1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
|
package sshd
import (
"context"
"errors"
"net"
"strings"
"time"
"github.com/sirupsen/logrus"
"golang.org/x/crypto/ssh"
"golang.org/x/sync/semaphore"
grpccodes "google.golang.org/grpc/codes"
grpcstatus "google.golang.org/grpc/status"
"gitlab.com/gitlab-org/gitlab-shell/v14/client"
"gitlab.com/gitlab-org/gitlab-shell/v14/internal/command/shared/disallowedcommand"
"gitlab.com/gitlab-org/gitlab-shell/v14/internal/config"
"gitlab.com/gitlab-org/gitlab-shell/v14/internal/metrics"
"gitlab.com/gitlab-org/labkit/log"
)
const (
KeepAliveMsg = "keepalive@openssh.com"
NotOurRefError = `exit status 128, stderr: "fatal: git upload-pack: not our ref `
)
var EOFTimeout = 10 * time.Second
type connection struct {
cfg *config.Config
concurrentSessions *semaphore.Weighted
nconn net.Conn
maxSessions int64
remoteAddr string
}
type channelHandler func(context.Context, *ssh.ServerConn, ssh.Channel, <-chan *ssh.Request) error
func newConnection(cfg *config.Config, nconn net.Conn) *connection {
maxSessions := cfg.Server.ConcurrentSessionsLimit
return &connection{
cfg: cfg,
maxSessions: maxSessions,
concurrentSessions: semaphore.NewWeighted(maxSessions),
nconn: nconn,
remoteAddr: nconn.RemoteAddr().String(),
}
}
func (c *connection) handle(ctx context.Context, srvCfg *ssh.ServerConfig, handler channelHandler) {
log.WithContextFields(ctx, log.Fields{}).Info("server: handleConn: start")
sconn, chans, err := c.initServerConn(ctx, srvCfg)
if err != nil {
return
}
if c.cfg.Server.ClientAliveInterval > 0 {
ticker := time.NewTicker(time.Duration(c.cfg.Server.ClientAliveInterval))
defer ticker.Stop()
go c.sendKeepAliveMsg(ctx, sconn, ticker)
}
c.handleRequests(ctx, sconn, chans, handler)
reason := sconn.Wait()
log.WithContextFields(ctx, log.Fields{"reason": reason}).Info("server: handleConn: done")
}
func (c *connection) initServerConn(ctx context.Context, srvCfg *ssh.ServerConfig) (*ssh.ServerConn, <-chan ssh.NewChannel, error) {
if c.cfg.Server.LoginGraceTime > 0 {
c.nconn.SetDeadline(time.Now().Add(time.Duration(c.cfg.Server.LoginGraceTime)))
defer c.nconn.SetDeadline(time.Time{})
}
sconn, chans, reqs, err := ssh.NewServerConn(c.nconn, srvCfg)
if err != nil {
msg := "connection: initServerConn: failed to initialize SSH connection"
logger := log.WithContextFields(ctx, log.Fields{"remote_addr": c.remoteAddr}).WithError(err)
if strings.Contains(err.Error(), "no common algorithm for host key") || err.Error() == "EOF" {
logger.Debug(msg)
} else {
logger.Warn(msg)
}
return nil, nil, err
}
go ssh.DiscardRequests(reqs)
return sconn, chans, err
}
func (c *connection) handleRequests(ctx context.Context, sconn *ssh.ServerConn, chans <-chan ssh.NewChannel, handler channelHandler) {
ctxlog := log.WithContextFields(ctx, log.Fields{"remote_addr": c.remoteAddr})
for newChannel := range chans {
ctxlog.WithField("channel_type", newChannel.ChannelType()).Info("connection: handle: new channel requested")
if newChannel.ChannelType() != "session" {
ctxlog.Info("connection: handleRequests: unknown channel type")
newChannel.Reject(ssh.UnknownChannelType, "unknown channel type")
continue
}
if !c.concurrentSessions.TryAcquire(1) {
ctxlog.Info("connection: handleRequests: too many concurrent sessions")
newChannel.Reject(ssh.ResourceShortage, "too many concurrent sessions")
metrics.SshdHitMaxSessions.Inc()
continue
}
channel, requests, err := newChannel.Accept()
if err != nil {
ctxlog.WithError(err).Error("connection: handleRequests: accepting channel failed")
c.concurrentSessions.Release(1)
continue
}
go func() {
defer func(started time.Time) {
duration := time.Since(started).Seconds()
metrics.SshdSessionDuration.Observe(duration)
ctxlog.WithFields(log.Fields{"duration_s": duration}).Info("connection: handleRequests: done")
}(time.Now())
defer c.concurrentSessions.Release(1)
// Prevent a panic in a single session from taking out the whole server
defer func() {
if err := recover(); err != nil {
ctxlog.WithField("recovered_error", err).Error("panic handling session")
}
}()
metrics.SliSshdSessionsTotal.Inc()
err := handler(ctx, sconn, channel, requests)
if err != nil {
c.trackError(ctxlog, err)
}
}()
}
// When a connection has been prematurely closed we block execution until all concurrent sessions are released
// in order to allow Gitaly complete the operations and close all the channels gracefully.
// If it didn't happen within timeout, we unblock the execution
// Related issue: https://gitlab.com/gitlab-org/gitlab-shell/-/issues/563
ctx, cancel := context.WithTimeout(ctx, EOFTimeout)
defer cancel()
c.concurrentSessions.Acquire(ctx, c.maxSessions)
}
func (c *connection) sendKeepAliveMsg(ctx context.Context, sconn *ssh.ServerConn, ticker *time.Ticker) {
ctxlog := log.WithContextFields(ctx, log.Fields{"remote_addr": c.remoteAddr})
for {
select {
case <-ctx.Done():
return
case <-ticker.C:
ctxlog.Debug("connection: sendKeepAliveMsg: send keepalive message to a client")
sconn.SendRequest(KeepAliveMsg, true, nil)
}
}
}
func (c *connection) trackError(ctxlog *logrus.Entry, err error) {
var apiError *client.ApiError
if errors.As(err, &apiError) {
return
}
if errors.Is(err, disallowedcommand.Error) {
return
}
grpcCode := grpcstatus.Code(err)
if grpcCode == grpccodes.Canceled || grpcCode == grpccodes.Unavailable {
return
} else if grpcCode == grpccodes.Internal && strings.Contains(err.Error(), NotOurRefError) {
return
}
metrics.SliSshdSessionsErrorsTotal.Inc()
ctxlog.WithError(err).Warn("connection: session error")
}
|
