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fix(transactions): restrict the save's temp file from creation; never remove another writer's - #164
Follow-up to #162, which merged at 02:17 UTC while Codex's last two review findings on its final commit were still unfixed. Both are real defects in the atomic save I added, so this fixes them. Rust only; no behaviour change outside the transaction-log save.
1. The temp file was readable before it was restricted. It was created with the umask default and took the log's restrictive mode only after the content was written, so for a log restricted to its owner (say 0600) another local user could read the new content through the temporary file during that window. The file now takes the replaced log's permissions at creation, while it is still empty.
2. Cleanup could delete another writer's live file. The temp name was PID plus a counter, and cleanup ran even when this save had not created the file. Writers in different PID namespaces that share a repository (containers on a shared volume) can pick the same name; the loser's cleanup then deleted the winner's live file and the winner's rename failed. The name now carries a random component, and only a file this call created is removed. If the create fails, the save fails cleanly with memory unchanged (it can be retried) and the other file is left alone.
Deliberately not changed
Codex's third finding on #162, that a directory-fsync error should fail the save, is still not taken. By then the rename has happened, so failing the save would leave disk on the new log and memory on the old one, the disagreement T-5 exists to remove. The sync stays best-effort, commented in the code and recorded in the ledger as not claimed. That thread was left open for the owner's decision and it is unchanged.
Tests and negative controls
the_temporary_file_is_restricted_before_any_content_is_written: a 0640 log's temp file is 0640 and still empty at creation. Mutant with the permissions applied after the write: fails (this test, and save_preserves_the_logs_permissions).
a_save_never_removes_a_temporary_file_it_did_not_create: a save onto a name already taken fails, leaves that file intact and writes no log. Mutant with unconditional cleanup: fails.
Each mutant was confirmed applied (diffed against the unmutated file) before its result was trusted.
Ledger and dashboards
T-5 gains two TESTED rows and its status-table row is updated. Dashboards: 132 → 134 tests (TOPOLOGY, READINESS), checked against cargo test --workspace --locked -- --list.
Verification
cargo fmt --all -- --check, cargo clippy --workspace --all-targets --locked -- -D warnings, cargo test --workspace --locked and tests/aspect/cross_cutting_test.sh (32 pass) are clean. dashboard-check locally shows only the same 10 Idris2 rows that fail because idris2 is not installed in this sandbox; CI's pinned image is the gate of record for those.
…and never remove another writer's
Two review findings on the atomic save (#162), found after it merged:
- The temporary file was created with the umask default and took the log's
restrictive mode only after the content was written, leaving a window in
which another local user could read a log restricted to its owner. The
file now takes the replaced log's permissions at creation, while empty.
- Cleanup removed the temporary path even when this save had not created it:
with PID-plus-counter names, writers in different PID namespaces sharing a
repository could pick the same name, and the loser deleted the winner's
live file. The name now carries a random component, and only a file this
call created is removed; a failed create leaves the path alone and fails
the save cleanly (memory unchanged, so it can be retried).
Tests: the_temporary_file_is_restricted_before_any_content_is_written and
a_save_never_removes_a_temporary_file_it_did_not_create, each checked
against a mutant (permissions after the write; unconditional cleanup).
Ledger T-5 gains two TESTED rows. Dashboards: 132 -> 134 tests.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Kjdf4Mf4Z41bNQh2TrsEp9
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Reviewing files that changed from the base of the PR and between 3b99d42 and 9560b61.
Files selected for processing: 4
PROOF-NEEDS.adoc
READINESS.adoc
TOPOLOGY.adoc
crates/reversible-core/src/transaction.rs
📝 Summary
Summary by CodeRabbit
Bug Fixes
Transaction-log saves now preserve the existing log’s permissions. If a save cannot create its temporary file, the existing log remains untouched.
Failed saves clean up only the temporary file created by that save, avoiding interference with another writer’s file. The log is replaced only after the new contents have been written and synced.
Transaction-log saves now use UUID-based sibling temporary files. The save copies available log permissions when it creates the temporary file, then writes and syncs before rename. Failure handling removes only temporary files created by that save. Tests and project records cover these changes.
Changes: Atomic transaction-log saves
Layer / File(s)
Summary
Temporary-file creation and atomic save crates/reversible-core/src/transaction.rs
Temporary paths now use UUID-based sibling names. Creation copies available destination permissions. The save writes and syncs before rename, and removes its own temporary file on failure.
Save tests and project records crates/reversible-core/src/transaction.rs, PROOF-NEEDS.adoc, READINESS.adoc, TOPOLOGY.adoc
Tests cover preserving an existing temporary file and copying permissions before writing. The claims ledger records these tests, and the readiness records report 134 tests.
hyperpolymath/januskey#162: This PR changes the temporary-file naming and save behaviour introduced by #162.
Merge Risk: Low · previous review 3b99d
The temporary transaction-log file is briefly created with default permissions before the log's permissions are applied, so the PR's claim that it is restricted at creation is not accurate. The exposure requires another local process with access to the directory and is a small confidentiality risk. Setting the mode at open time would close it, and it can be handled before or shortly after merge.
Pre-merge checks: 5
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Explanation
Title check
The title identifies the transaction save temporary-file permission and cleanup changes. It is concise and directly related to the main changes, although the wording is slightly awkward.
Description check
The description clearly explains both defects, the implemented fixes, the tests, the verification results, and the deliberately unchanged directory sync behaviour.
Docstring Coverage
Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Documentation-only edits and deletions within survi…
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Full details: Docstring Coverage
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Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 7 functions across 1 files. (3 skipped: 3 unsupported.)
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Inline comments:
Review comments at @crates/reversible-core/src/transaction.rs:
- Around line 131-134: Update the temporary-file creation in create_tmp to set
restrictive permissions with OpenOptionsExt::mode when opening the file, then
apply the existing log permissions before writing any content.
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PROOF-NEEDS.adoc
READINESS.adoc
TOPOLOGY.adoc
crates/reversible-core/src/transaction.rs
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GitHub Check: Reversibility as a grade (Loss instance), expected rejections
The previous commit applied the log's permissions right after creating the
temporary file, which still left an instant in which it had the umask
default. A local process that opened a read descriptor in that instant keeps
it across the later chmod and can read the content written afterwards, so
"restricted from creation" was not accurate.
On Unix the file is now opened with the log's mode (the umask can only clear
bits, so it is never more readable than the log), and the exact mode is then
set. Adds the_temporary_file_is_opened_with_the_logs_mode, checked against a
mutant that opens without the mode; it discriminates where the umask leaves
owner read-write (the usual 022), which the ledger row says.
Dashboards: 134 -> 135 tests.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Kjdf4Mf4Z41bNQh2TrsEp9
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What
Follow-up to #162, which merged at 02:17 UTC while Codex's last two review findings on its final commit were still unfixed. Both are real defects in the atomic save I added, so this fixes them. Rust only; no behaviour change outside the transaction-log save.
1. The temp file was readable before it was restricted. It was created with the umask default and took the log's restrictive mode only after the content was written, so for a log restricted to its owner (say
0600) another local user could read the new content through the temporary file during that window. The file now takes the replaced log's permissions at creation, while it is still empty.2. Cleanup could delete another writer's live file. The temp name was PID plus a counter, and cleanup ran even when this save had not created the file. Writers in different PID namespaces that share a repository (containers on a shared volume) can pick the same name; the loser's cleanup then deleted the winner's live file and the winner's rename failed. The name now carries a random component, and only a file this call created is removed. If the create fails, the save fails cleanly with memory unchanged (it can be retried) and the other file is left alone.
Deliberately not changed
Codex's third finding on #162, that a directory-
fsyncerror should fail the save, is still not taken. By then the rename has happened, so failing the save would leave disk on the new log and memory on the old one, the disagreement T-5 exists to remove. The sync stays best-effort, commented in the code and recorded in the ledger as not claimed. That thread was left open for the owner's decision and it is unchanged.Tests and negative controls
the_temporary_file_is_restricted_before_any_content_is_written: a0640log's temp file is0640and still empty at creation. Mutant with the permissions applied after the write: fails (this test, andsave_preserves_the_logs_permissions).a_save_never_removes_a_temporary_file_it_did_not_create: a save onto a name already taken fails, leaves that file intact and writes no log. Mutant with unconditional cleanup: fails.Ledger and dashboards
T-5 gains two TESTED rows and its status-table row is updated. Dashboards: 132 → 134 tests (TOPOLOGY, READINESS), checked against
cargo test --workspace --locked -- --list.Verification
cargo fmt --all -- --check,cargo clippy --workspace --all-targets --locked -- -D warnings,cargo test --workspace --lockedandtests/aspect/cross_cutting_test.sh(32 pass) are clean.dashboard-checklocally shows only the same 10 Idris2 rows that fail becauseidris2is not installed in this sandbox; CI's pinned image is the gate of record for those.Generated by Claude Code