s3api: verify signed request bodies against the signed payload hash (#12577)

* s3api: verify signed request bodies against the signed payload hash

A SigV4 signature covers the declared x-amz-content-sha256, but only
getRequestDataReader (PutObject, UploadPart) compared the body with it.
Every other handler parsed the body as received, so a signed request,
DeleteObjects for example, could be replayed with a different body.

After a V4 signature verifies, wrap the body so it is handed out only
once all of it has been read and matched against the hash the signature
covered; a decoder that stops reading early never sees unverified bytes.
getRequestDataReader unwraps it and keeps verifying uploads as they
stream.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* s3api: answer XAmzContentSHA256Mismatch for refused DeleteObjects bodies

DeleteObjects answered a body that failed its payload-hash check with
InternalError and CompleteMultipartUpload with MalformedXML. Name the
check that failed instead, as PutObject does.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* s3api: check Content-MD5 on signed request bodies

Signature V2 signs Content-MD5 rather than a payload hash, and a V4
request sent with UNSIGNED-PAYLOAD may still sign it, but bodies read
outside the upload path never compared it with the body. Check it with
the payload hash once a V2 or V4 signature verifies: BadDigest on a
mismatch, InvalidDigest when it is malformed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* s3api: verify presigned uploads against a signed payload hash

A presigned V4 URL can sign X-Amz-Content-Sha256 as a query parameter,
but getRequestDataReader compared upload bodies only with the header of
that name, so the signed hash went unchecked. Verify uploads against the
hash the signature covered.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* s3api: check Content-MD5 on bodies buffered for their payload hash

IAM and other non-S3 requests signed without x-amz-content-sha256 have
their body buffered and hashed during signature verification. That
buffer counted as already bound, so their Content-MD5 was never checked.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* s3api: check Content-MD5 on directory marker bodies

A PUT of a key ending in "/" stores its body on the directory entry
without going through putToFiler, so its Content-MD5 was never compared
with the body. Answer BadDigest on a mismatch, as putToFiler does.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* s3api: wrap and unwrap signed bodies through helpers

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

weed/s3api/s3api_storage_class_validation_test.go

@@ -230,6 +230,23 @@ func TestPutObjectDirectoryMarkerStoresHeaders(t *testing.T) {
 	require.ElementsMatch(t, []Tag{{Key: "k1", Value: "v1"}, {Key: "k2", Value: "v2"}}, tagging.TagSet.Tag)
 }
 
+func TestPutObjectDirectoryMarkerChecksContentMd5(t *testing.T) {
+	s3a, filer, _ := newHeaderTestServer(t, "")
+	req, probe := newHeaderTestRequest("/b/dir/", "dir/", "marker", "Content-Md5", getMD5HashBase64([]byte("other")))
+
+	s3a.PutObjectHandler(probe, req)
+
+	require.Equal(t, http.StatusBadRequest, probe.Code, probe.Body.String())
+	require.Contains(t, probe.Body.String(), "BadDigest")
+	filer.mu.Lock()
+	require.Nil(t, filer.entries["/buckets/b/dir"], "directory marker created")
+	filer.mu.Unlock()
+
+	req, probe = newHeaderTestRequest("/b/dir/", "dir/", "marker", "Content-Md5", getMD5HashBase64([]byte("marker")))
+	s3a.PutObjectHandler(probe, req)
+	require.Equal(t, http.StatusOK, probe.Code, probe.Body.String())
+}
+
 // A valid storage class still stores, and the content type is still sniffed.
 func TestPutObjectValidStorageClassSniffsContentType(t *testing.T) {
 	s3a, filer, volume := newHeaderTestServer(t, "")