Is it possible to change the process on the master or slave side of a pseudoterminal pair?
Clash Royale CLAN TAG#URR8PPP
0
Given a pair of pseudoterminal master and slave, and two processes communicating via them,
- is it possible to change the process on the master side to another process?
- is it possible to change the process on the slave side to another process?
My questions comes from 炸鱼薯条德里克's comment at Can ssh client connect to an existing shell running on a remote machine?
How is the SSH server "connect" to a shell session? It holds the master pty fd and ensure shell use the corresponding slave pty fd as its stdin/stdout/stderr. Does any SSH server provide the functionality of stealing out the corresponding master pty fd of a already running shell session? I don't think so.
Thanks.
pseudoterminal
asked Mar 1 at 13:29
TimTim
28.3k78269490
|
show 1 more comment
0
Given a pair of pseudoterminal master and slave, and two processes communicating via them,
- is it possible to change the process on the master side to another process?
- is it possible to change the process on the slave side to another process?
My questions comes from 炸鱼薯条德里克's comment at Can ssh client connect to an existing shell running on a remote machine?
How is the SSH server "connect" to a shell session? It holds the master pty fd and ensure shell use the corresponding slave pty fd as its stdin/stdout/stderr. Does any SSH server provide the functionality of stealing out the corresponding master pty fd of a already running shell session? I don't think so.
Thanks.
pseudoterminal
asked Mar 1 at 13:29
TimTim
28.3k78269490
A process holding fd to them, not the process of them. Two processes are possible to hold fds to the same open file description, and so the same pty. I think it's possible, for example, if these processes holding these fds allow you to communicate with them through UNIX domain socket and pass you that fd, then you can get these fd. Or simplyptrace()to the process and steal these fd out. But I have no experience ofptrace()at all.
– 炸鱼薯条德里克
Mar 1 at 13:48
Yes and yes. Of course, it's hacky (you should use a debugger) and you need the right permissions; for the case of ssh, the master side is held by a process running as root. In a script I wrote for one of your question, I was calling ptsname() on the master side of a pty to get the name of its slave side; instead of calling ptsname(), you can call read() or write().
– mosvy
Mar 1 at 13:49
It's just normally distro setup the kernel that disallow you to steal other process's fd, and most program wouldn't provide such functionality of giving out fd by UDS.
– 炸鱼薯条德里克
Mar 1 at 13:51
@炸鱼薯条德里克 It's not a "distro thing", it's a permission thing. You have to either have CAP_SYS_PTRACE or be the same user in order to attach to another process and "steal" its fds via SCM_RIGHTS (or simply run ops on them in the context of that process).
– mosvy
Mar 1 at 13:55
1
@炸鱼薯条德里克 I never had to turn any switch in order to be able to send fds via SCM_RIGHTS ancillary messages; and if you attach to a process with ptrace(), you can run any command in the context of that process, including sending fds via a UNIX socket.
– mosvy
Mar 1 at 14:02
|
show 1 more comment
0
0
0
Given a pair of pseudoterminal master and slave, and two processes communicating via them,
- is it possible to change the process on the master side to another process?
- is it possible to change the process on the slave side to another process?
My questions comes from 炸鱼薯条德里克's comment at Can ssh client connect to an existing shell running on a remote machine?
How is the SSH server "connect" to a shell session? It holds the master pty fd and ensure shell use the corresponding slave pty fd as its stdin/stdout/stderr. Does any SSH server provide the functionality of stealing out the corresponding master pty fd of a already running shell session? I don't think so.
Thanks.
pseudoterminal
asked Mar 1 at 13:29
TimTim
28.3k78269490
Given a pair of pseudoterminal master and slave, and two processes communicating via them,
- is it possible to change the process on the master side to another process?
- is it possible to change the process on the slave side to another process?
My questions comes from 炸鱼薯条德里克's comment at Can ssh client connect to an existing shell running on a remote machine?
How is the SSH server "connect" to a shell session? It holds the master pty fd and ensure shell use the corresponding slave pty fd as its stdin/stdout/stderr. Does any SSH server provide the functionality of stealing out the corresponding master pty fd of a already running shell session? I don't think so.
Thanks.
pseudoterminal
pseudoterminal
asked Mar 1 at 13:29
TimTim
28.3k78269490
asked Mar 1 at 13:29
TimTim
28.3k78269490
asked Mar 1 at 13:29
TimTim
28.3k78269490
asked Mar 1 at 13:29
TimTim
28.3k78269490
asked Mar 1 at 13:29
TimTim
28.3k78269490
28.3k78269490
A process holding fd to them, not the process of them. Two processes are possible to hold fds to the same open file description, and so the same pty. I think it's possible, for example, if these processes holding these fds allow you to communicate with them through UNIX domain socket and pass you that fd, then you can get these fd. Or simplyptrace()to the process and steal these fd out. But I have no experience ofptrace()at all.
– 炸鱼薯条德里克
Mar 1 at 13:48
Yes and yes. Of course, it's hacky (you should use a debugger) and you need the right permissions; for the case of ssh, the master side is held by a process running as root. In a script I wrote for one of your question, I was calling ptsname() on the master side of a pty to get the name of its slave side; instead of calling ptsname(), you can call read() or write().
– mosvy
Mar 1 at 13:49
It's just normally distro setup the kernel that disallow you to steal other process's fd, and most program wouldn't provide such functionality of giving out fd by UDS.
– 炸鱼薯条德里克
Mar 1 at 13:51
@炸鱼薯条德里克 It's not a "distro thing", it's a permission thing. You have to either have CAP_SYS_PTRACE or be the same user in order to attach to another process and "steal" its fds via SCM_RIGHTS (or simply run ops on them in the context of that process).
– mosvy
Mar 1 at 13:55
1
@炸鱼薯条德里克 I never had to turn any switch in order to be able to send fds via SCM_RIGHTS ancillary messages; and if you attach to a process with ptrace(), you can run any command in the context of that process, including sending fds via a UNIX socket.
– mosvy
Mar 1 at 14:02
|
show 1 more comment
A process holding fd to them, not the process of them. Two processes are possible to hold fds to the same open file description, and so the same pty. I think it's possible, for example, if these processes holding these fds allow you to communicate with them through UNIX domain socket and pass you that fd, then you can get these fd. Or simplyptrace()to the process and steal these fd out. But I have no experience ofptrace()at all.
– 炸鱼薯条德里克
Mar 1 at 13:48
Yes and yes. Of course, it's hacky (you should use a debugger) and you need the right permissions; for the case of ssh, the master side is held by a process running as root. In a script I wrote for one of your question, I was calling ptsname() on the master side of a pty to get the name of its slave side; instead of calling ptsname(), you can call read() or write().
– mosvy
Mar 1 at 13:49
It's just normally distro setup the kernel that disallow you to steal other process's fd, and most program wouldn't provide such functionality of giving out fd by UDS.
– 炸鱼薯条德里克
Mar 1 at 13:51
@炸鱼薯条德里克 It's not a "distro thing", it's a permission thing. You have to either have CAP_SYS_PTRACE or be the same user in order to attach to another process and "steal" its fds via SCM_RIGHTS (or simply run ops on them in the context of that process).
– mosvy
Mar 1 at 13:55
1
@炸鱼薯条德里克 I never had to turn any switch in order to be able to send fds via SCM_RIGHTS ancillary messages; and if you attach to a process with ptrace(), you can run any command in the context of that process, including sending fds via a UNIX socket.
– mosvy
Mar 1 at 14:02
A process holding fd to them, not the process of them. Two processes are possible to hold fds to the same open file description, and so the same pty. I think it's possible, for example, if these processes holding these fds allow you to communicate with them through UNIX domain socket and pass you that fd, then you can get these fd. Or simply
ptrace() to the process and steal these fd out. But I have no experience of ptrace() at all.– 炸鱼薯条德里克
Mar 1 at 13:48
A process holding fd to them, not the process of them. Two processes are possible to hold fds to the same open file description, and so the same pty. I think it's possible, for example, if these processes holding these fds allow you to communicate with them through UNIX domain socket and pass you that fd, then you can get these fd. Or simply
ptrace() to the process and steal these fd out. But I have no experience of ptrace() at all.– 炸鱼薯条德里克
Mar 1 at 13:48
Yes and yes. Of course, it's hacky (you should use a debugger) and you need the right permissions; for the case of ssh, the master side is held by a process running as root. In a script I wrote for one of your question, I was calling ptsname() on the master side of a pty to get the name of its slave side; instead of calling ptsname(), you can call read() or write().
– mosvy
Mar 1 at 13:49
Yes and yes. Of course, it's hacky (you should use a debugger) and you need the right permissions; for the case of ssh, the master side is held by a process running as root. In a script I wrote for one of your question, I was calling ptsname() on the master side of a pty to get the name of its slave side; instead of calling ptsname(), you can call read() or write().
– mosvy
Mar 1 at 13:49
It's just normally distro setup the kernel that disallow you to steal other process's fd, and most program wouldn't provide such functionality of giving out fd by UDS.
– 炸鱼薯条德里克
Mar 1 at 13:51
It's just normally distro setup the kernel that disallow you to steal other process's fd, and most program wouldn't provide such functionality of giving out fd by UDS.
– 炸鱼薯条德里克
Mar 1 at 13:51
@炸鱼薯条德里克 It's not a "distro thing", it's a permission thing. You have to either have CAP_SYS_PTRACE or be the same user in order to attach to another process and "steal" its fds via SCM_RIGHTS (or simply run ops on them in the context of that process).
– mosvy
Mar 1 at 13:55
@炸鱼薯条德里克 It's not a "distro thing", it's a permission thing. You have to either have CAP_SYS_PTRACE or be the same user in order to attach to another process and "steal" its fds via SCM_RIGHTS (or simply run ops on them in the context of that process).
– mosvy
Mar 1 at 13:55
1
1
@炸鱼薯条德里克 I never had to turn any switch in order to be able to send fds via SCM_RIGHTS ancillary messages; and if you attach to a process with ptrace(), you can run any command in the context of that process, including sending fds via a UNIX socket.
– mosvy
Mar 1 at 14:02
@炸鱼薯条德里克 I never had to turn any switch in order to be able to send fds via SCM_RIGHTS ancillary messages; and if you attach to a process with ptrace(), you can run any command in the context of that process, including sending fds via a UNIX socket.
– mosvy
Mar 1 at 14:02
|
show 1 more comment
0
active
oldest
votes
Your Answer
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "106"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
draft saved
draft discarded
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f503785%2fis-it-possible-to-change-the-process-on-the-master-or-slave-side-of-a-pseudoterm%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
0
active
oldest
votes
0
active
oldest
votes
active
oldest
votes
active
oldest
votes
draft saved
draft discarded
Thanks for contributing an answer to Unix & Linux Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
draft saved
draft discarded
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f503785%2fis-it-possible-to-change-the-process-on-the-master-or-slave-side-of-a-pseudoterm%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
A process holding fd to them, not the process of them. Two processes are possible to hold fds to the same open file description, and so the same pty. I think it's possible, for example, if these processes holding these fds allow you to communicate with them through UNIX domain socket and pass you that fd, then you can get these fd. Or simply
ptrace()to the process and steal these fd out. But I have no experience ofptrace()at all.– 炸鱼薯条德里克
Mar 1 at 13:48
Yes and yes. Of course, it's hacky (you should use a debugger) and you need the right permissions; for the case of ssh, the master side is held by a process running as root. In a script I wrote for one of your question, I was calling ptsname() on the master side of a pty to get the name of its slave side; instead of calling ptsname(), you can call read() or write().
– mosvy
Mar 1 at 13:49
It's just normally distro setup the kernel that disallow you to steal other process's fd, and most program wouldn't provide such functionality of giving out fd by UDS.
– 炸鱼薯条德里克
Mar 1 at 13:51
@炸鱼薯条德里克 It's not a "distro thing", it's a permission thing. You have to either have CAP_SYS_PTRACE or be the same user in order to attach to another process and "steal" its fds via SCM_RIGHTS (or simply run ops on them in the context of that process).
– mosvy
Mar 1 at 13:55
1
@炸鱼薯条德里克 I never had to turn any switch in order to be able to send fds via SCM_RIGHTS ancillary messages; and if you attach to a process with ptrace(), you can run any command in the context of that process, including sending fds via a UNIX socket.
– mosvy
Mar 1 at 14:02