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Fix misuse of PublicKeyCallback (#32810)

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Only upgrading the ssh package is not enough.
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wxiaoguang 2024-12-13 11:57:37 +08:00 committed by GitHub
parent 30008fcfcf
commit 2910f384d5
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3 changed files with 64 additions and 10 deletions
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2
go.mod
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@ -48,7 +48,7 @@ require (
github.com/ethantkoenig/rupture v1.0.1
github.com/felixge/fgprof v0.9.5
github.com/fsnotify/fsnotify v1.7.0
github.com/gliderlabs/ssh v0.3.7
github.com/gliderlabs/ssh v0.3.8
github.com/go-ap/activitypub v0.0.0-20240910141749-b4b8c8aa484c
github.com/go-ap/jsonld v0.0.0-20221030091449-f2a191312c73
github.com/go-chi/chi/v5 v5.1.0

4
go.sum
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@ -293,8 +293,8 @@ github.com/fxamacker/cbor/v2 v2.7.0 h1:iM5WgngdRBanHcxugY4JySA0nk1wZorNOpTgCMedv
github.com/fxamacker/cbor/v2 v2.7.0/go.mod h1:pxXPTn3joSm21Gbwsv0w9OSA2y1HFR9qXEeXQVeNoDQ=
github.com/git-lfs/pktline v0.0.0-20230103162542-ca444d533ef1 h1:mtDjlmloH7ytdblogrMz1/8Hqua1y8B4ID+bh3rvod0=
github.com/git-lfs/pktline v0.0.0-20230103162542-ca444d533ef1/go.mod h1:fenKRzpXDjNpsIBhuhUzvjCKlDjKam0boRAenTE0Q6A=
github.com/gliderlabs/ssh v0.3.7 h1:iV3Bqi942d9huXnzEF2Mt+CY9gLu8DNM4Obd+8bODRE=
github.com/gliderlabs/ssh v0.3.7/go.mod h1:zpHEXBstFnQYtGnB8k8kQLol82umzn/2/snG7alWVD8=
github.com/gliderlabs/ssh v0.3.8 h1:a4YXD1V7xMF9g5nTkdfnja3Sxy1PVDCj1Zg4Wb8vY6c=
github.com/gliderlabs/ssh v0.3.8/go.mod h1:xYoytBv1sV0aL3CavoDuJIQNURXkkfPA/wxQ1pL1fAU=
github.com/glycerine/go-unsnap-stream v0.0.0-20181221182339-f9677308dec2/go.mod h1:/20jfyN9Y5QPEAprSgKAUr+glWDY39ZiUEAYOEv5dsE=
github.com/glycerine/goconvey v0.0.0-20190410193231-58a59202ab31/go.mod h1:Ogl1Tioa0aV7gstGFO7KhffUsb9M4ydbEbbxpcEDc24=
github.com/go-ap/activitypub v0.0.0-20240910141749-b4b8c8aa484c h1:82lzmsy5Nr6JA6HcLRVxGfbdSoWfW45C6jnY3zFS7Ks=

68
modules/ssh/ssh.go
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@ -13,10 +13,12 @@ import (
"errors"
"fmt"
"io"
"maps"
"net"
"os"
"os/exec"
"path/filepath"
"reflect"
"strconv"
"strings"
"sync"
@ -33,9 +35,22 @@ import (
gossh "golang.org/x/crypto/ssh"
)
type contextKey string
// The ssh auth overall works like this:
// NewServerConn:
// serverHandshake+serverAuthenticate:
// PublicKeyCallback:
// PublicKeyHandler (our code):
// reset(ctx.Permissions) and set ctx.Permissions.giteaKeyID = keyID
// pubKey.Verify
// return ctx.Permissions // only reaches here, the pub key is really authenticated
// set conn.Permissions from serverAuthenticate
// sessionHandler(conn)
//
// Then sessionHandler should only use the "verified keyID" from the original ssh conn, but not the ctx one.
// Otherwise, if a user provides 2 keys A (a correct one) and B (public key matches but no private key),
// then only A succeeds to authenticate, sessionHandler will see B's keyID
const giteaKeyID = contextKey("gitea-key-id")
const giteaPermissionExtensionKeyID = "gitea-perm-ext-key-id"
func getExitStatusFromError(err error) int {
if err == nil {
@ -61,8 +76,32 @@ func getExitStatusFromError(err error) int {
return waitStatus.ExitStatus()
}
// sessionPartial is the private struct from "gliderlabs/ssh/session.go"
// We need to read the original "conn" field from "ssh.Session interface" which contains the "*session pointer"
// https://github.com/gliderlabs/ssh/blob/d137aad99cd6f2d9495bfd98c755bec4e5dffb8c/session.go#L109-L113
// If upstream fixes the problem and/or changes the struct, we need to follow.
// If the struct mismatches, the builtin ssh server will fail during integration tests.
type sessionPartial struct {
sync.Mutex
gossh.Channel
conn *gossh.ServerConn
}
func ptr[T any](intf any) *T {
// https://pkg.go.dev/unsafe#Pointer
// (1) Conversion of a *T1 to Pointer to *T2.
// Provided that T2 is no larger than T1 and that the two share an equivalent memory layout,
// this conversion allows reinterpreting data of one type as data of another type.
v := reflect.ValueOf(intf)
p := v.UnsafePointer()
return (*T)(p)
}
func sessionHandler(session ssh.Session) {
keyID := fmt.Sprintf("%d", session.Context().Value(giteaKeyID).(int64))
// here can't use session.Permissions() because it only uses the value from ctx, which might not be the authenticated one.
// so we must use the original ssh conn, which always contains the correct (verified) keyID.
sshConn := ptr[sessionPartial](session)
keyID := sshConn.conn.Permissions.Extensions[giteaPermissionExtensionKeyID]
command := session.RawCommand()
@ -164,6 +203,23 @@ func sessionHandler(session ssh.Session) {
}
func publicKeyHandler(ctx ssh.Context, key ssh.PublicKey) bool {
// The publicKeyHandler (PublicKeyCallback) only helps to provide the candidate keys to authenticate,
// It does NOT really verify here, so we could only record the related information here.
// After authentication (Verify), the "Permissions" will be assigned to the ssh conn,
// then we can use it in the "session handler"
// first, reset the ctx permissions (just like https://github.com/gliderlabs/ssh/pull/243 does)
// it shouldn't be reused across different ssh conn (sessions), each pub key should have its own "Permissions"
oldCtxPerm := ctx.Permissions().Permissions
ctx.Permissions().Permissions = &gossh.Permissions{}
ctx.Permissions().Permissions.CriticalOptions = maps.Clone(oldCtxPerm.CriticalOptions)
setPermExt := func(keyID int64) {
ctx.Permissions().Permissions.Extensions = map[string]string{
giteaPermissionExtensionKeyID: fmt.Sprint(keyID),
}
}
if log.IsDebug() { // <- FingerprintSHA256 is kinda expensive so only calculate it if necessary
log.Debug("Handle Public Key: Fingerprint: %s from %s", gossh.FingerprintSHA256(key), ctx.RemoteAddr())
}
@ -238,8 +294,7 @@ func publicKeyHandler(ctx ssh.Context, key ssh.PublicKey) bool {
if log.IsDebug() { // <- FingerprintSHA256 is kinda expensive so only calculate it if necessary
log.Debug("Successfully authenticated: %s Certificate Fingerprint: %s Principal: %s", ctx.RemoteAddr(), gossh.FingerprintSHA256(key), principal)
}
ctx.SetValue(giteaKeyID, pkey.ID)
setPermExt(pkey.ID)
return true
}
@ -266,8 +321,7 @@ func publicKeyHandler(ctx ssh.Context, key ssh.PublicKey) bool {
if log.IsDebug() { // <- FingerprintSHA256 is kinda expensive so only calculate it if necessary
log.Debug("Successfully authenticated: %s Public Key Fingerprint: %s", ctx.RemoteAddr(), gossh.FingerprintSHA256(key))
}
ctx.SetValue(giteaKeyID, pkey.ID)
setPermExt(pkey.ID)
return true
}