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Commit9c85cde

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committed
fix(agent/agentssh): pin random seed for RSA key generation
Change-Id: I8c7e3070324e5d558374fd6891eea9d48660e1e9Signed-off-by: Thomas Kosiewski <tk@coder.com>
1 parent4449931 commit9c85cde

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5 files changed

+97
-17
lines changed

5 files changed

+97
-17
lines changed

‎agent/agent.go‎

Lines changed: 41 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -6,6 +6,7 @@ import (
66
"encoding/json"
77
"errors"
88
"fmt"
9+
"hash/fnv"
910
"io"
1011
"net/http"
1112
"net/netip"
@@ -994,7 +995,6 @@ func (a *agent) createOrUpdateNetwork(manifestOK, networkOK *checkpoint) func(co
994995
iferr:=manifestOK.wait(ctx);err!=nil {
995996
returnxerrors.Errorf("no manifest: %w",err)
996997
}
997-
varerrerror
998998
deferfunc() {
999999
networkOK.complete(retErr)
10001000
}()
@@ -1003,9 +1003,20 @@ func (a *agent) createOrUpdateNetwork(manifestOK, networkOK *checkpoint) func(co
10031003
network:=a.network
10041004
a.closeMutex.Unlock()
10051005
ifnetwork==nil {
1006+
keySeed,err:=workspaceSeed(manifest.WorkspaceID,manifest.AgentName)
1007+
iferr!=nil {
1008+
returnxerrors.Errorf("generate seed from workspace id: %w",err)
1009+
}
10061010
// use the graceful context here, because creating the tailnet is not itself tied to the
10071011
// agent API.
1008-
network,err=a.createTailnet(a.gracefulCtx,manifest.AgentID,manifest.DERPMap,manifest.DERPForceWebSockets,manifest.DisableDirectConnections)
1012+
network,err=a.createTailnet(
1013+
a.gracefulCtx,
1014+
manifest.AgentID,
1015+
manifest.DERPMap,
1016+
manifest.DERPForceWebSockets,
1017+
manifest.DisableDirectConnections,
1018+
keySeed,
1019+
)
10091020
iferr!=nil {
10101021
returnxerrors.Errorf("create tailnet: %w",err)
10111022
}
@@ -1145,7 +1156,13 @@ func (a *agent) trackGoroutine(fn func()) error {
11451156
returnnil
11461157
}
11471158

1148-
func (a*agent)createTailnet(ctx context.Context,agentID uuid.UUID,derpMap*tailcfg.DERPMap,derpForceWebSockets,disableDirectConnectionsbool) (_*tailnet.Conn,errerror) {
1159+
func (a*agent)createTailnet(
1160+
ctx context.Context,
1161+
agentID uuid.UUID,
1162+
derpMap*tailcfg.DERPMap,
1163+
derpForceWebSockets,disableDirectConnectionsbool,
1164+
keySeedint64,
1165+
) (_*tailnet.Conn,errerror) {
11491166
// Inject `CODER_AGENT_HEADER` into the DERP header.
11501167
varheader http.Header
11511168
ifclient,ok:=a.client.(*agentsdk.Client);ok {
@@ -1172,6 +1189,10 @@ func (a *agent) createTailnet(ctx context.Context, agentID uuid.UUID, derpMap *t
11721189
}
11731190
}()
11741191

1192+
iferr:=a.sshServer.UpdateHostSigner(keySeed);err!=nil {
1193+
returnnil,xerrors.Errorf("update host signer: %w",err)
1194+
}
1195+
11751196
sshListener,err:=network.Listen("tcp",":"+strconv.Itoa(workspacesdk.AgentSSHPort))
11761197
iferr!=nil {
11771198
returnnil,xerrors.Errorf("listen on the ssh port: %w",err)
@@ -1849,3 +1870,20 @@ func PrometheusMetricsHandler(prometheusRegistry *prometheus.Registry, logger sl
18491870
}
18501871
})
18511872
}
1873+
1874+
// workspaceSeed converts a WorkspaceID UUID to an int64 hash.
1875+
// This uses the FNV-1a hash algorithm which provides decent distribution and collision
1876+
// resistance for string inputs.
1877+
funcworkspaceSeed(workspaceID uuid.UUID,agentNamestring) (int64,error) {
1878+
h:=fnv.New64a()
1879+
_,err:=h.Write(workspaceID[:])
1880+
iferr!=nil {
1881+
return42,err
1882+
}
1883+
_,err=h.Write([]byte(agentName))
1884+
iferr!=nil {
1885+
return42,err
1886+
}
1887+
1888+
returnint64(h.Sum64()),nil
1889+
}

‎agent/agentssh/agentssh.go‎

Lines changed: 44 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -3,11 +3,11 @@ package agentssh
33
import (
44
"bufio"
55
"context"
6-
"crypto/rand"
76
"crypto/rsa"
87
"errors"
98
"fmt"
109
"io"
10+
"math/rand"
1111
"net"
1212
"os"
1313
"os/exec"
@@ -128,17 +128,6 @@ type Server struct {
128128
}
129129

130130
funcNewServer(ctx context.Context,logger slog.Logger,prometheusRegistry*prometheus.Registry,fs afero.Fs,execer agentexec.Execer,config*Config) (*Server,error) {
131-
// Clients' should ignore the host key when connecting.
132-
// The agent needs to authenticate with coderd to SSH,
133-
// so SSH authentication doesn't improve security.
134-
randomHostKey,err:=rsa.GenerateKey(rand.Reader,2048)
135-
iferr!=nil {
136-
returnnil,err
137-
}
138-
randomSigner,err:=gossh.NewSignerFromKey(randomHostKey)
139-
iferr!=nil {
140-
returnnil,err
141-
}
142131
ifconfig==nil {
143132
config=&Config{}
144133
}
@@ -205,8 +194,10 @@ func NewServer(ctx context.Context, logger slog.Logger, prometheusRegistry *prom
205194
slog.F("local_addr",conn.LocalAddr()),
206195
slog.Error(err))
207196
},
208-
Handler:s.sessionHandler,
209-
HostSigners: []ssh.Signer{randomSigner},
197+
Handler:s.sessionHandler,
198+
// HostSigners are intentionally empty, as the host key will
199+
// be set before we start listening.
200+
HostSigners: []ssh.Signer{},
210201
LocalPortForwardingCallback:func(ctx ssh.Context,destinationHoststring,destinationPortuint32)bool {
211202
// Allow local port forwarding all!
212203
s.logger.Debug(ctx,"local port forward",
@@ -844,7 +835,13 @@ func (s *Server) CreateCommand(ctx context.Context, script string, env []string,
844835
returncmd,nil
845836
}
846837

838+
// Serve starts the server to handle incoming connections on the provided listener.
839+
// It returns an error if no host keys are set or if there is an issue accepting connections.
847840
func (s*Server)Serve(l net.Listener) (retErrerror) {
841+
iflen(s.srv.HostSigners)==0 {
842+
returnxerrors.New("no host keys set")
843+
}
844+
848845
s.logger.Info(context.Background(),"started serving listener",slog.F("listen_addr",l.Addr()))
849846
deferfunc() {
850847
s.logger.Info(context.Background(),"stopped serving listener",
@@ -1099,3 +1096,36 @@ func userHomeDir() (string, error) {
10991096
}
11001097
returnu.HomeDir,nil
11011098
}
1099+
1100+
// UpdateHostSigner updates the host signer with a new key generated from the provided seed.
1101+
// If an existing host key exists with the same algorithm, it is overwritten
1102+
func (s*Server)UpdateHostSigner(seedint64)error {
1103+
key,err:=coderSigner(seed)
1104+
iferr!=nil {
1105+
returnerr
1106+
}
1107+
1108+
s.mu.Lock()
1109+
defers.mu.Unlock()
1110+
1111+
s.srv.AddHostKey(key)
1112+
1113+
returnnil
1114+
}
1115+
1116+
// coderSigner generates a deterministic SSH signer based on the provided seed.
1117+
// It uses RSA with a key size of 2048 bits.
1118+
funccoderSigner(seedint64) (gossh.Signer,error) {
1119+
// Clients should ignore the host key when connecting.
1120+
// The agent needs to authenticate with coderd to SSH,
1121+
// so SSH authentication doesn't improve security.
1122+
1123+
// nolint: gosec
1124+
deterministicRand:=rand.New(rand.NewSource(seed))
1125+
coderHostKey,err:=rsa.GenerateKey(deterministicRand,2048)
1126+
iferr!=nil {
1127+
returnnil,err
1128+
}
1129+
coderSigner,err:=gossh.NewSignerFromKey(coderHostKey)
1130+
returncoderSigner,err
1131+
}

‎agent/agentssh/agentssh_internal_test.go‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -39,6 +39,8 @@ func Test_sessionStart_orphan(t *testing.T) {
3939
s,err:=NewServer(ctx,logger,prometheus.NewRegistry(),afero.NewMemMapFs(),agentexec.DefaultExecer,nil)
4040
require.NoError(t,err)
4141
defers.Close()
42+
err=s.UpdateHostSigner(42)
43+
assert.NoError(t,err)
4244

4345
// Here we're going to call the handler directly with a faked SSH session
4446
// that just uses io.Pipes instead of a network socket. There is a large

‎agent/agentssh/agentssh_test.go‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -41,6 +41,8 @@ func TestNewServer_ServeClient(t *testing.T) {
4141
s,err:=agentssh.NewServer(ctx,logger,prometheus.NewRegistry(),afero.NewMemMapFs(),agentexec.DefaultExecer,nil)
4242
require.NoError(t,err)
4343
defers.Close()
44+
err=s.UpdateHostSigner(42)
45+
assert.NoError(t,err)
4446

4547
ln,err:=net.Listen("tcp","127.0.0.1:0")
4648
require.NoError(t,err)
@@ -146,6 +148,8 @@ func TestNewServer_CloseActiveConnections(t *testing.T) {
146148
s,err:=agentssh.NewServer(ctx,logger,prometheus.NewRegistry(),afero.NewMemMapFs(),agentexec.DefaultExecer,nil)
147149
require.NoError(t,err)
148150
defers.Close()
151+
err=s.UpdateHostSigner(42)
152+
assert.NoError(t,err)
149153

150154
ln,err:=net.Listen("tcp","127.0.0.1:0")
151155
require.NoError(t,err)
@@ -197,6 +201,8 @@ func TestNewServer_Signal(t *testing.T) {
197201
s,err:=agentssh.NewServer(ctx,logger,prometheus.NewRegistry(),afero.NewMemMapFs(),agentexec.DefaultExecer,nil)
198202
require.NoError(t,err)
199203
defers.Close()
204+
err=s.UpdateHostSigner(42)
205+
assert.NoError(t,err)
200206

201207
ln,err:=net.Listen("tcp","127.0.0.1:0")
202208
require.NoError(t,err)
@@ -262,6 +268,8 @@ func TestNewServer_Signal(t *testing.T) {
262268
s,err:=agentssh.NewServer(ctx,logger,prometheus.NewRegistry(),afero.NewMemMapFs(),agentexec.DefaultExecer,nil)
263269
require.NoError(t,err)
264270
defers.Close()
271+
err=s.UpdateHostSigner(42)
272+
assert.NoError(t,err)
265273

266274
ln,err:=net.Listen("tcp","127.0.0.1:0")
267275
require.NoError(t,err)

‎agent/agentssh/x11_test.go‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -38,6 +38,8 @@ func TestServer_X11(t *testing.T) {
3838
s,err:=agentssh.NewServer(ctx,logger,prometheus.NewRegistry(),fs,agentexec.DefaultExecer,&agentssh.Config{})
3939
require.NoError(t,err)
4040
defers.Close()
41+
err=s.UpdateHostSigner(42)
42+
assert.NoError(t,err)
4143

4244
ln,err:=net.Listen("tcp","127.0.0.1:0")
4345
require.NoError(t,err)

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