FA-11566 / Filesystem semantics / Open access

Readable directories are mistaken for searchable directories · case 01

Readable directories are mistaken for searchable directories.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Directory read permission is treated as permission to traverse a known child name.

VERIFIED REPAIR

Require execute/search permission on every traversed directory.

Unsuccessful approach: Checking only the immediate parent ignores blocked ancestors.

Case contract

Deterministic in-memory filesystem model. Given already-selected permission triples 0..7 for each ancestor, return whether a known file name can be traversed. Search bit 1 is needed at every ancestor; listing bit 4 is irrelevant. Empty ancestors succeeds.

Why this case matters

An offline semantic experiment for file API clients; it models only the stated operations, not a complete operating system.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(ancestors):
    return all(bits & 4 != 0 for bits in ancestors)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('search without listing',solve([1]*N),True)
check('readable but unsearchable',solve([4]),False)
check('blocked ancestor searchable parent',solve([0,1]),False)
check('blocked middle ancestor',solve([7,4,7]),False)
check('all permissions',solve([7]*N),True)
check('no ancestors',solve([]),True)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
search without listing	`False`	`True`	Failed
readable but unsearchable	`True`	`False`	Failed
blocked ancestor searchable parent	`False`	`False`	Passed
blocked middle ancestor	`True`	`False`	Failed
all permissions	`True`	`True`	Passed
no ancestors	`True`	`True`	Passed

SHA-256 / c20456c5c565419709e8aa3e9a382b6231eb6a7ae01d4bd17e3d72550b7dff18

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(ancestors):
    return not ancestors or bool(ancestors[-1]&1)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('search without listing',solve([1]*N),True)
check('readable but unsearchable',solve([4]),False)
check('blocked ancestor searchable parent',solve([0,1]),False)
check('blocked middle ancestor',solve([7,4,7]),False)
check('all permissions',solve([7]*N),True)
check('no ancestors',solve([]),True)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
search without listing	`True`	`True`	Passed
readable but unsearchable	`False`	`False`	Passed
blocked ancestor searchable parent	`True`	`False`	Failed
blocked middle ancestor	`True`	`False`	Failed
all permissions	`True`	`True`	Passed
no ancestors	`True`	`True`	Passed

SHA-256 / df9a77dd1ab118b603824ddc192908a5d60def1aa7e8f7a86400e53623a1966b

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(ancestors):
    return all(bits & 1 != 0 for bits in ancestors)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('search without listing',solve([1]*N),True)
check('readable but unsearchable',solve([4]),False)
check('blocked ancestor searchable parent',solve([0,1]),False)
check('blocked middle ancestor',solve([7,4,7]),False)
check('all permissions',solve([7]*N),True)
check('no ancestors',solve([]),True)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
search without listing	`True`	`True`	Passed
readable but unsearchable	`False`	`False`	Passed
blocked ancestor searchable parent	`False`	`False`	Passed
blocked middle ancestor	`False`	`False`	Passed
all permissions	`True`	`True`	Passed
no ancestors	`True`	`True`	Passed

SHA-256 / 103ad69efd42a812da2a93b2ac2daa3ab469b35146147c6d1ab57bceacfea139

Verification & scope

This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:38:49.093353+00:00.

Case digest / 0ab270c25e87cd3d9e1c3c69f54049d10abd073bcad1ac6732acd3772c285d5f