From 10d262032cf458731a71cd0f0a9262b3a68cf73e Mon Sep 17 00:00:00 2001
From: Sunny <darkowlzz@protonmail.com>
Date: Thu, 28 Oct 2021 17:21:41 +0530
Subject: [PATCH] libgit2: handle EOF in parseKnownHosts()

parseKnownHosts() uses golang.org/x/crypto/ssh's ParseKnownHosts() for
parsing known hosts. It returns EOF error when the input is not a host
public key, but a valid known_hosts content, like a comment line.

With this fix, lines causing EOF error are skipped and the parsing of
the known_hosts file continues. But invalid lines still cause parsing
failure.

Signed-off-by: Sunny <darkowlzz@protonmail.com>
---
 pkg/git/libgit2/transport.go      |  6 +++
 pkg/git/libgit2/transport_test.go | 68 ++++++++++++++++++++++++++++++-
 2 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/pkg/git/libgit2/transport.go b/pkg/git/libgit2/transport.go
index 83d9107e..a15c725d 100644
--- a/pkg/git/libgit2/transport.go
+++ b/pkg/git/libgit2/transport.go
@@ -25,6 +25,7 @@ import (
 	"crypto/x509"
 	"fmt"
 	"hash"
+	"io"
 	"net"
 	"strings"
 	"time"
@@ -168,6 +169,11 @@ func parseKnownHosts(s string) ([]knownKey, error) {
 	for scanner.Scan() {
 		_, hosts, pubKey, _, _, err := ssh.ParseKnownHosts(scanner.Bytes())
 		if err != nil {
+			// Lines that aren't host public key result in EOF, like a comment
+			// line. Continue parsing the other lines.
+			if err == io.EOF {
+				continue
+			}
 			return []knownKey{}, err
 		}
 
diff --git a/pkg/git/libgit2/transport_test.go b/pkg/git/libgit2/transport_test.go
index 6f1e9545..15eb6400 100644
--- a/pkg/git/libgit2/transport_test.go
+++ b/pkg/git/libgit2/transport_test.go
@@ -251,7 +251,7 @@ func Test_knownHostsCallback(t *testing.T) {
 	}
 }
 
-func Test_parseKnownHosts(t *testing.T) {
+func Test_parseKnownHosts_matches(t *testing.T) {
 	tests := []struct {
 		name        string
 		hostkey     git2go.HostkeyCertificate
@@ -280,6 +280,72 @@ func Test_parseKnownHosts(t *testing.T) {
 	}
 }
 
+func Test_parseKnownHosts(t *testing.T) {
+	tests := []struct {
+		name    string
+		fixture string
+		wantErr bool
+	}{
+		{
+			name:    "empty file",
+			fixture: "",
+			wantErr: false,
+		},
+		{
+			name:    "single host",
+			fixture: `github.com ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAq2A7hRGmdnm9tUDbO9IDSwBK6TbQa+PXYPCPy6rbTrTtw7PHkccKrpp0yVhp5HdEIcKr6pLlVDBfOLX9QUsyCOV0wzfjIJNlGEYsdlLJizHhbn2mUjvSAHQqZETYP81eFzLQNnPHt4EVVUh7VfDESU84KezmD5QlWpXLmvU31/yMf+Se8xhHTvKSCZIFImWwoG6mbUoWf9nzpIoaSjB+weqqUUmpaaasXVal72J+UX2B+2RPW3RcT0eOzQgqlJL3RKrTJvdsjE3JEAvGq3lGHSZXy28G3skua2SmVi/w4yCE6gbODqnTWlg7+wC604ydGXA8VJiS5ap43JXiUFFAaQ==`,
+			wantErr: false,
+		},
+		{
+			name: "single host with comment",
+			fixture: `# github.com
+github.com ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAq2A7hRGmdnm9tUDbO9IDSwBK6TbQa+PXYPCPy6rbTrTtw7PHkccKrpp0yVhp5HdEIcKr6pLlVDBfOLX9QUsyCOV0wzfjIJNlGEYsdlLJizHhbn2mUjvSAHQqZETYP81eFzLQNnPHt4EVVUh7VfDESU84KezmD5QlWpXLmvU31/yMf+Se8xhHTvKSCZIFImWwoG6mbUoWf9nzpIoaSjB+weqqUUmpaaasXVal72J+UX2B+2RPW3RcT0eOzQgqlJL3RKrTJvdsjE3JEAvGq3lGHSZXy28G3skua2SmVi/w4yCE6gbODqnTWlg7+wC604ydGXA8VJiS5ap43JXiUFFAaQ==`,
+			wantErr: false,
+		},
+		{
+			name: "multiple hosts with comments",
+			fixture: `# github.com
+github.com ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAq2A7hRGmdnm9tUDbO9IDSwBK6TbQa+PXYPCPy6rbTrTtw7PHkccKrpp0yVhp5HdEIcKr6pLlVDBfOLX9QUsyCOV0wzfjIJNlGEYsdlLJizHhbn2mUjvSAHQqZETYP81eFzLQNnPHt4EVVUh7VfDESU84KezmD5QlWpXLmvU31/yMf+Se8xhHTvKSCZIFImWwoG6mbUoWf9nzpIoaSjB+weqqUUmpaaasXVal72J+UX2B+2RPW3RcT0eOzQgqlJL3RKrTJvdsjE3JEAvGq3lGHSZXy28G3skua2SmVi/w4yCE6gbODqnTWlg7+wC604ydGXA8VJiS5ap43JXiUFFAaQ==
+# gitlab.com
+gitlab.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAfuCHKVTjquxvt6CM6tdG4SLp1Btn/nOeHHE5UOzRdf`,
+		},
+		{
+			name: "no host key, only comments",
+			fixture: `# example.com
+#github.com
+# gitlab.com`,
+			wantErr: false,
+		},
+		{
+			name:    "invalid host entry",
+			fixture: `github.com ssh-rsa`,
+			wantErr: true,
+		},
+		{
+			name:    "invalid content",
+			fixture: `some random text`,
+			wantErr: true,
+		},
+		{
+			name: "invalid line with valid host key",
+			fixture: `some random text
+gitlab.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAfuCHKVTjquxvt6CM6tdG4SLp1Btn/nOeHHE5UOzRdf`,
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			g := NewWithT(t)
+			_, err := parseKnownHosts(tt.fixture)
+			if tt.wantErr {
+				g.Expect(err).To(HaveOccurred())
+			} else {
+				g.Expect(err).ToNot(HaveOccurred())
+			}
+		})
+	}
+}
+
 func md5Fingerprint(in string) [16]byte {
 	var out [16]byte
 	copy(out[:], in)