF bytecode rewrite, aside from possibly calling a helper, so a pointer to current task is added to struct bpf_sockopt_kern so that the rewritten BPF bytecode can access struct bpf_cg_run_ctx with an indirection. For backward compatibility, if a getsockopt program rejects a syscall by returning 0, an -EPERM will be generated, by having the BPF_PROG_RUN_ARRAY_CG family macros automatically set the retval to -EPERM. Unlike prior to this patch, this -EPERM will be visible to ctx->retval for any other hooks down the line in the prog array. Additionally, the restriction that getsockopt filters can only set the retval to 0 is removed, considering that certain getsockopt implementations may return optlen. Filters are now able to set the value arbitrarily. Signed-off-by: YiFei Zhu <zhuyifei@google.com> Reviewed-by: Stanislav Fomichev <sdf@google.com> Link: https://lore.kernel.org/r/73b0325f5c29912ccea7ea57ec1ed4d388fc1d37.1639619851.git.zhuyifei@google.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>
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