[front] Fix sandbox function staging reads against symlink swap (TOCTOU) - #30191
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fontanierh wants to merge 2 commits into
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[front] Fix sandbox function staging reads against symlink swap (TOCTOU)#30191fontanierh wants to merge 2 commits into
fontanierh wants to merge 2 commits into
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buildSandboxFunctionOnSandbox and getDatabaseSchemaOnSandbox stage artifacts in agent-writable /tmp dirs as agent-proxied, then read them back through the provider file API, which envd serves as root while following symlinks. Code running as the agent on the same sandbox VM could swap a staging file for a symlink to a root-only file (e.g. /run/dust/egress-secrets.json) between the exec and the read, and the root read would return that file's content to the caller or persist it as a published function bundle. Pin each artifact to the sha256 captured at the end of the producing exec and fail closed on mismatch. A swap before the capture fails the capture itself (set -e: sha256sum cannot open the swapped target as agent-proxied); a swap after the capture no longer hashes equal. Error messages never carry content, so a swapped-in file cannot leak through the error path either.
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…sing hash Review feedback: anchor the stdout split on the last full-line marker so a model printing the marker string cannot shadow the real capture or truncate its own output mid-stream, and include the exec stderr in the missing-hash error so a failed capture (e.g. sha256sum denied on a swapped target) is debuggable.
zmarouf
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Aug 7, 2026
zmarouf
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LGTM. I tried poking and the only thing I found was the sha256sum format that GNU based.
But the check fails closed.
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Description
buildSandboxFunctionOnSandboxandgetDatabaseSchemaOnSandboxstage artifacts in agent-writable/tmpdirs asagent-proxied, then read them back through the provider file API, which envd serves as root while following symlinks. Code running as the agent on the same sandbox VM could swap a staging file for a symlink to a root-only file (e.g./run/dust/egress-secrets.json) between the exec and the read, and the root read would return that file's content to the caller or persist it as a published function bundle.Each producing exec now appends a marker and per-file sha256 lines after the dsbx output, and the read-back content is verified against those hashes before use, failing closed on any mismatch:
set -e;sha256sumcannot open the swapped target asagent-proxied)Follow-ups not in this PR: same hardening for any future
provider.readFile/writeFilecaller under agent-writable paths, and the dsbx port-80 Host pinning issue tracked separately.Tests
staging_integrity.test.tsfor the split/verify helpers.build_on_sandbox.test.tsand a newdsbx_db.test.tscovering the schema flow (match, swapped file, missing hash).lib/api/sandbox_functionsandlib/api/sandboxsuites pass locally in a dust-hive env (70 + 363 tests).Risk
Low. Only the two staging flows change; both fail closed on any anomaly (missing marker, missing hash, mismatch), so worst case is a failed publish/schema read that the model can retry. Rollback is a revert.
Deploy Plan
Standard deploy.