| 1 | //go:build unix |
| 2 | |
| 3 | package activator |
| 4 | |
| 5 | import ( |
| 6 | "errors" |
| 7 | "os" |
| 8 | "syscall" |
| 9 | |
| 10 | "golang.org/x/sys/unix" |
| 11 | ) |
| 12 | |
| 13 | // openOwnEnvNoFollow opens a flat row's own env file (<host>.env, or its |
| 14 | // sibling <host>.config.env) and refuses, in the open itself, what a |
| 15 | // same-uid sibling (spec §7.2) could have planted at the name: a symlink, |
| 16 | // by O_NOFOLLOW; and a FIFO or a device, by opening O_NONBLOCK (so the open |
| 17 | // never waits for a writer that will not come) and then accepting only a |
| 18 | // regular file from fstat. There is no window between a check and the |
| 19 | // open. A refused link is the bare errOwnEnvSymlink and a refused non-file |
| 20 | // the bare errOwnEnvNotRegular: the caller names the path, once. The |
| 21 | // descriptor is handed back blocking: a regular file never blocks, and the |
| 22 | // appends and fsyncs that follow want ordinary semantics. A nested row's |
| 23 | // file needs none of this: instancefs.OpenBeneath does the same with |
| 24 | // openat2. |
| 25 | func openOwnEnvNoFollow(path string, flag int, perm os.FileMode) (*os.File, error) { |
| 26 | f, err := os.OpenFile(path, flag|unix.O_NOFOLLOW|unix.O_NONBLOCK, perm) |
| 27 | if errors.Is(err, unix.ELOOP) { |
| 28 | return nil, errOwnEnvSymlink |
| 29 | } |
| 30 | if err != nil { |
| 31 | return nil, err |
| 32 | } |
| 33 | st, err := f.Stat() |
| 34 | if err != nil { |
| 35 | f.Close() |
| 36 | return nil, err |
| 37 | } |
| 38 | if !st.Mode().IsRegular() { |
| 39 | f.Close() |
| 40 | return nil, errOwnEnvNotRegular |
| 41 | } |
| 42 | if err := syscall.SetNonblock(int(f.Fd()), false); err != nil { |
| 43 | f.Close() |
| 44 | return nil, err |
| 45 | } |
| 46 | return f, nil |
| 47 | } |
| 48 | |
amadan