Switching from canonical to non-canonical mode in a PTY can cause EOF when reading

[Nathan Wang]

Description

I think this line of code:

gvisor/pkg/sentry/fsimpl/devpts/line_discipline.go

Line 157 in 2c8e77f

 l.inQueue.readable = true 

should be len(l.inQueue.buffer) > 0 rather than true. Otherwise, it seems like switching from canonical to non-canonical mode in a PTY, then reading from the input, could cause an EOF. Making this change fixes my reproduction below, but I'm quite new to this codebase so perhaps I'm mistaken about what's going on.

Steps to reproduce

Install IPython and create a Python file:

import IPython
IPython.embed()

Run this Python file within a pty. One option might be import pty; pty.spawn(["python", "main.py"])

Press question mark + enter a few times; you should see an EOF error.

runsc version

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docker version (if using docker)

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uname

Linux ip-10-1-5-239 5.15.0-1048-aws #53~20.04.1-Ubuntu SMP Wed Oct 4 16:44:20 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

kubectl (if using Kubernetes)

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repo state (if built from source)

release-20240122.0-27-gac416763d

runsc debug logs (if available)

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