reduce the chance of parsing /etc/passwd & /etc/group

[lifubang]

According to #3998 (comment), we can do the third step to reduce the chance of parsing /etc/passwd & /etc/group when start or exec to a container.

Because in runtime-spec(https://github.com/opencontainers/runtime-spec/blob/v1.0.2/config.md#posix-platform-user), uid, gid, and additionalGids are all defined as a numeric field/array. It is no need to parse a numeric id from /etc/passwd or /etc/group, except $HOME is empty or gid is not provided(But runtime-spec said gid is required).

[kolyshkin]

The number to string to number conversion is ugly.

I think we should do a change like this:

@@ -68,8 +68,9 @@ type initConfig struct {
        ProcessLabel     string                `json:"process_label"`
        AppArmorProfile  string                `json:"apparmor_profile"`
        NoNewPrivileges  bool                  `json:"no_new_privileges"`
-       User             string                `json:"user"`
-       AdditionalGroups []string              `json:"additional_groups"`
+       UID              int                   `json:"uid"`
+       GID              int                   `json:"gid"`
+       AdditionalGroups []int                 `json:"additional_groups"`
        Config           *configs.Config       `json:"config"`
        Networks         []*network            `json:"network"`
        PassedFilesCount int                   `json:"passed_files_count"`

and the rest will be greatly simplified.

[kolyshkin]

I think we should do a change like this:

and the same for Process struct:

        // Env specifies the environment variables for the process.
        Env []string
 
-       // User will set the uid and gid of the executing process running inside the container
+       // UID and GID of the executing process running inside the container
        // local to the container's user and group configuration.
-       User string
+       UID, GID int
 
        // AdditionalGroups specifies the gids that should be added to supplementary groups
        // in addition to those that the user belongs to.
-       AdditionalGroups []string
+       AdditionalGroups []int
 
        // Cwd will change the processes current working directory inside the container's rootfs.
        Cwd string

[kolyshkin]

In fact, I forgot I had the code doing all that already. Rebased it, PTAL: #3999

[lifubang]

OK, thanks, leave one to save our reviewing time.