Block tilde expansion to prevent user info leak#2
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AlexandreYang merged 2 commits intomainfrom Mar 8, 2026
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Co-authored-by: AlexandreYang <49917914+AlexandreYang@users.noreply.github.com>
AlexandreYang
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Two Codex round-6 items, both real: 1. P1 — saturating block multiply. unix.Statfs_t.Blocks * bsize could wrap a uint64 if a buggy/malicious FUSE filesystem reports counts above MaxUint64/bsize, producing tiny/zero Total/Used/Free for that mount and corrupting the --total accumulation. Added a mulSat(a, b) helper to diskstats_unix.go that clamps to MaxUint64 on overflow. Linux and Darwin backends now use mulSat for Total, Free, and Used. Locked in by TestMulSat covering boundary, just-over-boundary, and the realistic FUSE-rogue (maxU * 4096) case. 2. P2 — last-flag-wins for -h / -H. The previous code unconditionally preferred -h, so `df -hH` (intended SI override) and shell aliases that append -H to a default got the wrong size column. pflag.Visit walks set flags in lexicographical order, not argv order, so it cannot be used to honor input order. Refactored to a custom unitFlag (a pflag.Value) where -h and -H share a single *unitMode target and each Set call overwrites it — the LAST one wins by construction. registerUnitFlag wraps fs.VarPF + NoOptDefVal="true" so the flags accept no argument, matching pflag's bool convention. Confirmed locally: `df -hH` prints SI (995G), `df -Hh` prints IEC (927G). New TestUnitFlag_LastFlagWins covers 10 argv interleavings including combined short flags (-hH, -Hh). Side effect of #2: dropped the unused `human`/`si` *bool fields from the flags struct and the resolveUnitMode helper; mode is now read directly from a *unitMode field. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
The upstream
mvdan.cc/sh/v3expand package callsos/user.Lookup()when it encounters~usernametilde expansion (e.g.,echo ~root). This leaks host system user home directories, bypassing the shell's sandbox. Since tilde is parsed as a plain*syntax.Lit(no dedicated AST node), the existing validator had no way to catch it.Changes
interp/validate.go: Added*syntax.Wordcheck invalidateNodethat rejects any unquoted word starting with~at the firstLitpart. Heredoc bodies are excluded via ahdocWordstracking set (heredocs don't undergo tilde expansion).SHELL_FEATURES.md: Updated tilde expansion entry to include~userform and note that it is rejected at validation (exit code 2).tilde_not_expanded.yamlandtilde_path_not_expanded.yamlnow expect exit code 2 (validation rejection) instead of runtime passthrough.tilde_username_blocked.yaml— verifies~rootis rejected (the critical security case)tilde_in_heredoc_allowed.yaml— verifies~in heredoc bodies still workstilde_in_variable_assignment_blocked.yaml— verifiesDIR=~/pathis rejectedtilde_quoted_allowed.yaml— verifies"~root"and'~/path'are allowed (no expansion in quotes)tilde_mid_word_allowed.yaml— verifiesfoo~baris allowed (not a tilde prefix)Testing
go build ./...— compiles cleanlygo test ./...— all tests pass (interp, cmd/rshell, scenario tests)go vet ./interp/...— no issuesgofmt— formattedPR by Bits
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