Redact bounded env/shell wrapper command operands #907

Outcome

Sandbox command evidence redacts credentials inside supported wrapper operands without creating unbounded recursive parsing or masking benign command arguments.

Current defect

Draft #906 contains the direct Docker/Podman login -p, -p=, and --password= repair, but the current command-text path tokenizes only the outer command. Direct reproductions remain:

• env -S 'docker login -p <opaque>';
• sh -c 'podman login -p <opaque>';
• nested env → shell -c combinations.

The opaque credential survives because the wrapper operand is treated as ordinary data. Blindly calling the text and argv redactors recursively would instead create attacker-controlled recursion/CPU risk.

Required repair

• recognize only exact wrapper program basenames and exact option/operand positions:
  • env -S, env --split-string, and the long --split-string=... spelling;
  • sh, bash, dash, ksh, or zsh command strings selected by an exact/combined -c option;
• preserve the public APIs through private depth/context helpers and compile the literal matcher once at the public entry point;
• use MAX_COMMAND_WRAPPER_DEPTH = 4, MAX_COMMAND_INPUT_BYTES = 65_536, MAX_COMMAND_TOKENS = 4_096, and MAX_COMMAND_WORK = 262_144; share one UTF-8 byte/token/cumulative-work budget across the complete wrapper tree;
• at the depth bound, redact the entire remaining nested operand; at a root byte/token/work limit, fail closed for the complete public evidence;
• fail closed on malformed quoting/tokenization without publishing the raw nested operand or parser diagnostic;
• preserve executable argv, shell=False, environment, exit, timeout, process-group, and cleanup behavior;
• preserve benign env -u/--unset, env -C/--chdir, assignments, Docker publish-port -p 8080:80, and SSH port -p 22 diagnostics;
• keep the direct Docker/Podman fix and its runtime-synthesized fixtures.

Security design constraints

• Python shlex is not a semantic parser for either full shell -c input or GNU env -S; it may be used only after a linear quote-state scanner accepts a documented grammar subset.
• For every supported wrapper, backslashes, line breaks, an unquoted $, backtick, or #, and unclosed/unsupported quoting fail closed. For shell operands, unquoted control/operators such as ;, &&, ||, pipes, redirection, substitution, heredoc, parentheses, and glob/meta syntax also fail closed. Expansion inside double quotes is unsupported and fails closed.
• GNU env -S / --split-string has its own escape, comment, expansion, and trailing-argv behavior. Unsupported #, backslash forms (including \c), ${...}, or any trailing argv that could combine with the split operand fail closed for the complete command evidence.
• Shell -c following $0/positional argv must be preserved only under an explicitly proven mapping; otherwise the complete command evidence fails closed. A compound command such as sh -c 'echo ok; docker login -p <opaque>' must never be treated as one simple shlex command.
• Share one precompiled sensitive-value context and the single cumulative budget across every nested wrapper. Depth-only recursion, repeated full rescans, and repeated unbounded shlex.join expansion are forbidden.
• Malformed syntax, unsupported grammar, depth exhaustion, or budget exhaustion returns bounded redaction without raw text or exception details.
• Container-login detection is exact: the normalized program is Docker/Podman and command[1] == "login"; never infer the subcommand using membership elsewhere in argv.
• Fix and pin the current option false positives:
  • docker login --password-stdin registry preserves the registry because the option consumes stdin, not the following argv element;
  • --password-stdin=... remains conservatively redacted because it is not the valid no-argument form;
  • docker run --name login -p 8080:80 image and docker run login -p 8080:80 image preserve the publish port because an unrelated login argument is not the login subcommand.
• Preserve env -u/--unset/-C/--chdir values, ordinary assignments, Docker publish ports, and SSH ports.
• Cross-boundary fixtures cover JSON command fields containing wrappers and shell operands containing JSON; unsupported compositions fail closed.

Acceptance

• fail-first tests cover env -S, env --split-string, long = form, every listed shell basename and combined -c selector, env → shell nesting, malformed inner/outer quoting, compound shell syntax, env escapes/expansion/trailing argv, and a fixed ten-level nesting tree;
• boundary tests cover input UTF-8 bytes, total parsed tokens, cumulative scan work, maximum depth, and each limit plus one;
• negative tests prove benign env options/assignments, --password-stdin registry, unrelated login arguments, Docker publish ports, and SSH ports are byte-visible;
• direct Docker/Podman -p, -p=, and --password= credential cases remain redacted;
• all credential-shaped fixtures are synthesized at runtime; no fixed credential-shaped literal is committed;
• Sandbox Log Redaction Quality CI passes at the exact head with 100% statement/branch coverage for the three owned production modules;
• full suite, compile/docstring checks, Secret Scan over the full PR range, security/supply-chain gates, current source review, independent non-author approval, and protected-main stdout/stderr/timeout/service-tail canaries pass;
• Bound sandbox subprocess output and long-running service logs #766 remains the separate total-output/service-file resource-safety residual; this issue must not claim end-to-end output-memory closure;
• fix(sandbox): replay redaction after fixture-history contamination #906 remains Draft until this issue and the separate atomic-JSON boundary are either repaired or explicitly removed from its acceptance scope.

Related: #906, #908, #766.