fix(entrypoint): bind-mount passwd/group synthesis fallback for read-only /host/etc (ARC/DinD) by Copilot · Pull Request #4831 · github/gh-aw-firewall

Copilot · 2026-06-12T19:56:34Z

On ARC/DinD runners the Docker daemon's root filesystem is often read-only or tmpfs-backed, so entrypoint.sh's runtime identity synthesis silently failed when appending to /host/etc/passwd and /host/etc/group. This caused capsh to fall back to numeric UID/GID — breaking threat-detection and requiring consumers to pre-seed the daemon's /etc/passwd as a workaround.

Changes

`containers/agent/entrypoint.sh`

When appending to /host/etc/passwd (or /host/etc/group) fails (EROFS), falls back to:
1. Copying the existing file to /tmp/awf-etc/
2. Appending the synthesized entry to the writable copy
3. mount --binding the copy over the read-only original
CAP_SYS_ADMIN is still held at this point in the entrypoint (dropped by capsh just before user code runs), so the bind-mount succeeds. The mount is container-scoped and cleaned up on exit.
```
# read-only fallback path (new)
SYNTH_ETC_DIR="/tmp/awf-etc"
mkdir -p "${SYNTH_ETC_DIR}"
cp /host/etc/passwd "${SYNTH_ETC_DIR}/passwd"
echo "${PASSWD_ENTRY}" >> "${SYNTH_ETC_DIR}/passwd"
chmod 644 "${SYNTH_ETC_DIR}/passwd"
mount --bind "${SYNTH_ETC_DIR}/passwd" /host/etc/passwd
```

`docs/chroot-mode.md`

Updated the DinD Identity Synthesis section to describe the bind-mount fallback and the capability dependency.

When entrypoint.sh cannot append to /host/etc/passwd or /host/etc/group because the filesystem is read-only (ARC/DinD with tmpfs-backed daemon root), copy the existing file to /tmp/awf-etc/ and bind-mount it over the read-only original after appending the synthesized entry. CAP_SYS_ADMIN is still held at entrypoint time (dropped by capsh before user code runs), so mount --bind succeeds. This replaces the [WARN] + continue path that caused downstream capsh identity resolution failures. Also update docs/chroot-mode.md to describe the new bind-mount fallback. Closes #4829

github-actions · 2026-06-12T21:23:56Z

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Pull request overview

This PR improves chroot-mode identity synthesis on ARC/DinD runners by adding a bind-mount fallback when /host/etc/passwd and /host/etc/group are read-only, preventing capsh from falling back to numeric UID/GID and breaking identity-dependent features.

Changes:

Add a read-only fallback path in containers/agent/entrypoint.sh that writes synthesized passwd/group entries to /tmp/awf-etc/ and bind-mounts them over /host/etc/*.
Update chroot-mode documentation to describe the new bind-mount fallback and its CAP_SYS_ADMIN dependency.

Show a summary per file

File	Description
containers/agent/entrypoint.sh	Adds bind-mount fallback for passwd/group synthesis when `/host/etc` is read-only in ARC/DinD.
docs/chroot-mode.md	Documents the new runtime bind-mount fallback behavior and capability requirement.

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github-actions · 2026-06-12T21:34:54Z

🔬 Smoke Test Results — Auth mode: PAT (COPILOT_GITHUB_TOKEN)

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PR: fix(entrypoint): bind-mount passwd/group synthesis fallback for read-only /host/etc (ARC/DinD)
Author: @Copilot | Assignees: @lpcox, @Copilot

Overall: ✅ PASS

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github-actions · 2026-06-12T21:35:23Z

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github-actions · 2026-06-12T21:35:42Z

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Smoke Test Results

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GitHub.com HTTP	❌ (template vars unresolved)
File write/read	❌ (template vars unresolved)

Overall: FAIL — workflow template variables (steps.smoke-data.outputs.*) were not substituted; pre-computed data unavailable.

PR: fix(entrypoint): bind-mount passwd/group synthesis fallback for read-only /host/etc (ARC/DinD)
Author: @Copilot | Assignees: @lpcox @Copilot

Note

🔒 Integrity filter blocked 1 item

The following item was blocked because it doesn't meet the GitHub integrity level.

#4828 list_pull_requests: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".

To allow these resources, lower min-integrity in your GitHub frontmatter:

tools:
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github-actions · 2026-06-12T21:38:07Z

🏗️ Build Test Suite Results

Ecosystem	Project	Build/Install	Tests	Status
Bun	elysia	✅	1/1 passed	✅ PASS
Bun	hono	✅	1/1 passed	✅ PASS
C++	fmt	✅	N/A	✅ PASS
C++	json	✅	N/A	✅ PASS
Deno	oak	N/A	1/1 passed	✅ PASS
Deno	std	N/A	1/1 passed	✅ PASS
.NET	hello-world	✅	N/A	✅ PASS
.NET	json-parse	✅	N/A	✅ PASS
Go	color	✅	1/1 passed	✅ PASS
Go	env	✅	1/1 passed	✅ PASS
Go	uuid	✅	1/1 passed	✅ PASS
Java	gson	✅	1/1 passed	✅ PASS
Java	caffeine	✅	1/1 passed	✅ PASS
Node.js	clsx	✅	all passed	✅ PASS
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Node.js	p-limit	✅	all passed	✅ PASS
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Overall: 8/8 ecosystems passed — ✅ PASS

Generated by Build Test Suite for issue #4831 · ◷

github-actions · 2026-06-12T21:39:03Z

Smoke Test: GitHub Actions Services Connectivity

Check	Result
Redis PING	❌ Timeout/no response
PostgreSQL pg_isready	❌ No response on port 5432
PostgreSQL SELECT 1	❌ Timeout/no response

Overall: FAIL — host.docker.internal services are not reachable from this environment.

🔌 Service connectivity validated by Smoke Services

github-actions · 2026-06-12T21:39:46Z

@Copilot @lpcox

GitHub MCP: ✅
GitHub.com HTTP: ✅ (200)
Agent file I/O: ✅ ("agent-write-check")
Direct BYOK inference mode via api-proxy → Azure OpenAI (Foundry, o4-mini-aw): ✅

Overall: PASS

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Copilot AI linked an issue Jun 12, 2026 that may be closed by this pull request

[ARC/DinD] Passwd synthesis hard-fails on read-only /host/etc (v0.25.65+) #4829

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Copilot AI changed the title ~~[WIP] Fix passwd synthesis hard-fail on read-only /host/etc~~ fix(entrypoint): bind-mount passwd/group synthesis fallback for read-only /host/etc (ARC/DinD) Jun 12, 2026

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fix(entrypoint): bind-mount passwd/group synthesis fallback for read-only /host/etc (ARC/DinD)#4831

fix(entrypoint): bind-mount passwd/group synthesis fallback for read-only /host/etc (ARC/DinD)#4831
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