| 1 | //go:build !windows && !plan9 |
| 2 | |
| 3 | package fileutil |
| 4 | |
| 5 | import ( |
| 6 | "fmt" |
| 7 | "os" |
| 8 | "path/filepath" |
| 9 | "strings" |
| 10 | "syscall" |
| 11 | ) |
| 12 | |
| 13 | // OpenFileBeneath opens rel first, validates the identity held by that open |
| 14 | // descriptor against a resolved path beneath root, then returns the same |
| 15 | // descriptor for reading. A concurrent symlink or directory swap either fails |
| 16 | // the identity check or happens after the descriptor has pinned the safe file. |
| 17 | func OpenFileBeneath(root, rel string) (*os.File, error) { |
| 18 | root = filepath.Clean(strings.TrimSpace(root)) |
| 19 | if root == "" || root == "." { |
| 20 | return nil, fmt.Errorf("workspace root is empty") |
| 21 | } |
| 22 | rel, err := confinedRelativePath(rel) |
| 23 | if err != nil { |
| 24 | return nil, err |
| 25 | } |
| 26 | rootFile, err := os.Open(root) |
| 27 | if err != nil { |
| 28 | return nil, fmt.Errorf("open workspace root: %w", err) |
| 29 | } |
| 30 | defer rootFile.Close() |
| 31 | openedRoot, err := rootFile.Stat() |
| 32 | if err != nil { |
| 33 | return nil, fmt.Errorf("stat workspace root: %w", err) |
| 34 | } |
| 35 | abs := filepath.Join(root, rel) |
| 36 | // O_NONBLOCK prevents a workspace FIFO from stalling admission before the |
| 37 | // caller can inspect and reject its descriptor type. It is inert for regular |
| 38 | // files, which are the only pinned-context targets accepted by the caller. |
| 39 | file, err := os.OpenFile(abs, os.O_RDONLY|syscall.O_NONBLOCK, 0) |
| 40 | if err != nil { |
| 41 | return nil, err |
| 42 | } |
| 43 | fail := func(err error) (*os.File, error) { |
| 44 | _ = file.Close() |
| 45 | return nil, err |
| 46 | } |
| 47 | opened, err := file.Stat() |
| 48 | if err != nil { |
| 49 | return fail(err) |
| 50 | } |
| 51 | resolvedRoot, err := filepath.EvalSymlinks(root) |
| 52 | if err != nil { |
| 53 | return fail(fmt.Errorf("resolve workspace root: %w", err)) |
| 54 | } |
| 55 | currentRoot, err := os.Stat(resolvedRoot) |
| 56 | if err != nil { |
| 57 | return fail(fmt.Errorf("stat resolved workspace root: %w", err)) |
| 58 | } |
| 59 | if !os.SameFile(openedRoot, currentRoot) { |
| 60 | return fail(fmt.Errorf("workspace root changed while file was being opened")) |
| 61 | } |
| 62 | resolvedTarget, err := filepath.EvalSymlinks(abs) |
| 63 | if err != nil { |
| 64 | return fail(fmt.Errorf("resolve workspace file: %w", err)) |
| 65 | } |
| 66 | resolvedRel, err := filepath.Rel(resolvedRoot, resolvedTarget) |
| 67 | if err != nil || resolvedRel == ".." || strings.HasPrefix(resolvedRel, ".."+string(filepath.Separator)) { |
| 68 | return fail(fmt.Errorf("file resolves outside workspace root")) |
| 69 | } |
| 70 | current, err := os.Stat(resolvedTarget) |
| 71 | if err != nil { |
| 72 | return fail(err) |
| 73 | } |
| 74 | if !os.SameFile(opened, current) { |
| 75 | return fail(fmt.Errorf("workspace path changed while it was being opened")) |
| 76 | } |
| 77 | return file, nil |
| 78 | } |
| 79 |