Patch SSL Certificate handling in mongodump 4.2+ (go lang)

I wish to upgrade my Mongo database from version 4 to 5. I use ssl configuration with Mongo to ensure communication with the database is encrypted. To backup the database I use mongodump.

In Mongo 4.2 mongodump was rewritten in Go lang, causing it to import a common Go bug around ssl certificate handling. Specifically PEM files with intermediate certificates aren't fully loaded. The bug does not impact Mongo server or client itself, any version, or any other apps. Only mongodump is impacted.

The bug is described here: https://jira.mongodb.org/browse/TOOLS-2598

> Since tool's SSL/TLS code is copied from Go driver, the current implementation only parses the last certificate inside the pem file

> This is a discrepancy with Mongoshell behavior, which only loads the first certificate inside the pem file.

In this related exchange: https://jira.mongodb.org/browse/TOOLS-2996 I fail to see the resolution. I have tried every permutation of keys and certificates in the arguments passed to mongodump.

I've been looking at the source code for mongodump and specifically the SSL loading code.

To aid in go development, I've created this dockerfile to instantly provide a working environment for building this code but I am unfamiliar with go as a language.

FROM centos:8
RUN yum -y update
RUN yum -y install git-core vim-enhanced golang krb5-devel krb5-libs snappy
RUN groupadd -r app -g 1000 && \
    useradd -r -g app -u 1000 app -d /app && \
    mkdir -p /app && \
    chown -R app:app /app
USER 1000
WORKDIR /app
ENTRYPOINT /bin/bash

How plausible is it to fix these PEM loading bugs in this code base? My Mongo estate has many clients so rotating the certificates to solve this issue involves a high degree of planning and downtime. Patching mongodump to accept the existing certs feels like an acceptable medium term trade off.

Is anyone able to help me write the appropriate patch, perhaps there's standard ssl code that go developers use now? Does anyone have any ideas on how I can move this forward please? (Patches would be ideal!)

I apologise in advance that I have no reproducible test case here due to complexities of how the certificates I want to test were created.

This patch I've written (based on a rejected git pull request for GODRIVER-1753) resolves the issues.

https://jira.mongodb.org/browse/GODRIVER-1753

https://github.com/mongodb/mongo-go-driver/pull/521/files

It also fixes an asn1 trailing data issue too.

diff --git a/README.md b/README.md
index 20f3ffe8..4b3bed1a 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,13 @@
+
+** PATCHED MONGO-TOOLS **
+
+In Mongo 4.2, the mongo team rewrote many of their core tools in Go.
+
+This introduced a bug with the way that PEM files are handled.
+Faced with downtime and complexity in a large Mongo estate, this
+patched version of mongo resolves the issues.
+
+
 MongoDB Tools
 ===================================
 
diff --git a/common/db/db.go b/common/db/db.go
index 3e78abab..9290bb31 100644
--- a/common/db/db.go
+++ b/common/db/db.go
@@ -186,9 +186,13 @@ func addClientCertFromBytes(cfg *tls.Config, data []byte, keyPasswd string) (str
                }
 
                if currentBlock.Type == "CERTIFICATE" {
-			certBlock = data[start : len(data)-len(remaining)]
-			certDecodedBlock = currentBlock.Bytes
-			start += len(certBlock)
+			tempCertBlock := data[start : len(data)-len(remaining)]
+			certBlock = append(certBlock, tempCertBlock...) //To handle usecase where multiple certs are present
+
+			tempCertEncodedBlock := currentBlock.Bytes
+			certDecodedBlock = append(certDecodedBlock, tempCertEncodedBlock...)
+
+			start += len(tempCertBlock)
                } else if strings.HasSuffix(currentBlock.Type, "PRIVATE KEY") {
                        isEncrypted := x509.IsEncryptedPEMBlock(currentBlock) || strings.Contains(currentBlock.Type, "ENCRYPTED PRIVATE KEY")
                        if isEncrypted {
@@ -244,12 +248,17 @@ func addClientCertFromBytes(cfg *tls.Config, data []byte, keyPasswd string) (str
 
        // The documentation for the tls.X509KeyPair indicates that the Leaf certificate is not
        // retained.
-	crt, err := x509.ParseCertificate(certDecodedBlock)
-	if err != nil {
-		return "", err
-	}
-
-	return crt.Subject.String(), nil
+        l := len(certDecodedBlock)
+        for {
+          crt, err := x509.ParseCertificate(certDecodedBlock[0:l])
+          if err == nil {
+            return crt.Subject.String(), nil
+          }
+          l = l - 1
+          if l == 0 {
+            return "", err
+          }
+        }
 }
 
 // create a username for x509 authentication from an x509 certificate subject.
diff --git a/vendor/go.mongodb.org/mongo-driver/mongo/options/clientoptions.go b/vendor/go.mongodb.org/mongo-driver/mongo/options/clientoptions.go
index d66114fa..2f3c6554 100644
--- a/vendor/go.mongodb.org/mongo-driver/mongo/options/clientoptions.go
+++ b/vendor/go.mongodb.org/mongo-driver/mongo/options/clientoptions.go
@@ -941,9 +941,13 @@ func addClientCertFromBytes(cfg *tls.Config, data []byte, keyPasswd string) (str
                }
 
                if currentBlock.Type == "CERTIFICATE" {
-			certBlock = data[start : len(data)-len(remaining)]
-			certDecodedBlock = currentBlock.Bytes
-			start += len(certBlock)
+			tempCertBlock := data[start : len(data)-len(remaining)]
+			certBlock = append(certBlock, tempCertBlock...) //To handle usecase where multiple certs are present
+
+			tempCertEncodedBlock := currentBlock.Bytes
+			certDecodedBlock = append(certDecodedBlock, tempCertEncodedBlock...)
+
+			start += len(tempCertBlock)
                } else if strings.HasSuffix(currentBlock.Type, "PRIVATE KEY") {
                        isEncrypted := x509.IsEncryptedPEMBlock(currentBlock) || strings.Contains(currentBlock.Type, "ENCRYPTED PRIVATE KEY")
                        if isEncrypted {
@@ -997,12 +1001,18 @@ func addClientCertFromBytes(cfg *tls.Config, data []byte, keyPasswd string) (str
 
        // The documentation for the tls.X509KeyPair indicates that the Leaf certificate is not
        // retained.
-	crt, err := x509.ParseCertificate(certDecodedBlock)
-	if err != nil {
-		return "", err
-	}
+        l := len(certDecodedBlock)
+        for {
+          crt, err := x509.ParseCertificate(certDecodedBlock[0:l])
+          if err == nil {
+            return crt.Subject.String(), nil
+          }
+          l = l - 1
+          if l == 0 {
+            return "", err
+          }
+        }
 
-	return x509CertSubject(crt), nil
 }
 
 func stringSliceContains(source []string, target string) bool {