Fix race condition in server-mode

[masahiro331]

What did you implement:

I fixed the bug of race condition in vuls server-mode.

The server-mode runs report.NewDBClient only once the first time.
NewDBClient returns multiple DBs.

At this time, internally execute github.com/kotakanbe/go-cve-dictionary/db.NewDB which returns driver.
After this, The server-mode always execute functions such as NewOvalDB for the same driver .

This driver has the family property (e.g. d. Ovaldb).
After that, server-mode always executes functions like NewOvalDB for the same driver.
So, when a request from different OS is made asynchronously, ovaldb is rewritten.

This fix will generate a DB client for each request.

I added below log in goval-dictionary/db/redis.go.

func (d *RedisDriver) NewOvalDB(family string) error {
        fmt.Println("Call NewOvalDB")
        fmt.Printf("Pre NewOvalDB: %s\n", family)
        switch family {
        case c.CentOS:
                d.ovaldb = c.RedHat
        case c.Debian, c.Ubuntu, c.RedHat, c.Oracle,
                c.OpenSUSE, c.OpenSUSELeap, c.SUSEEnterpriseServer,
                c.SUSEEnterpriseDesktop, c.SUSEOpenstackCloud,
                c.Alpine, c.Amazon:

                d.ovaldb = family
        default:
                if strings.Contains(family, "suse") {
                        suses := []string{
                                c.OpenSUSE,
                                c.OpenSUSELeap,
                                c.SUSEEnterpriseServer,
                                c.SUSEEnterpriseDesktop,
                                c.SUSEOpenstackCloud,
                        }
                        return fmt.Errorf("Unknown SUSE. Specify from %s: %s", suses, family)
                }
                return fmt.Errorf("Unknown OS Type: %s", family)
        }
        fmt.Printf("Pro NewOvalDB: %s\n", family)
        return nil
}

Below execute log.

# First request after run the server-mode
Call NewOvalDB
Pre NewOvalDB: 
Pro NewOvalDB: redhat
・
・
・
# Second and subsequent requests after running server mode
Call NewOvalDB
Pre NewOvalDB: redhat
Pro NewOvalDB: ubuntu

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

I wrote PoC.
https://github.com/masahiro331/vuls_racecondition

I checked using PoC before and after the pull request.
Using DBs: Redis, Sqlite3 and postgresql.

Checklist:

• Write tests
• Write documentation
• Check that there aren't other open pull requests for the same issue/feature
• Format your source code by make fmt
• Pass the test by make test
• Provide verification config / commands
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: Yes

[kotakanbe]

Many Thanks!