[Bug 2134496] [NEW] readlink: traverse symlinks before resolving ..

[Benjamin Drung]

Public bug reported:

The readlink command from GNU coreutils and the one from uutil coreutils
behave differently in case the path contains symlinks and `..`. GNU
readlink traverses symlinks first, but uutils resolves `..` first.

Example from Ubuntu 25.10 (questing):

```sh
$ gnureadlink -f /sys/class/block/nvme0n1p1/..
/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/nvme/nvme0/nvme0n1
$ /usr/lib/cargo/bin/coreutils/readlink -f /sys/class/block/nvme0n1p1/..
/sys/class/block
```

This breaks dracut (see also https://github.com/dracut-ng/dracut-
ng/pull/1776).

** Affects: rust-coreutils
     Importance: Unknown
         Status: Unknown

** Affects: rust-coreutils (Ubuntu)
     Importance: Undecided
         Status: New

** Bug watch added: github.com/uutils/coreutils/issues #9057
   https://github.com/uutils/coreutils/issues/9057

** Also affects: rust-coreutils via
   https://github.com/uutils/coreutils/issues/9057
   Importance: Unknown
       Status: Unknown

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https://bugs.launchpad.net/bugs/2134496

Title:
  readlink: traverse symlinks before resolving ..

Status in rust-coreutils:
  Unknown
Status in rust-coreutils package in Ubuntu:
  New

Bug description:
  The readlink command from GNU coreutils and the one from uutil
  coreutils behave differently in case the path contains symlinks and
  `..`. GNU readlink traverses symlinks first, but uutils resolves `..`
  first.

  Example from Ubuntu 25.10 (questing):

  ```sh
  $ gnureadlink -f /sys/class/block/nvme0n1p1/..
  /sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/nvme/nvme0/nvme0n1
  $ /usr/lib/cargo/bin/coreutils/readlink -f /sys/class/block/nvme0n1p1/..
  /sys/class/block
  ```

  This breaks dracut (see also https://github.com/dracut-ng/dracut-
  ng/pull/1776).

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