Public bug reported:

Expected behavior: symlinks handles paths such as /..

Actual behavior: symlinks crashes with SIGSEGV.

Steps to reproduce:

ln -s /.. mylink
symlinks .
Segmentation fault (core dumped)

Discussion: The parent directory of the root directory is just the root
directory. However, symlinks does not handle this case properly, leading
to a segmentation fault.

A minimal script to reproduce the crash is attached.

$ lsb_release -rd
Description:    Ubuntu 18.04.4 LTS
Release:        18.04

$ apt-cache policy symlinks
symlinks:
  Installed: 1.4-3build1
  Candidate: 1.4-3build1
  Version table:
 *** 1.4-3build1 500
        500 http://us.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status

** Affects: symlinks (Ubuntu)
     Importance: Undecided
         Status: New

** Attachment added: "reproduce.sh"
   
https://bugs.launchpad.net/bugs/1863521/+attachment/5328761/+files/reproduce.sh

** Description changed:

  Expected behavior: symlinks handles paths such as /..
  
- Actual behavior: symlinks crashes with SISEGV.
+ Actual behavior: symlinks crashes with SIGSEGV.
  
  Steps to reproduce:
  
  ln -s /.. mylink
  symlinks .
  Segmentation fault (core dumped)
  
  Discussion: The parent directory of the root directory is just the root
  directory. However, symlinks does not handle this case properly, leading
  to a segmentation fault.
  
  A minimal script to reproduce the crash is attached.
  
  $ lsb_release -rd
  Description:  Ubuntu 18.04.4 LTS
  Release:      18.04
  
  $ apt-cache policy symlinks
  symlinks:
-   Installed: 1.4-3build1
-   Candidate: 1.4-3build1
-   Version table:
-  *** 1.4-3build1 500
-         500 http://us.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
-         100 /var/lib/dpkg/status
+   Installed: 1.4-3build1
+   Candidate: 1.4-3build1
+   Version table:
+  *** 1.4-3build1 500
+         500 http://us.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
+         100 /var/lib/dpkg/status

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https://bugs.launchpad.net/bugs/1863521

Title:
  symlinks crashed with SIGSEGV in tidy_path() when path is /..

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