fscrypt.git/cli-tests/t_single_user.out, branch chr-fork-doc-02 Go tool for managing Linux filesystem encryption Strictly validate metadata file ownership by default 2022-02-23T20:35:04+00:00 Eric Biggers ebiggers@google.com 2022-02-23T20:35:04+00:00 74e870b7bd1585b4b509da47e0e75db66336e576 The metadata validation checks introduced by the previous commits are good, but to reduce the attack surface it would be much better to avoid reading and parsing files owned by other users in the first place. There are some possible use cases for users sharing fscrypt metadata files, but I think that for the vast majority of users it is unneeded and just opens up attack surface. Thus, make fscrypt (and pam_fscrypt) not process policies or protectors owned by other users by default. Specifically, * If fscrypt or pam_fscrypt is running as a non-root user, only policies and protectors owned by the user or by root can be used. * If fscrypt is running as root, any policy or protector can be used. (This is to match user expectations -- starting a sudo session should gain rights, not remove rights.) * If pam_fscrypt is running as root, only policies and protectors owned by root can be used. Note that this only applies when the root user themselves has an fscrypt login protector, which is rare. Add an option 'allow_cross_user_metadata' to /etc/fscrypt.conf which allows restoring the old behavior for anyone who really needs it. 
The metadata validation checks introduced by the previous commits are
good, but to reduce the attack surface it would be much better to avoid
reading and parsing files owned by other users in the first place.

There are some possible use cases for users sharing fscrypt metadata
files, but I think that for the vast majority of users it is unneeded
and just opens up attack surface.  Thus, make fscrypt (and pam_fscrypt)
not process policies or protectors owned by other users by default.
Specifically,

   * If fscrypt or pam_fscrypt is running as a non-root user, only
     policies and protectors owned by the user or by root can be used.

   * If fscrypt is running as root, any policy or protector can be used.
     (This is to match user expectations -- starting a sudo session
     should gain rights, not remove rights.)

   * If pam_fscrypt is running as root, only policies and protectors
     owned by root can be used.  Note that this only applies when the
     root user themselves has an fscrypt login protector, which is rare.

Add an option 'allow_cross_user_metadata' to /etc/fscrypt.conf which
allows restoring the old behavior for anyone who really needs it.
Make 'fscrypt setup' offer a choice of directory modes 2022-02-23T20:35:04+00:00 Eric Biggers ebiggers@google.com 2022-02-23T20:35:04+00:00 6e355131670ad014e45f879475ddf800f0080d41 World-writable directories are not appropriate for some systems, so offer a choice of single-user-writable and world-writable modes, with single-user-writable being the default. Add a new documentation section to help users decide which one to use. 
World-writable directories are not appropriate for some systems, so
offer a choice of single-user-writable and world-writable modes, with
single-user-writable being the default.  Add a new documentation section
to help users decide which one to use.