mkfifo: permissions of an existing file are changed after FIFO creation fails

When mkfifo() fails (e.g. target already exists), the code shows an error but is missing a continue;, so it falls through to fs::set_permissions and changes the permissions of the pre-existing file to the default FIFO mode (0o666 & umask -> 0644).

$ touch secret; chmod 000 secret
$ coreutils mkfifo secret fifo3 fifo4
mkfifo: cannot create fifo 'secret': File exists
$ ll secret      # uutils:
prw-r--r-- secret   # changed to 644 (GNU leaves it 000)

Impact: an attacker (or user error) can relax permissions on sensitive owner-only files such as SSH private keys, exposing them to other users. Recommendation: add continue; after the error.

Remediation: Acknowledged by Canonical; fixed in PR #10376.

Reported by Zellic in the uutils coreutils Program Security Assessment (prepared for Canonical, Jan 20 2026), audited commit 3a07ffc5a9bd4c283e75afa548ba1f1957bad242. Finding 3.8. Credit: Zellic.

Upstream tracking issue: https://github.com/uutils/coreutils/issues/10020 · CVE-2026-35341