Monday, 15 October 2012

HOWTO: sudo + cowbuilder (+git-buildpackage)

In case you tried to use git-buildpackage and wanted to use cowbuilder as a builder, you might have ran into the error

sudo: sorry, you are not allowed to preserve the environment

This is due to a change in sudo default configuration in version 1.7.4p4-2 (I know, is true since 2010) which doesn't allow the execution of commands via sudo using the parameter '-E' which means 'setenv'.

The news item even explicitly states pbuilder can be affected by this because it wants to port over to the pbuilder environment the HOME environment variable and suggests using

Defaults env_keep += HOME

But adding such a line to your /etc/sudoers.d/01_pbuilders file (/etc/sudoers is recommended to be touched only by the package) will do the  same for all commands and users ran via sudo, which is, according to my preferences, too permissive.

The irony is that running git-buildpackage --git-pbuilder  will invoke sudo -E cowbuilder so the env_keep suggested fix will not work because for -E to be allowed, setenv needs to be set in sudoers. This would defeat the purpose of env_reset, if done for all commands, but we can do a better job if we allow this kind of change only for the cowbuilder and pbuilder commands. You do have different commands that are allowed explicitly stated, don't you?

On my system I have made a group especially for people allowed to do packaging work, the group is called 'pack'. The only account in that group is my own.

Also, I have defined a command alias named PBUILDERS which looks something like this:

Cmnd_Alias PBUILDERS = /usr/sbin/pbuilder, /usr/sbin/cowbuilder

Running PBUILDERS is already restricted to the pack group. Here is an example that requires password on run:


So all that needs to be done is to allow setenv for the PBUILDERS commands. Reading through the sudoers manpage and after some trial and error (use visudo for editting sudoers files - visudo -f /etc/sudoers.d/01_pbuilders) I found out that the symbols that distinguish between commands, users and groups in a 'Defaults' line needs to be right next to the 'Defaults' word. For command the sign is an exclamation sign '!' (for user lists it's ':') so since we want to link the exception to the command, not the user list, we'll use 'Defaults!':

Defaults! PBUILDERS setenv

Assuming you also have a PBUILDERS commands alias, this is what you need to be able to use git-buildpackage in conjunction with cowbuilder and sudo.

If there is a non-intrusive way to prevent sudo to use -E when invoking cowbuilder, please add your comment, I would be interested to know it.

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