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crypto/tls: conflicting lock order in Handshake() and Read() #38870

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BurtonQin opened this issue May 5, 2020 · 2 comments
Open

crypto/tls: conflicting lock order in Handshake() and Read() #38870

BurtonQin opened this issue May 5, 2020 · 2 comments
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NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@BurtonQin
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BurtonQin commented May 5, 2020

What version of Go are you using (go version)?

1.14.2

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/boqin/.cache/go-build"
GOENV="/home/boqin/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/boqin/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/data/suz305/go-workspace/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/data/suz305/go-workspace/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build519488021=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I analyzed the source code crypto/tls/conn.go and found a possible conflicting lock order which may lead to deadlock.
If Conn.Handshake() and Conn.Read() are executed concurrently in two threads, then a deadlock may occur.
In crypto/tls/conn.go

type Conn struct {
	...
	handshakeMutex sync.Mutex
	...

	// input/output
	in, out   halfConn
	
}
type halfConn struct {
	sync.Mutex

	...
}
  1. Conn.handshakeMutex.Lock() -> Conn.in.Lock()
    In Handshake(): Conn.handshakeMutex.Lock() is on L1344. Conn.in.Lock() is on L1354

    go/src/crypto/tls/conn.go

    Lines 1343 to 1355 in 9b18968

    func (c *Conn) Handshake() error {
    c.handshakeMutex.Lock()
    defer c.handshakeMutex.Unlock()
    if err := c.handshakeErr; err != nil {
    return err
    }
    if c.handshakeComplete() {
    return nil
    }
    c.in.Lock()
    defer c.in.Unlock()

  2. Conn.in.Lock() -> Conn.handshakeMutex.Lock()
    In Read(): c.in.Lock() is on L1243. handlePostHandshakeMessage() is on L1251.

    go/src/crypto/tls/conn.go

    Lines 1233 to 1251 in 9b18968

    func (c *Conn) Read(b []byte) (int, error) {
    if err := c.Handshake(); err != nil {
    return 0, err
    }
    if len(b) == 0 {
    // Put this after Handshake, in case people were calling
    // Read(nil) for the side effect of the Handshake.
    return 0, nil
    }
    c.in.Lock()
    defer c.in.Unlock()
    for c.input.Len() == 0 {
    if err := c.readRecord(); err != nil {
    return 0, err
    }
    for c.hand.Len() > 0 {
    if err := c.handlePostHandshakeMessage(); err != nil {

    Then handleRenegotiation() is on L1178.

    go/src/crypto/tls/conn.go

    Lines 1176 to 1179 in 9b18968

    func (c *Conn) handlePostHandshakeMessage() error {
    if c.vers != VersionTLS13 {
    return c.handleRenegotiation()
    }

    Conn.handshakeMutex.Lock() is on L1164

    go/src/crypto/tls/conn.go

    Lines 1164 to 1172 in 9b18968

    c.handshakeMutex.Lock()
    defer c.handshakeMutex.Unlock()
    atomic.StoreUint32(&c.handshakeStatus, 0)
    if c.handshakeErr = c.clientHandshake(); c.handshakeErr == nil {
    c.handshakes++
    }
    return c.handshakeErr
    }

What did you expect to see?

--

What did you see instead?

--

@networkimprov
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networkimprov commented May 7, 2020

cc @FiloSottile

@dmitshur
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dmitshur commented May 9, 2020

Also /cc @katiehockman.

@dmitshur dmitshur added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label May 9, 2020
@dmitshur dmitshur added this to the Backlog milestone May 9, 2020
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