| 1 | package rootaws |
| 2 | |
| 3 | import ( |
| 4 | "log" |
| 5 | "os" |
| 6 | "strings" |
| 7 | ) |
| 8 | |
| 9 | // A child of a device cannot exist, even if a service user creates directories. |
| 10 | const disabledSharedFile = "/dev/null/carlos-root-aws" |
| 11 | |
| 12 | // rootScrubbedEnvironment names every variable that selects a file, a profile, |
| 13 | // an endpoint or a trust store the SDK would use on root's behalf. Root's own |
| 14 | // credentials come from the environment keys, the instance profile, or the |
| 15 | // validated off-cloud file, never from these. |
| 16 | var rootScrubbedEnvironment = []string{ |
| 17 | "AWS_CONFIG_FILE", |
| 18 | "AWS_SHARED_CREDENTIALS_FILE", |
| 19 | "AWS_PROFILE", |
| 20 | "AWS_DEFAULT_PROFILE", |
| 21 | "AWS_SDK_LOAD_CONFIG", |
| 22 | "AWS_CA_BUNDLE", |
| 23 | "AWS_WEB_IDENTITY_TOKEN_FILE", |
| 24 | "AWS_ROLE_ARN", |
| 25 | "AWS_ROLE_SESSION_NAME", |
| 26 | "AWS_CONTAINER_CREDENTIALS_FULL_URI", |
| 27 | "AWS_CONTAINER_CREDENTIALS_RELATIVE_URI", |
| 28 | "AWS_CONTAINER_AUTHORIZATION_TOKEN", |
| 29 | "AWS_CONTAINER_AUTHORIZATION_TOKEN_FILE", |
| 30 | "AWS_ENDPOINT_URL", |
| 31 | "AWS_EC2_METADATA_SERVICE_ENDPOINT", |
| 32 | "AWS_EC2_METADATA_SERVICE_ENDPOINT_MODE", |
| 33 | // Go's TLS trust store reads these unvalidated; AWS transports use it. |
| 34 | "SSL_CERT_FILE", |
| 35 | "SSL_CERT_DIR", |
| 36 | } |
| 37 | |
| 38 | // Service-specific endpoint overrides (AWS_ENDPOINT_URL_S3 and the rest) |
| 39 | // are matched by prefix. |
| 40 | const rootScrubbedEndpointPrefix = "AWS_ENDPOINT_URL_" |
| 41 | |
| 42 | // ScrubEnvironment must run before dispatch or goroutines in each executable. |
| 43 | // It also protects SDK loads in dependencies that do not call this package. |
| 44 | func ScrubEnvironment() { |
| 45 | scrubEnvironment(os.Geteuid()) |
| 46 | } |
| 47 | |
| 48 | func scrubEnvironment(euid int) { |
| 49 | if euid != 0 { |
| 50 | return |
| 51 | } |
| 52 | changed := false |
| 53 | keys := append([]string(nil), rootScrubbedEnvironment...) |
| 54 | for _, kv := range os.Environ() { |
| 55 | if key, _, _ := strings.Cut(kv, "="); strings.HasPrefix(key, rootScrubbedEndpointPrefix) { |
| 56 | keys = append(keys, key) |
| 57 | } |
| 58 | } |
| 59 | for _, key := range keys { |
| 60 | if value, set := os.LookupEnv(key); set && !inheritedSentinel(key, value) { |
| 61 | changed = true |
| 62 | } |
| 63 | _ = os.Unsetenv(key) |
| 64 | } |
| 65 | // A proxy may be needed off-cloud, so it stays, but it never answers for |
| 66 | // the instance metadata service: that is where root's EC2 credentials |
| 67 | // come from. |
| 68 | for _, key := range []string{"NO_PROXY", "no_proxy"} { |
| 69 | _ = os.Setenv(key, withIMDSBypass(os.Getenv(key))) |
| 70 | } |
| 71 | // Root never reads shared config, not even under its own HOME: a |
| 72 | // root-owned HOME can still hold a .aws the service user can write. |
| 73 | _ = os.Setenv("AWS_CONFIG_FILE", disabledSharedFile) |
| 74 | _ = os.Setenv("AWS_SHARED_CREDENTIALS_FILE", disabledSharedFile) |
| 75 | if changed { |
| 76 | log.Print("ALERT: root AWS file, profile, endpoint and trust-store environment overrides ignored") |
| 77 | } |
| 78 | } |
| 79 | |
| 80 | // inheritedSentinel reports a shared-file key that already holds the value |
| 81 | // this scrub sets: a root child of a scrubbed root parent inherits it, and |
| 82 | // that is not an override. Alerting on it would put the alert on the child's |
| 83 | // stderr, where a guarded updater reading `version` with combined output |
| 84 | // refuses the candidate. |
| 85 | func inheritedSentinel(key, value string) bool { |
| 86 | return (key == "AWS_CONFIG_FILE" || key == "AWS_SHARED_CREDENTIALS_FILE") && value == disabledSharedFile |
| 87 | } |
| 88 | |
| 89 | // imdsHosts are the IPv4 and IPv6 instance metadata addresses. |
| 90 | var imdsHosts = []string{"169.254.169.254", "fd00:ec2::254"} |
| 91 | |
| 92 | func withIMDSBypass(noProxy string) string { |
| 93 | entries := strings.FieldsFunc(noProxy, func(r rune) bool { return r == ',' }) |
| 94 | for _, host := range imdsHosts { |
| 95 | found := false |
| 96 | for _, entry := range entries { |
| 97 | if strings.TrimSpace(entry) == host { |
| 98 | found = true |
| 99 | } |
| 100 | } |
| 101 | if !found { |
| 102 | entries = append(entries, host) |
| 103 | } |
| 104 | } |
| 105 | return strings.Join(entries, ",") |
| 106 | } |
| 107 | |
amadan