Chapter 5. Issues to be aware of for stretch

Table of Contents

5.1. Upgrade specific items for Stretch
5.1.1. Late mounting of /usr is no longer supported
5.1.2. Noteworthy obsolete packages
5.1.3. Deprecated components for Stretch
5.1.4. Things to do post upgrade before rebooting
5.1.5. Executables are now compiled as position independent executables (PIE) by default
5.2. Limitations in security support
5.2.1. Security status of web browsers
5.2.2. Lack of security support for the ecosystem around libv8 and Node.js
5.3. Package specific issues
5.3.1. Older ciphers and SSH1 protocol disabled in OpenSSH by default
5.3.2. Possible backwards incompatible changes to APT
5.3.3. The Xorg server is no longer setuid root by default
5.3.4. Upstart removed
5.3.5. The debhelper tool now generates dbgsym packages by default

Sometimes, changes introduced in a new release have side-effects we cannot reasonably avoid, or they expose bugs somewhere else. This section documents issues we are aware of. Please also read the errata, the relevant packages' documentation, bug reports and other information mentioned in Section 6.1, “Further reading”.

5.1. Upgrade specific items for Stretch

This section covers items related to the upgrade from Jessie to Stretch

5.1.1. Late mounting of /usr is no longer supported

[Note]Note

This section only applies to systems using a custom kernel, where /usr is on a separate mount point from /. If you use the kernel packages provided by Debian, you are unaffected by this issue.

Mounting of /usr using only tools found in / is no longer supported. This has only worked for a few specific configurations in the past, and now they are explicitly unsupported.

This means that for stretch all systems where /usr is a separate partition need to use an initramfs generator that will mount /usr. All initramfs generators in Stretch do so.

5.1.2. Noteworthy obsolete packages

The following is a list of known and noteworthy obsolete packages (see Section 4.8, “Obsolete packages” for a description).

The list of obsolete packages includes:

5.1.3. Deprecated components for Stretch

With the next release of Debian 10 (codenamed Buster) some features will be deprecated. Users will need to migrate to other alternatives to prevent trouble when updating to 10.

This includes the following features:

  • TODO: Add items if any

5.1.4. Things to do post upgrade before rebooting

When apt-get dist-upgrade has finished, the formal upgrade is complete, but there are some other things that should be taken care of before the next reboot.

      add list of items here
      
    

5.1.5. Executables are now compiled as position independent executables (PIE) by default

[Note]Note

This section mainly intended for developers or system administrators. Desktop users are unlikely to be affected by this section.

By default, the GNU GCC 6 compiler provided by Debian stretch will compile all executables as position independent. This provides a mitigation for an entire class of vulnerabilities, but it also leads to some changes that are worth being aware of.

  • The file tool (among other) will classify such binaries as "shared object" rather than an "executable". If you have filters based on binary files, these may need to be updated (e.g. spamfilters).

  • Static libraries being compiled into an executable now also need to be compiled as position independent code. The following error message from the linker is a symptom of this:

    relocation ... against '[SYMBOL]' can not be used when making a shared object; recompile with -fPIC
    

  • Historically, position independent executables have been associated with performance loss on some hardware. Notably the Debian architecture i386 (32-bit Intel machines). While GCC 5 and GCC 6 have greatly improved performance for position independent executables on 32-bit Intel, this optimisation may not be applicable to all architectures. Please consider evaluating the performance of your code if you are targetting machine architectures with very limited number of registers.

5.2. Limitations in security support

There are some packages where Debian cannot promise to provide minimal backports for security issues. These are covered in the following subsections.

Note that the package debian-security-support helps to track security support status of installed packages.

5.2.1. Security status of web browsers

Debian 9 includes several browser engines which are affected by a steady stream of security vulnerabilities. The high rate of vulnerabilities and partial lack of upstream support in the form of long term branches make it very difficult to support these browsers with backported security fixes. Additionally, library interdependencies make it impossible to update to newer upstream releases. Therefore, browsers built upon the webkit, qtwebkit and khtml engines are included in Stretch, but not covered by security support. These browsers should not be used against untrusted websites.

For general web browser use we recommend Firefox or Chromium.

Chromium - while built upon the Webkit codebase - is a leaf package, which will be kept up-to-date by rebuilding the current Chromium releases for stable. Firefox and Icedove will also be kept up-to-date by rebuilding the current ESR releases for stable.

5.2.2. Lack of security support for the ecosystem around libv8 and Node.js

The Node.js platform is built on top of libv8-3.14, which experiences a high volume of security issues, but there are currently no volunteers within the project or the security team sufficiently interested and willing to spend the large amount of time required to stem those incoming issues.

Unfortunately, this means that libv8-3.14, nodejs, and the associated node-* package ecosystem should not currently be used with untrusted content, such as unsanitized data from the Internet.

In addition, these packages will not receive any security updates during the lifetime of the Stretch release.

5.3. Package specific issues

In most cases, packages should upgrade smoothly between Jessie and Stretch. There are a small number of cases where some intervention may be required, either before or during the upgrade; these are detailed below on a per-package basis.

5.3.1. Older ciphers and SSH1 protocol disabled in OpenSSH by default

The OpenSSH 7 release has disabled some older ciphers and the SSH1 protocol by default. Please be careful when upgrading machines, where you only have SSH access.

Please refer to the OpenSSH documentation for more information.

5.3.2. Possible backwards incompatible changes to APT

This section covers some of the incompatible changes to APT that may affect your system.

5.3.2.1. APT now fetches files with an unprivileged user ("_apt")

APT will now attempt to discard all root privileges before fetching files from mirrors. APT can detect some common cases where this will fail and fallback to fetching things as root with a warning. However, it may fail to detect some exotic setups (e.g. uid-specific firewall rules).

If you experience issues with this feature, please change to the "_apt" user and check that it:

  • has read access to files in /var/lib/apt/lists and /var/cache/apt/archives.

  • has read access to the APT trust store (/etc/apt/trusted.gpg and /etc/apt/trusted.gpg.d/)

  • can resolve DNS names and download files. Example methods for testing:

    # From the dnsutils package (if using tor, please check with tor-resolve instead).
    $ nslookup debian.org >/dev/null || echo "Cannot resolve debian.org"
    $ wget -q https://debian.org/ -O- > /dev/null || echo "Cannot download index page of debian.org"
    

    For DNS issues, please check that /etc/resolv.conf is readable.

5.3.2.2. New requirements for APT repository

[Note]Note

This section only applies if you have (or intend to use) third-party repositories enabled or if you maintain an APT repository.

To improve the download stability and ensure security of the downloaded content, APT now requires the following from an APT repository:

  • The InRelease file must be available

  • All metadata must include at least SHA256 checksums of all items. This includes the gpg signature of the InRelease file.

  • Signatures on the InRelease file should be done with a key at the size of 2048 bit or larger.

If you rely on a third-party repository that cannot comply with the above, please urge them to upgrade their repository. More information about the InRelease file can be found on the Debian Wiki.

5.3.3. The Xorg server is no longer setuid root by default

[Note]Note

This change only applies if your X Display Manager supports running X as rootless (or if you start X manually via startx). Currently the only known display manager supporting this is gdm. Other display managers simply start X as root regardless of this change.

This reduces the risk of privilege escalation via bugs in the X server. However, it has some requirements for working:

  • It needs logind and libpam-systemd.

  • It needs a kernel video driver (as Xorg cannot talk directly to the hardware anymore).

  • It needs to run on the virtual console it was started from.

When run as a regular user, the Xorg log will be available from ~/.local/share/xorg/.

If these requirements are not possible, please install the xserver-xorg-legacy package to reinstate the setuid Xorg.

5.3.4. Upstart removed

Due to the lack of upstream maintainers, the Upstart init system has been removed from Stretch. If your system relies on this package, you should note that it will not be updated during the lifetime of Debian 9, and starting from Debian 10 (Buster), upstart jobs could be removed from packages.

Please consider switching to a supported init system, like systemd or openrc.

5.3.5. The debhelper tool now generates dbgsym packages by default

[Note]Note

This section mainly intended for developers or organizations that build their own debian packages.

The debhelper tool suite will now generate "dbgsym" packages by default for ELF binaries. If you develop and package binaries, please check that your tooling supports these extra auto-generated packages.

If you use reprepro, you want to upgrade it to at least version 4.17.0. At the time of writing, the aptly does not support dbgsym packages.

Should your tooling be unable to cope with these gracefully, you can ask debhelper to disable this feature by adding "noautodbgsym" in the DEB_BUILD_OPTIONS variable of your build service. Please see the dh_strip manpage for more information