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Commitd0206e7

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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 commitd0206e7

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6 files changed

+227
-17
lines changed

6 files changed

+227
-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:=WorkspaceKeySeed(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+
// WorkspaceKeySeed converts a WorkspaceID UUID and agent name to an int64 hash.
1875+
// This uses the FNV-1a hash algorithm which provides decent distribution and collision
1876+
// resistance for string inputs.
1877+
funcWorkspaceKeySeed(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: 108 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -3,11 +3,12 @@ package agentssh
33
import (
44
"bufio"
55
"context"
6-
"crypto/rand"
76
"crypto/rsa"
87
"errors"
98
"fmt"
109
"io"
10+
"math/big"
11+
"math/rand"
1112
"net"
1213
"os"
1314
"os/exec"
@@ -128,17 +129,6 @@ type Server struct {
128129
}
129130

130131
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-
}
142132
ifconfig==nil {
143133
config=&Config{}
144134
}
@@ -205,8 +195,10 @@ func NewServer(ctx context.Context, logger slog.Logger, prometheusRegistry *prom
205195
slog.F("local_addr",conn.LocalAddr()),
206196
slog.Error(err))
207197
},
208-
Handler:s.sessionHandler,
209-
HostSigners: []ssh.Signer{randomSigner},
198+
Handler:s.sessionHandler,
199+
// HostSigners are intentionally empty, as the host key will
200+
// be set before we start listening.
201+
HostSigners: []ssh.Signer{},
210202
LocalPortForwardingCallback:func(ctx ssh.Context,destinationHoststring,destinationPortuint32)bool {
211203
// Allow local port forwarding all!
212204
s.logger.Debug(ctx,"local port forward",
@@ -844,7 +836,13 @@ func (s *Server) CreateCommand(ctx context.Context, script string, env []string,
844836
returncmd,nil
845837
}
846838

839+
// Serve starts the server to handle incoming connections on the provided listener.
840+
// It returns an error if no host keys are set or if there is an issue accepting connections.
847841
func (s*Server)Serve(l net.Listener) (retErrerror) {
842+
iflen(s.srv.HostSigners)==0 {
843+
returnxerrors.New("no host keys set")
844+
}
845+
848846
s.logger.Info(context.Background(),"started serving listener",slog.F("listen_addr",l.Addr()))
849847
deferfunc() {
850848
s.logger.Info(context.Background(),"stopped serving listener",
@@ -1099,3 +1097,99 @@ func userHomeDir() (string, error) {
10991097
}
11001098
returnu.HomeDir,nil
11011099
}
1100+
1101+
// UpdateHostSigner updates the host signer with a new key generated from the provided seed.
1102+
// If an existing host key exists with the same algorithm, it is overwritten
1103+
func (s*Server)UpdateHostSigner(seedint64)error {
1104+
key,err:=CoderSigner(seed)
1105+
iferr!=nil {
1106+
returnerr
1107+
}
1108+
1109+
s.mu.Lock()
1110+
defers.mu.Unlock()
1111+
1112+
s.srv.AddHostKey(key)
1113+
1114+
returnnil
1115+
}
1116+
1117+
// CoderSigner generates a deterministic SSH signer based on the provided seed.
1118+
// It uses RSA with a key size of 2048 bits.
1119+
funcCoderSigner(seedint64) (gossh.Signer,error) {
1120+
// Clients should ignore the host key when connecting.
1121+
// The agent needs to authenticate with coderd to SSH,
1122+
// so SSH authentication doesn't improve security.
1123+
1124+
// Since the standard lib purposefully does not generate
1125+
// deterministic rsa keys, we need to do it ourselves.
1126+
coderHostKey:=func()*rsa.PrivateKey {
1127+
// Create deterministic random source
1128+
// nolint: gosec
1129+
deterministicRand:=rand.New(rand.NewSource(seed))
1130+
1131+
// Use fixed values for p and q based on the seed
1132+
p:=big.NewInt(0)
1133+
q:=big.NewInt(0)
1134+
e:=big.NewInt(65537)// Standard RSA public exponent
1135+
1136+
// Generate deterministic primes using the seeded random
1137+
// Each prime should be ~1024 bits to get a 2048-bit key
1138+
for {
1139+
p.SetBit(p,1024,1)// Ensure it's large enough
1140+
fori:=0;i<1024;i++ {
1141+
ifdeterministicRand.Int63()%2==1 {
1142+
p.SetBit(p,i,1)
1143+
}else {
1144+
p.SetBit(p,i,0)
1145+
}
1146+
}
1147+
ifp.ProbablyPrime(20) {
1148+
break
1149+
}
1150+
}
1151+
1152+
for {
1153+
q.SetBit(q,1024,1)// Ensure it's large enough
1154+
fori:=0;i<1024;i++ {
1155+
ifdeterministicRand.Int63()%2==1 {
1156+
q.SetBit(q,i,1)
1157+
}else {
1158+
q.SetBit(q,i,0)
1159+
}
1160+
}
1161+
ifq.ProbablyPrime(20)&&p.Cmp(q)!=0 {
1162+
break
1163+
}
1164+
}
1165+
1166+
// Calculate n = p * q
1167+
n:=new(big.Int).Mul(p,q)
1168+
1169+
// Calculate phi = (p-1) * (q-1)
1170+
p1:=new(big.Int).Sub(p,big.NewInt(1))
1171+
q1:=new(big.Int).Sub(q,big.NewInt(1))
1172+
phi:=new(big.Int).Mul(p1,q1)
1173+
1174+
// Calculate private exponent d
1175+
d:=new(big.Int).ModInverse(e,phi)
1176+
1177+
// Create the private key
1178+
privateKey:=&rsa.PrivateKey{
1179+
PublicKey: rsa.PublicKey{
1180+
N:n,
1181+
E:int(e.Int64()),
1182+
},
1183+
D:d,
1184+
Primes: []*big.Int{p,q},
1185+
}
1186+
1187+
// Compute precomputed values
1188+
privateKey.Precompute()
1189+
1190+
returnprivateKey
1191+
}()
1192+
1193+
coderSigner,err:=gossh.NewSignerFromKey(coderHostKey)
1194+
returncoderSigner,err
1195+
}

‎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)

‎cli/ssh_test.go‎

Lines changed: 66 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -453,6 +453,72 @@ func TestSSH(t *testing.T) {
453453
<-cmdDone
454454
})
455455

456+
t.Run("DeterministicHostKey",func(t*testing.T) {
457+
t.Parallel()
458+
client,workspace,agentToken:=setupWorkspaceForAgent(t)
459+
_,_=tGoContext(t,func(ctx context.Context) {
460+
// Run this async so the SSH command has to wait for
461+
// the build and agent to connect!
462+
_=agenttest.New(t,client.URL,agentToken)
463+
<-ctx.Done()
464+
})
465+
466+
clientOutput,clientInput:=io.Pipe()
467+
serverOutput,serverInput:=io.Pipe()
468+
deferfunc() {
469+
for_,c:=range []io.Closer{clientOutput,clientInput,serverOutput,serverInput} {
470+
_=c.Close()
471+
}
472+
}()
473+
474+
ctx,cancel:=context.WithTimeout(context.Background(),testutil.WaitLong)
475+
defercancel()
476+
477+
inv,root:=clitest.New(t,"ssh","--stdio",workspace.Name)
478+
clitest.SetupConfig(t,client,root)
479+
inv.Stdin=clientOutput
480+
inv.Stdout=serverInput
481+
inv.Stderr=io.Discard
482+
483+
cmdDone:=tGo(t,func() {
484+
err:=inv.WithContext(ctx).Run()
485+
assert.NoError(t,err)
486+
})
487+
488+
keySeed,err:=agent.WorkspaceKeySeed(workspace.ID,"dev")
489+
assert.NoError(t,err)
490+
491+
signer,err:=agentssh.CoderSigner(keySeed)
492+
assert.NoError(t,err)
493+
494+
conn,channels,requests,err:=ssh.NewClientConn(&stdioConn{
495+
Reader:serverOutput,
496+
Writer:clientInput,
497+
},"",&ssh.ClientConfig{
498+
// #nosec
499+
HostKeyCallback:ssh.FixedHostKey(signer.PublicKey()),
500+
})
501+
require.NoError(t,err)
502+
deferconn.Close()
503+
504+
sshClient:=ssh.NewClient(conn,channels,requests)
505+
session,err:=sshClient.NewSession()
506+
require.NoError(t,err)
507+
defersession.Close()
508+
509+
command:="sh -c exit"
510+
ifruntime.GOOS=="windows" {
511+
command="cmd.exe /c exit"
512+
}
513+
err=session.Run(command)
514+
require.NoError(t,err)
515+
err=sshClient.Close()
516+
require.NoError(t,err)
517+
_=clientOutput.Close()
518+
519+
<-cmdDone
520+
})
521+
456522
t.Run("NetworkInfo",func(t*testing.T) {
457523
t.Parallel()
458524
client,workspace,agentToken:=setupWorkspaceForAgent(t)

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