From 54294640194fa659af63b3848a4be43587bb206a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Aur=C3=A9lien=20Bombo?= <abombo@microsoft.com>
Date: Mon, 22 Sep 2025 18:06:40 -0500
Subject: [PATCH] agent/rustjail: Fix double free in TTY handling
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The repro below would show this error in the logs (in debug mode only):

  fatal runtime error: IO Safety violation: owned file descriptor already closed

The issue was that the `pseudo.slave` file descriptor was being owned by
multiple variables simultaneously. When any of those variables would go out
of scope, they would close the same file descriptor, which is undefined
behavior.

To fix this, we clone: we create a new file descriptOR that refers to the same
file descriptION as the original. When the cloned descriptor is closed, this
affect neither the original descriptor nor the description.  Only when the last
descriptor is closed does the kernel cleans up the description.

Note that we purposely consume (not clone) the original descriptor with
`child_stdin` as `pseudo` is NOT dropped automatically.

Repro
-----

Prerequisites:
 - Use Rust 1.80+.
 - Build the agent in debug mode.

$ cat busybox.yaml
apiVersion: v1
kind: Pod
metadata:
  name: busybox
spec:
  containers:
  - image: busybox:latest
    name: busybox
  runtimeClassName: kata

$ kubectl apply -f busyboox.yaml
pod/busybox created

$ kubectl exec -it busybox -- sh
error: Internal error occurred: Internal error occurred: error executing
command in container: failed to exec in container: failed to start exec
"e6c602352849647201860c1e1888d99ea3166512f1cc548b9d7f2533129508a9":
cannot enter container 76a499cbf747b9806689e51f6ba35e46d735064a3f176f9be034777e93a242d5,
with err ttrpc: closed

Fixes: #11054

Signed-off-by: Aurélien Bombo <abombo@microsoft.com>
---
 src/agent/rustjail/src/container.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/agent/rustjail/src/container.rs b/src/agent/rustjail/src/container.rs
index 291f19af1f..1fb05260e3 100644
--- a/src/agent/rustjail/src/container.rs
+++ b/src/agent/rustjail/src/container.rs
@@ -1045,8 +1045,8 @@ impl BaseContainer for LinuxContainer {
                 .map_err(|e| warn!(logger, "fcntl pseudo.slave {:?}", e));
 
             child_stdin = unsafe { std::process::Stdio::from_raw_fd(pseudo.slave) };
-            child_stdout = unsafe { std::process::Stdio::from_raw_fd(pseudo.slave) };
-            child_stderr = unsafe { std::process::Stdio::from_raw_fd(pseudo.slave) };
+            child_stdout = unsafe { std::process::Stdio::from_raw_fd(unistd::dup(pseudo.slave)?) };
+            child_stderr = unsafe { std::process::Stdio::from_raw_fd(unistd::dup(pseudo.slave)?) };
 
             if let Some(proc_io) = &mut p.proc_io {
                 // A reference count used to clean up the term master fd.