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|
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/client"
"gitlab.com/gitlab-org/gitlab-shell/internal/config"
"gitlab.com/gitlab-org/gitlab-shell/internal/metrics"
"gitlab.com/gitlab-org/labkit/log"
)
const KeepAliveMsg = "keepalive@openssh.com"
var EOFTimeout = 10 * time.Second
type connection struct {
cfg *config.Config
concurrentSessions *semaphore.Weighted
nconn net.Conn
maxSessions int64
remoteAddr string
}
type channelHandler func(*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) {
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).Warn("panic handling session")
}
}()
metrics.SliSshdSessionsTotal.Inc()
err := handler(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
}
grpcCode := grpcstatus.Code(err)
if grpcCode == grpccodes.Canceled || grpcCode == grpccodes.Unavailable {
return
}
metrics.SliSshdSessionsErrorsTotal.Inc()
ctxlog.WithError(err).Warn("connection: session error")
}
|
