fix(sse): document and lock anonymous denial under KMS key policy (#6739)

crates/e2e_test/src/kms/kms_anonymous_enforcement_test.rs

@@ -0,0 +1,220 @@
+// Copyright 2024 RustFS Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Anonymous access to SSE-KMS objects under per-key authorization.
+//!
+//! Locks both halves of the anonymous contract decided in backlog#2028 (D4):
+//!
+//! - **Enforcement on**: anonymous requests hold no `kms` grants, so a public
+//!   bucket policy does not let them read SSE-KMS objects or write through an
+//!   SSE-KMS default-encryption rule. Both fail with `AccessDenied`.
+//! - **Enforcement off** (the default): bucket policy alone governs anonymous
+//!   access, matching the pre-enforcement behavior — public SSE-KMS objects are
+//!   decrypted and served, and anonymous writes are encrypted under the default
+//!   key.
+//!
+//! The denial today is emergent — an empty-account principal falling through to
+//! the IAM default deny — so without this file a refactor of principal
+//! construction or policy evaluation could silently flip it. Each test carries a
+//! plaintext-object positive control: a denial proves nothing while the bucket
+//! policy has not propagated.
+
+use super::common::{LocalKMSTestEnvironment, create_key_with_specific_id};
+use crate::common::{init_logging, local_http_client};
+use aws_sdk_s3::primitives::ByteStream;
+use aws_sdk_s3::types::{
+    ServerSideEncryption, ServerSideEncryptionByDefault, ServerSideEncryptionConfiguration, ServerSideEncryptionRule,
+};
+use std::time::Duration;
+
+type TestResult = Result<(), Box<dyn std::error::Error + Send + Sync>>;
+
+const DEFAULT_KEY: &str = "kms-anon-default-key";
+const BUCKET: &str = "kms-anon-enforcement";
+const PLAIN_OBJECT: &str = "plain.txt";
+const ENCRYPTED_OBJECT: &str = "encrypted.txt";
+const PAYLOAD: &[u8] = b"kms anonymous enforcement payload";
+
+/// How long a bucket policy change may take to reach the request path.
+const POLICY_PROPAGATION: Duration = Duration::from_secs(20);
+
+/// Start a local-KMS server and build the public-bucket fixture.
+///
+/// The bucket holds a plaintext object (the positive control), an SSE-KMS
+/// object, an SSE-KMS default-encryption rule, and a bucket policy opening
+/// `GetObject`/`PutObject` to everyone. The enforcement switch defaults to off,
+/// so the enforcing case has to set it explicitly.
+async fn start_public_sse_kms_bucket(env: &mut LocalKMSTestEnvironment, enforce: bool) -> TestResult {
+    create_key_with_specific_id(&env.kms_keys_dir, DEFAULT_KEY).await?;
+
+    let key_dir = env.kms_keys_dir.clone();
+    let args = vec![
+        "--kms-enable",
+        "--kms-backend",
+        "local",
+        "--kms-key-dir",
+        key_dir.as_str(),
+        "--kms-default-key-id",
+        DEFAULT_KEY,
+    ];
+    let mut envs = vec![("RUSTFS_KMS_ALLOW_INSECURE_DEV_DEFAULTS", "true")];
+    if enforce {
+        envs.push(("RUSTFS_KMS_ENFORCE_SSE_KEY_POLICY", "true"));
+    }
+    env.base_env.start_rustfs_server_with_env(args, &envs).await?;
+    env.base_env.create_test_bucket(BUCKET).await?;
+
+    let owner = env.base_env.create_s3_client();
+
+    owner
+        .put_object()
+        .bucket(BUCKET)
+        .key(PLAIN_OBJECT)
+        .body(ByteStream::from_static(PAYLOAD))
+        .send()
+        .await?;
+    owner
+        .put_object()
+        .bucket(BUCKET)
+        .key(ENCRYPTED_OBJECT)
+        .body(ByteStream::from_static(PAYLOAD))
+        .server_side_encryption(ServerSideEncryption::AwsKms)
+        .ssekms_key_id(DEFAULT_KEY)
+        .send()
+        .await?;
+
+    let encryption_config = ServerSideEncryptionConfiguration::builder()
+        .rules(
+            ServerSideEncryptionRule::builder()
+                .apply_server_side_encryption_by_default(
+                    ServerSideEncryptionByDefault::builder()
+                        .sse_algorithm(ServerSideEncryption::AwsKms)
+                        .kms_master_key_id(DEFAULT_KEY)
+                        .build()?,
+                )
+                .build(),
+        )
+        .build()?;
+    owner
+        .put_bucket_encryption()
+        .bucket(BUCKET)
+        .server_side_encryption_configuration(encryption_config)
+        .send()
+        .await?;
+
+    let policy = serde_json::json!({
+        "Version": "2012-10-17",
+        "Statement": [{
+            "Sid": "PublicReadWrite",
+            "Effect": "Allow",
+            "Principal": "*",
+            "Action": ["s3:GetObject", "s3:PutObject"],
+            "Resource": [format!("arn:aws:s3:::{BUCKET}/*")]
+        }]
+    })
+    .to_string();
+    owner.put_bucket_policy().bucket(BUCKET).policy(&policy).send().await?;
+    let _ = owner.delete_public_access_block().bucket(BUCKET).send().await;
+
+    Ok(())
+}
+
+fn object_url(env: &LocalKMSTestEnvironment, key: &str) -> String {
+    format!("{}/{BUCKET}/{key}", env.base_env.url)
+}
+
+async fn anonymous_get(env: &LocalKMSTestEnvironment, key: &str) -> Result<reqwest::Response, reqwest::Error> {
+    local_http_client().get(object_url(env, key)).send().await
+}
+
+async fn anonymous_put(env: &LocalKMSTestEnvironment, key: &str) -> Result<reqwest::Response, reqwest::Error> {
+    local_http_client().put(object_url(env, key)).body(PAYLOAD).send().await
+}
+
+/// Retry the plaintext read until the public bucket policy is live.
+async fn wait_for_public_read(env: &LocalKMSTestEnvironment) -> TestResult {
+    let deadline = tokio::time::Instant::now() + POLICY_PROPAGATION;
+    loop {
+        let status = anonymous_get(env, PLAIN_OBJECT).await?.status();
+        if status.as_u16() == 200 {
+            return Ok(());
+        }
+        if tokio::time::Instant::now() >= deadline {
+            return Err(format!("positive control never became readable: anonymous GET {PLAIN_OBJECT} -> {status}").into());
+        }
+        tokio::time::sleep(Duration::from_millis(500)).await;
+    }
+}
+
+async fn assert_anonymous_denied(response: reqwest::Response, what: &str) -> TestResult {
+    let status = response.status().as_u16();
+    let body = response.text().await?;
+    assert_eq!(status, 403, "{what} must be denied, got {status}: {body}");
+    assert!(body.contains("AccessDenied"), "{what} must carry AccessDenied: {body}");
+    Ok(())
+}
+
+/// Enforcement on: a public bucket policy does not exempt anonymous requests
+/// from per-key authorization, on either the read or the default-encryption
+/// write path.
+#[tokio::test(flavor = "multi_thread")]
+async fn anonymous_sse_kms_denied_under_enforcement() -> TestResult {
+    init_logging();
+
+    let mut env = LocalKMSTestEnvironment::new().await?;
+    start_public_sse_kms_bucket(&mut env, true).await?;
+    wait_for_public_read(&env).await?;
+
+    let read = anonymous_get(&env, ENCRYPTED_OBJECT).await?;
+    assert_anonymous_denied(read, "anonymous GET of an SSE-KMS object").await?;
+
+    let write = anonymous_put(&env, "anon-write.txt").await?;
+    assert_anonymous_denied(write, "anonymous PUT through an SSE-KMS default-encryption rule").await?;
+
+    Ok(())
+}
+
+/// Enforcement off (the default): bucket policy alone governs anonymous access,
+/// and the default-encryption rule still encrypts anonymous writes.
+#[tokio::test(flavor = "multi_thread")]
+async fn anonymous_sse_kms_governed_by_bucket_policy_without_enforcement() -> TestResult {
+    init_logging();
+
+    let mut env = LocalKMSTestEnvironment::new().await?;
+    start_public_sse_kms_bucket(&mut env, false).await?;
+    wait_for_public_read(&env).await?;
+
+    let read = anonymous_get(&env, ENCRYPTED_OBJECT).await?;
+    assert_eq!(read.status().as_u16(), 200, "anonymous GET of a public SSE-KMS object must succeed");
+    assert_eq!(read.bytes().await?.as_ref(), PAYLOAD, "the object must be served decrypted");
+
+    let write = anonymous_put(&env, "anon-write.txt").await?;
+    assert_eq!(write.status().as_u16(), 200, "anonymous PUT to a public bucket must succeed");
+
+    let stored = env
+        .base_env
+        .create_s3_client()
+        .head_object()
+        .bucket(BUCKET)
+        .key("anon-write.txt")
+        .send()
+        .await?;
+    assert_eq!(
+        stored.server_side_encryption(),
+        Some(&ServerSideEncryption::AwsKms),
+        "the anonymous write must be encrypted by the bucket default rule"
+    );
+
+    Ok(())
+}

crates/e2e_test/src/kms/mod.rs

@@ -57,6 +57,9 @@ mod copy_object_version_restore_sse_test;
 #[cfg(test)]
 mod configured_roundtrip_test;
 
+#[cfg(test)]
+mod kms_anonymous_enforcement_test;
+
 #[cfg(test)]
 mod kms_authorization_negative_matrix_test;