syscall: ExtraFiles FD used to set controlling TTY instead of SysProcAttr.Ctty field #29458

sipsma · 2018-12-29T21:11:30Z

What did you do?

In some corner cases, cmd/exec will start a child process with a controlling tty FD from the ExtraFiles field of Cmd instead of the FD specified in SysProcAttr.Ctty.

This occurs when the FD number of SysProcAttr.Ctty in the parent is 0, 1, 2 or 3+i, where i is an index that has been populated in the ExtraFiles field of the Cmd struct.

This happens because the dup2 loop of forkAndExecInChild1 runs before the ioctl calls to set the Ctty. When making the ioctl calls, it's still is using the Ctty FD value passed in from the parent, so if the child process happens to dup2 over that FD value, the Ctty passed from the parent is closed and the child's ExtraFile FD is used instead of the Ctty FD configured by the parent. This usually results in a ENOTTY error (unless the ExtraFile happens to also be a TTY).

The following reproducing code (compiled with CGo enabled, on Linux w/ glibc) first creates a child process where the bug doesn't occur and then one where the bug does occur. When the bug occurs, forkAndExecInChild1 will incorrectly use the parent's FD 10 (/dev/null) when making the ioctl to setup the ctty even though SysProcAttr configured it to use the parent's FD 11.

package main

import (
        /*
                #include <pty.h>
                #cgo LDFLAGS: -lutil
        */
        "C"

        "fmt"
        "os"
        "os/exec"
        "syscall"
)

func main() {
    // Case with expected behavior.
    // The parent process opens files with descriptors set to:
    // * 5 -> /dev/null
    // * 7 -> PTY (from under /dev/pts/)
    // The child process is configured with the following valid mappings from the parent
    // * 6 in the child -> 5 in the parent (/dev/null)
    // * Ctty in the child -> 7 in the parent (PTY)
    runChildWithCtty(5, 6, 7)

    // Case where the bug occurs (child process fails to start with ENOTTY).
    // The parent process opens files with descriptors set to:
    // * 10 -> /dev/null
    // * 11 -> PTY (from under /dev/pts/)
    // The child process is configured with the following valid mappings from the parent
    // * 11 in the child -> 10 in the parent (/dev/null)
    // * Ctty in the child -> 11 in the parent (PTY)
    runChildWithCtty(10, 11, 11)
}

// Run a child process (arbitrarily /bin/true) with
// * An ExtraFile where the FD is parentExtraFileFdNum in the parent and will be set to childExtraFileFdNum in the child
// * A Ctty where the PTY has FD num set to parentPtyFdNum
func runChildWithCtty(parentExtraFileFdNum int, childExtraFileFdNum int, parentPtyFdNum int) {
        childCmd := exec.Command("/bin/true")
        childCmd.ExtraFiles = make([]*os.File, childExtraFileFdNum-2)

        childCmd.ExtraFiles[childExtraFileFdNum-3] = openNormalFileAtFd(parentExtraFileFdNum)
        childCmd.SysProcAttr = &syscall.SysProcAttr{
                Setsid: true,
                Setctty: true,
                Ctty: openPtyAtFd(parentPtyFdNum),
        }

        err := childCmd.Run()
        if err != nil {
                panic(fmt.Sprintf("failed to run child process with ParentExtraFileFdNum=%d, ChildExtraFileFd=%d, ParentPtyFd=%d: %v", parentExtraFileFdNum, childExtraFileFdNum, parentPtyFdNum, err))
        } else {
                fmt.Printf("successfully ran child process with ParentExtraFileFdNum=%d, ChildExtraFileFd=%d, ParentPtyFd=%d\n\n", parentExtraFileFdNum, childExtraFileFdNum, parentPtyFdNum)
        }
}

// open a pty up and dup2 it to the requested FD num
func openPtyAtFd(wantedFd int) int {
        m := C.int(0)
        s := C.int(0)

        _, err := C.openpty(&m, &s, nil, nil, nil)
        if err != nil {
                panic(fmt.Sprintf("failed to open pty: %v", err))
        }

        goS := int(s)

        if goS != wantedFd {
                err = syscall.Dup2(goS, wantedFd)
                if err != nil {
                        panic(fmt.Sprintf("failed to dup2: %v", err))
                }
                syscall.Close(goS)
        }

        return wantedFd
}

// open /dev/null and dup2 it to the requested FD num
func openNormalFileAtFd(wantedFd int) *os.File {
        f, err := os.Open(os.DevNull)
        if err != nil {
                panic(fmt.Sprintf("failed to open devnull: %v", err))
        }

        actualFd := int(f.Fd())

        if actualFd != wantedFd {
                err = syscall.Dup2(actualFd, wantedFd)
                if err != nil {
                        panic(fmt.Sprintf("failed to dup2: %v", err))
                }
                f.Close()
                return os.NewFile(uintptr(wantedFd), f.Name())
        } else {
                return f
        }
}

This might be in something of a grey area as to whether it's a bug or expected behavior, but I'd consider this a bug because:

When I configure the SysProcAttr.Ctty field, I am providing an FD of the parent, so it's very surprising that in some corner cases it ends up instead being a reference to an FD in the child process
To workaround this behavior, our codebase in which this was originally encountered now has to jump through a bunch of hoops to check that an FD number of the parent (the pty) never accidentally has the same value of completely unrelated FDs (set in ExtraFiles) that will be set in the child. It seems like the whole point of the interface given by cmd/exec is to make the FD numbers of the parent and child independent of one another and only related by a mapping, saving users from having to think about corner cases of FD inheritance.
- We don't have direct control over the initial FD values returns by various syscalls, so we end up having to either dup FDs in a loop until they no longer conflict between the Ctty field and ExtraFiles or make the FD numbers of our child process ExtraFiles dynamically configurable. Neither is ideal.

What did you expect to see?

I expected both cases in the reproducing code to work, making the ioctl call to set the ctty using the SysProcAttr field as configured in the parent process.

Running strace -f -b execve -e 'trace=desc' ./main, this is the (filtered) output in the working case:

[pid 15680] openat(AT_FDCWD, "/dev/null", O_RDONLY|O_CLOEXEC) = 3
[pid 15680] dup2(3, 5)                  = 5
[pid 15680] close(3)                    = 0
[pid 15680] open("/dev/ptmx", O_RDWR)   = 3
[pid 15680] close(7)                    = 0
[pid 15680] close(6)                    = 0
[pid 15680] close(6)                    = 0
[pid 15680] open("/dev/pts/13", O_RDWR|O_NOCTTY) = 6
[pid 15680] dup2(6, 7)                  = 7
[pid 15680] close(6)                    = 0
[pid 15680] openat(AT_FDCWD, "/dev/null", O_RDONLY|O_CLOEXEC) = 6
[pid 15680] openat(AT_FDCWD, "/dev/null", O_WRONLY|O_CLOEXEC) = 8
[pid 15680] openat(AT_FDCWD, "/dev/null", O_WRONLY|O_CLOEXEC) = 9
[pid 15680] pipe2([10, 11], O_CLOEXEC)  = 0
Process 15687 attached
[pid 15687] dup2(5, 10)                 = 10
[pid 15687] dup2(6, 0)                  = 0
[pid 15687] dup2(8, 1)                  = 1
[pid 15687] dup2(9, 2)                  = 2
[pid 15687] close(3)                    = 0
[pid 15687] close(4)                    = 0
[pid 15687] close(5)                    = 0
[pid 15687] dup2(10, 6)                 = 6
[pid 15687] ioctl(7, TIOCSCTTY, 1)      = 0

What did you see instead?

In the case where the bug occurs, this is the filtered strace output:

[pid 15680] openat(AT_FDCWD, "/dev/null", O_RDONLY|O_CLOEXEC) = 6
[pid 15680] dup2(6, 10)                 = 10
[pid 15680] close(6)                    = 0
[pid 15680] open("/dev/ptmx", O_RDWR)   = 6
[pid 15680] open("/dev/pts/14", O_RDWR|O_NOCTTY) = 8
[pid 15680] dup2(8, 11)                 = 11
[pid 15680] close(8)                    = 0
[pid 15680] openat(AT_FDCWD, "/dev/null", O_RDONLY|O_CLOEXEC <unfinished ...>
[pid 15680] <... openat resumed> )      = 8
[pid 15680] openat(AT_FDCWD, "/dev/null", O_WRONLY|O_CLOEXEC) = 9
[pid 15680] openat(AT_FDCWD, "/dev/null", O_WRONLY|O_CLOEXEC) = 12
[pid 15680] pipe2([13, 14], O_CLOEXEC)  = 0
Process 15688 attached
[pid 15688] dup2(10, 13)                = 13
[pid 15688] dup2(8, 0)                  = 0
[pid 15688] dup2(9, 1)                  = 1
[pid 15688] dup2(12, 2)                 = 2
[pid 15688] close(3)                    = 0
[pid 15688] close(4)                    = 0
[pid 15688] close(5)                    = 0
[pid 15688] close(6)                    = 0
[pid 15688] close(7)                    = 0
[pid 15688] close(8)                    = 0
[pid 15688] close(9)                    = 0
[pid 15688] close(10)                   = 0
[pid 15688] dup2(13, 11)                = 11
[pid 15688] ioctl(11, TIOCSCTTY, 1)     = -1 ENOTTY (Inappropriate ioctl for device)

Even though the child process does call the ioctl on FD 11 at the end, 11 was previously overwritten by a dup2 call (from 13, which itself was dup2'd from 10, which is a FD configured in ExtraFiles, not Ctty).

So the end effect is that the parent's FD 10 from ExtraFiles was used as the Ctty instead of the parent's FD 11.

Does this issue reproduce with the latest release (go1.11.4)?

Yes

System details

go version go1.11.4 linux/amd64
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/sipsma/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/sipsma/go"
GOPROXY=""
GORACE=""
GOROOT="/local/home/sipsma/go"
GOTMPDIR=""
GOTOOLDIR="/local/home/sipsma/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
GOROOT/bin/go version: go version go1.11.4 linux/amd64
GOROOT/bin/go tool compile -V: compile version go1.11.4
uname -sr: Linux 4.9.124-0.1.ac.198.73.329.metal1.x86_64
/lib64/libc.so.6: GNU C Library stable release version 2.12, by Roland McGrath et al.
gdb --version: GNU gdb (GDB) Amazon Linux (7.2-50.11.amzn1)

The text was updated successfully, but these errors were encountered:

gopherbot · 2019-05-25T20:51:03Z

Change https://golang.org/cl/178919 mentions this issue: syscall: use Ctty before fd shuffle

ianlancetaylor · 2019-06-21T16:57:57Z

I'm starting to wonder whether this is actually a bug. The change in behavior has broken a couple of existing programs.

Perhaps we should instead clearly define the Ctty field as being the file descriptor number in the child, not the parent. Then the code before CL 178919 would work fine, provided we can always assume that the ctty should be a descriptor that is open in the child. If you wrote your code with that understanding, would that clarify matters?

ianlancetaylor · 2019-06-21T16:58:16Z

Marking as release-blocker to decide whether to keep or revert the change.

sipsma · 2019-06-21T17:46:36Z

@ianlancetaylor I see where you're coming from but still have some concerns.

IIRC The behavior before CL 178919 was that sometimes the parent FD was used and sometimes the child FD was used. So even if you go with the model of Ctty specifying the child FD, I think there would still need to be a different fix to ensure that it's only the child FD that is ever used.

Given the above, I wonder if changing this behavior with that different fix would end up just breaking a different set of existing programs. It seems entirely possible to me that programs out there are using this interface but their parent process and child process always have FDs open in the right pattern such that their child ends up using a parent FD as a Ctty.

ianlancetaylor · 2019-06-21T17:54:05Z

It seems to me that before CL 178919 we always used the child FD. In what circumstances would you say that we used the parent FD?

sipsma · 2019-06-21T18:02:37Z

In my original post, the first test case, runChildWithCtty(5, 6, 7), results in the parent FD 7 being used as the Ctty of the child. FD 7 isn't set in the child process.

The second test case, runChildWithCtty(10, 11, 11) has the behavior you're describing where the child FD is used. I think it's the inconsistency in behavior that's the real bug.

ianlancetaylor · 2019-06-21T18:08:57Z

OK, I'm not sure what happens when the controlling terminal is closed. Is it meaningful to set the ctty of a process and then close that descriptor?

sipsma · 2019-06-21T18:22:49Z

Yeah I believe there's no requirement at least on Linux (not sure about Posix in general) that the child actually keep the FD open.

The original context in which I encountered this bug was a parent process on Linux that managed a bunch of children, each one of which was in its own session with its own Ctty. The parent process kept the Ctty FD open after the child spawned until it wanted the child process's session to end, at which time the parent closed the Ctty (which results in SIGHUP being sent to every process in the child's session). This worked consistently in the "use parent FD as Ctty" case. It was a very rare occurrence that the code would randomly hit the "use child FD as Ctty" case and then things would break.

I can see that others were probably in the reverse situation and relied on the "use child FD as Ctty" case, but it seems like this may be a choice between who you want to break. I'm obviously a bit biased, but the "use parent FD as Ctty" behavior seems more straightforward. You don't need to coordinate between the Ctty and ExtraFiles fields in the parent and the child doesn't need to have an extra FD sitting around it may not have any use for.

ianlancetaylor · 2019-06-21T18:50:59Z

Thanks, that seems persuasive.

neild · 2019-06-25T19:39:59Z

This change has broken https://github.com/google/goexpect/, and I'm not certain that package was doing anything wrong.

The goexpect package sets up a SysProcAddr here:

	cmd := exec.Command(command[0], command[1:]...)
	// This ties the commands Stdin,Stdout & Stderr to the virtual terminal we created
	cmd.Stdin, cmd.Stdout, cmd.Stderr = pty.Slave, pty.Slave, pty.Slave
	// New process needs to be the process leader and control of a tty
	cmd.SysProcAttr = &syscall.SysProcAttr{
		Setsid:  true,
		Setctty: true}

SysProcAttr.Ctty is 0. Prior to this change, that sets the controlling terminal to cmd.Stdin (since Ctty refers to the FD in the child). After this change, it sets the controlling terminal to os.Stdin (Ctty refers to the FD in the parent).

Perhaps it would have been best if SysProcAttr.Ctty had always referred to a FD in the parent, but unless I'm missing something changing it breaks working code that wasn't doing anything wrong.

@sipsma

IIRC The behavior before CL 178919 was that sometimes the parent FD was used and sometimes the child FD was used.

I don't think this is correct; from my read the controlling TTY was always set in the child immediately before calling exec.

sipsma · 2019-06-25T20:06:29Z

@neild I don't think there's any debate that the Ctty was always consistently set in the child. The issue was whether the FD being used to set the Ctty was a reference to an FD opened in the parent or a reference to an FD opened in the child.

The behavior before the fix was inconsistent; if you specified Ctty: 4 (for example), sometimes you would end up referring to what the parent has open at FD 4, sometimes you would end up referring to what the child has opened as FD 4.

Given this inconsistency needs to be fixed and will end up breaking behavior no matter what, my preference is the behavior that results in the clearest+simplest interface and the one with the least extraneous requirements, but that decision is up to the Go maintainers obviously. I'll just also mention that the code you posted would be updated to

cmd.SysProcAttr = &syscall.SysProcAttr{
		Setsid:  true,
		Setctty: true,
                Ctty: pty.Slave}

so while I agree the fix breaks your existing code, the updates required are at least pretty minimal and result in being more explicit (if that's any consolation).

sipsma · 2019-06-25T20:12:12Z

This does bring up the point that it would probably be highly beneficial for the docs to make the behavior very explicit. Right now they are pretty ambiguous as to whether the Ctty FD is a reference to the parent or child, which is part of the source of confusion here: https://golang.org/pkg/syscall/#SysProcAttr

neild · 2019-06-25T20:14:41Z

The behavior before the fix was inconsistent; if you specified Ctty: 4 (for example), sometimes you would end up referring to what the parent has open at FD 4, sometimes you would end up referring to what the child has opened as FD 4.

If you specified Ctty: 4, how would you get anything other than the child's FD 4? The controlling terminal is set in the child immediately before calling exec. It is a reference to a FD in the child.

Perhaps your point is that you don't have control over what FD 4 in the child is. But you do have control over FDs 0, 1, and 2, which is precisely the case which is broken here.

sipsma · 2019-06-25T20:28:15Z

Perhaps your point is that you don't have control over what FD 4 in the child is.

Yes, in fact if you are a user just going by the docs, FD 4 is not even supposed to be open in the child (once the final child process is exec'd it will be closed via CLOEXEC). That's why it seemed entirely reasonable to assume that the FD must refer the FD as set in the parent. It wouldn't make sense to rely on a 100% internal implementation detail such as the fact that an FD from the parent still happens to be opened in the child process at a given time.

Again, I agree your code is broken by this change as is, but switching the behavior the other way (make Ctty always refer to child FDs`) is still a breaking change, just for a different set of cases.

neild · 2019-06-25T20:38:24Z

Also, your suggested fix is not universally accurate (although it would work here).

Consider existing code:

cmd.Stdin, cmd.Stdout, cmd.Stderr = f0, f1, f2
cmd.SysProcAttr = &syscall.SysProcAttr{
  Setsid:  true,
  Setctty: true,
  Ctty: 0,
}

In Go 1.12 and earlier, this will always and consistently set the child's ctty to f0. (First f0 is shuffled to FD 0, second we set the ctty.)

After the change to redefine Ctty, this needs to be written as:

cmd.Stdin, cmd.Stdout, cmd.Stderr = f0, f1, f2
cmd.SysProcAttr = &syscall.SysProcAttr{
  Setsid:  true,
  Setctty: true,
  Ctty: f0.Fd(),
}

This will also work in Go 1.12 and earlier, unless f0's FD in the parent is 1 or 2. In Go 1.12 we will:

Shuffle f0 to FD 0, setting the original FD of f0 to close-on-exec.
Shuffle f1 and f2 to FDs 1 and 2. If f0's original FD is 1 or 2, it will be clobbered.
Set the ctty to whatever f0's original FD is.

This is perhaps an obscure case, but it indicates that there is no general way to write code which is safe with both the old and new APIs. (Also, it's the exact corner case which motivates this change.)

Again, I agree your code is broken by this change as is, but switching the behavior the other way (make Ctty always refer to child FDs`) is still a breaking change, just for a different set of cases

Prior to this change, it is possible to write code which safely sets the controlling terminal in the child.

After this change, it is very difficult to write such code which is correct with both older and newer Go versions.

sipsma · 2019-06-25T21:08:25Z

After this change, it is very difficult to write such code which is correct with both older and newer Go versions.

Agree, you would need an implementation for go1.12 and older and a separate one for go1.13, which can be done with build tags AFAIK but is nonetheless unfortunate as it's code that's going to need to sit around until you are willing to tell your users that go 1.13+ is a strict requirement.

However, for the other set of users who would be broken by a switch to always using the child FD, they now would need to permanently have code that sets the Ctty FD in ExtraFiles and update their child process to close the file they don't actually need (or accept that another file is going to be opened in the child and possibly be passed down to descendants).

Either way, some set of users of the library are going to end having to include more extraneous code in their codebase because of the previous inconsistent behavior. It's just going to come down to which the maintainers want to impose I suppose.

neild · 2019-06-25T21:19:35Z

for users broken by the switch to always using the child FD,

This is not a switch. This is the previous behavior. SysProcAttr.Ctty has always referred to a file descriptor in the child. CL/178919 redefines it, breaking previously correct programs. This change should be reverted.

sipsma · 2019-06-25T21:31:47Z

SysProcAttr.Ctty has always referred to a file descriptor in the child.

But it was inconsistent whether it referred to a file that was actually specified by the user to be opened in the child or it was another FD that temporarily existed due to an internal implementation detail, which is what needed to be fixed.

I've made my views clear and can't personally make a judgement call on which users the maintainers should break. I would just would say that if CL/178919 is reverted, then there still needs to be another fix to make Ctty consistently refer to a FD that is specified in ExtraFiles (which like I said before will just end up breaking another set of existing users and impose extra requirements on them).

ianlancetaylor · 2019-06-26T00:42:18Z

I hadn't considered the necessity of calling the Fd method, which has side effects. I think it may be better to revert CL 178919, document Ctty as being the child's descriptor number, and accept that there is no way to start a child with a closed ctty descriptor. Perhaps for 1.14 we can return an error if Ctty is set to a descriptor number that does not match Files.

sipsma · 2019-06-26T01:13:57Z

@ianlancetaylor I can understand (though respectfully disagree with) reverting CL 178919 and replacing it with a change that returns an error in the case where ExtraFiles doesn't have the Ctty being specified.

However, only reverting it and not fixing the inconsistent behavior (one way or another) concerns me as a user of the library. For me, this appeared as a rare bug that just caused an error, but there are other scenarios in which this inconsistent behavior is worse.

Say a user of the library meant to set a pty file as FD 3 via ExtraFiles and set Ctty: 3, but they made a mistake and forgot to append it or accidentally provided nil to ExtraFiles. Without any fix, the child will now subtly end up using the parent's FD 3. If that FD is a tty for something else, what should have just been an error instead succeeds and results in a child process running with a random other controlling TTY that just happened to also be open at the time in the parent. The implications here run the gambit from just creating an extremely hard to diagnose bug to potential security concerns. This really seems like something that should be addressed in the code, not just docs, if at all possible before 1.14.

ianlancetaylor · 2019-06-26T01:24:03Z

I think this change has proven to be fragile, breaking various existing packages, and I think it's too late in the 1.13 release cycle to mess with it. That is why I suggest fixing it in 1.14. While I agree that the current behavior has its problems, at least 1.13 won't be any worse than any previous release.

ddevault · 2020-05-05T13:51:44Z

It seems that this change breaks the following patch to github.com/creack/pty:

creack/pty#75

Which is necessary to support interactive programs which open /dev/tty for user-interaction and consume actionable data from stdin, such as less, fzf, vipe, and so on. This breaks the user interaction model of aerc.

ianlancetaylor · 2020-05-05T23:52:59Z

@ddevault If tty is going to be open in the child process, then it must have a file descriptor in the child process. When using os/exec.Cmd as the creack/pty code does, tty must be in Stdin or Stdout or Stderr or ExtraFiles. If it isn't in any of those, then it will be closed when the child process runs. If it is in one of those, that gives you the file descriptor number that you should use in Ctty.

Right now the creack code is setting Ctty to the parent's file descriptor number. That is working (assuming that it is working) by accident. The correct fix is to ensure that tty is passed to the child somewhere, and set Ctty to the appropriate descriptor number. If it is possible for all of Stdin, Stdout, Stderr to be set, the simplest approach would be to always add tty to ExtraFiles, and set Ctty to 3. That will work for old versions of Go and also for the upcoming 1.15 release.

ddevault · 2020-05-06T01:56:55Z

It looks like creack was able to put together this fix: creack/pty#97

ianlancetaylor · 2020-05-06T03:21:51Z

OK, looks like that version works because it leaves the Ctty field as zero, meaning that the tty is taking from standard input.

The Ctty field is a child descriptor number when Setctty is set, but a parent descriptor when Foreground is set. This is absurd but changing either behavior breaks existing programs. With this change we at least document how it works. For golang#29458 Change-Id: If9cf0a1a1e6ed0d4a4edae5043016d5b4ee3308b Reviewed-on: https://go-review.googlesource.com/c/go/+/229768 Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Damien Neil <dneil@google.com>

Ctty was always handled as a child descriptor, but in some cases passing a parent descriptor would also work. This depended on unpredictable details of the implementation. Reject those cases to avoid confusion. Also reject setting both Setctty and Foreground, as they use Ctty in incompatible ways. It's unlikely that any programs set both fields, as they don't make sense together. Fixes golang#29458 Change-Id: Ieba2d625711fd4b82c8e65e1feed02fd1fb25e6d Reviewed-on: https://go-review.googlesource.com/c/go/+/231638 Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Damien Neil <dneil@google.com>

The fix is needed to mitigate consequences of golang/go#29458 "golang breaking change" that causes following test failures on etcd end: --- FAIL: TestCtlV2Set (0.00s) ctl_v2_test.go:552: could not start etcd process cluster (fork/exec ../../bin/etcd: Setctty set but Ctty not valid in child) --- FAIL: TestCtlV2SetQuorum (0.00s) ctl_v2_test.go:552: could not start etcd process cluster (fork/exec ../../bin/etcd: Setctty set but Ctty not valid in child) --- FAIL: TestCtlV2SetClientTLS (0.00s) ctl_v2_test.go:552: could not start etcd process cluster (fork/exec ../../bin/etcd: Setctty set but Ctty not valid in child)

See golang/go#29458 and https://go-review.googlesource.com/c/go/+/231638. Go 1.15 added a check for a child spawning bug, where ctty was set to a wrong file descriptor. `Ctty` in `SysProcAttr` should be set to a file descriptor _in a child process_, but we were setting it to a file descriptor _in a parent process_. This was working by accident, but is now caught by `os/exec`. Instead, leave it as 0, which will default it to the file descriptor of stdin. In our case, stdin is already set to the tty.

`Ctty` in `SysProcAttr` should be set to a file descriptor _in a child process_, but we were setting it to a file descriptor _in a parent process_. This was working by accident, but is now caught by `os/exec`. Instead, leave it as 0, which will default it to the fd of stdin. In our case, stdin is already set to the tty. See: golang/go#29458

`Ctty` in `SysProcAttr` should be set to a fd in a child process, but we were setting it to a fd in the parent process. This was working by accident, but now a panic is raised by `os/exec`. See: golang/go#29458

Starting with golang 1.5, setting Ctty value result in `Setctty set but Ctty not valid in child` error, as part of golang/go#29458 . This commit lifts the fix in creack/pty#97 .

Upgrade to golang 1.15 Starting with golang 1.5, setting Ctty value result in `Setctty set but Ctty not valid in child` error, as part of golang/go#29458 . This commit lifts the fix in creack/pty#97 .

Fix tty issue in go 1.15.x golang/go#29458 creack/pty#96

ianlancetaylor changed the title ~~ExtraFiles FD used to set controlling TTY instead of SysProcAttr.Ctty field~~ syscall: ExtraFiles FD used to set controlling TTY instead of SysProcAttr.Ctty field Dec 30, 2018

ianlancetaylor added the NeedsFix The path to resolution is known, but the work has not been done. label Dec 30, 2018

ianlancetaylor added this to the Go1.13 milestone Dec 30, 2018

gopherbot closed this as completed in 103b5b6 May 30, 2019

ianlancetaylor reopened this Jun 21, 2019

ianlancetaylor added the release-blocker label Jun 21, 2019

ianlancetaylor closed this as completed Jun 21, 2019

neild mentioned this issue Jun 25, 2019

Go 1.13: Spawn fails with "operation not permitted" google/goexpect#40

Closed

neild reopened this Jun 25, 2019

gopherbot closed this as completed in be08e10 May 1, 2020

myitcv mentioned this issue May 5, 2020

Setctty set but Ctty not valid in child with Go +be08e10b3b creack/pty#96

Closed

creack mentioned this issue May 5, 2020

Add StartWithAttrs to allow bypassing setsid/setctty creack/pty#97

Merged

ptabor mentioned this issue Aug 4, 2020

tests/e2e: Update github.com/creack/pty v1.1.7 -> v1.1.11 etcd-io/etcd#12199

Merged

tri-adam mentioned this issue Aug 18, 2020

fix: address 'Ctty not valid in child' in e2e-test apptainer/singularity#5509

Merged

awly mentioned this issue Aug 18, 2020

Don't set ctty on the executed shell process gravitational/teleport#4227

Merged

gustavosbarreto mentioned this issue Aug 28, 2020

agent: Don't set ctty fd shellhub-io/shellhub#350

Merged

notnoop pushed a commit to hashicorp/nomad that referenced this issue Sep 8, 2020

Avoid setting ctty

2798be1

Starting with golang 1.5, setting Ctty value result in `Setctty set but Ctty not valid in child` error, as part of golang/go#29458 . This commit lifts the fix in creack/pty#97 .

notnoop mentioned this issue Sep 9, 2020

Upgrade to golang 1.15 hashicorp/nomad#8858

Merged

9cat mentioned this issue Nov 2, 2020

Error: Setctty set but Ctty not valid in child cespare/reflex#79

Closed

clrpackages pushed a commit to clearlinux-pkgs/kata-runtime that referenced this issue Nov 19, 2020

kata-runtime: Autospec creation for version 1.10.8

4a56c92

Fix tty issue in go 1.15.x golang/go#29458 creack/pty#96

omadawn mentioned this issue Dec 30, 2020

Setctty set but Ctty not valid in child google/goexpect#60

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syscall: ExtraFiles FD used to set controlling TTY instead of SysProcAttr.Ctty field #29458

syscall: ExtraFiles FD used to set controlling TTY instead of SysProcAttr.Ctty field #29458

sipsma commented Dec 29, 2018 •

edited

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sipsma commented Jun 25, 2019 •

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ianlancetaylor commented May 6, 2020

syscall: ExtraFiles FD used to set controlling TTY instead of SysProcAttr.Ctty field #29458

syscall: ExtraFiles FD used to set controlling TTY instead of SysProcAttr.Ctty field #29458

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sipsma commented Dec 29, 2018 • edited

What did you do?

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What did you see instead?

Does this issue reproduce with the latest release (go1.11.4)?

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sipsma commented Jun 25, 2019 • edited

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sipsma commented Jun 25, 2019 • edited

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sipsma commented Dec 29, 2018 •

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