This is not strictly needed for integrity (since we already include
the NAR hash in the fingerprint) but it helps against endless data
attacks [1]. (However, this will also require
download-from-binary-cache.pl to bail out if it receives more than the
specified number of bytes.)
[1] https://isis.poly.edu/~jcappos/papers/cappos_mirror_ccs_08.pdf
chroot only changes the process root directory, not the mount namespace root
directory, and it is well-known that any process with chroot capability can
break out of a chroot "jail". By using pivot_root as well, and unmounting the
original mount namespace root directory, breaking out becomes impossible.
Non-root processes typically have no ability to use chroot() anyway, but they
can gain that capability through the use of clone() or unshare(). For security
reasons, these syscalls are limited in functionality when used inside a normal
chroot environment. Using pivot_root() this way does allow those syscalls to be
put to their full use.
In some cases the bash builtin command "cd" can print the variable $CWD
to stdout. This caused the install script to fail while copying files
because the source path was wrong.
Fixes#476.
We only need to sign the store path, NAR hash and references (the
"fingerprint"). Everything else is irrelevant to security. For
instance, the compression algorithm or the hash of the compressed NAR
don't matter as long as the contents of the uncompressed NAR are
correct.
(Maybe we should include derivers in the fingerprint, but they're
broken and nobody cares about them. Also, it might be nice in the
future if .narinfos contained signatures from multiple independent
signers. But that's impossible if the deriver is included in the
fingerprint, since everybody will tend to have a different deriver for
the same store path.)
Also renamed the "Signature" field to "Sig" since the format changed
in an incompatible way.
Sodium's Ed25519 signatures are much shorter than OpenSSL's RSA
signatures. Public keys are also much shorter, so they're now
specified directly in the nix.conf option ‘binary-cache-public-keys’.
The new command ‘nix-store --generate-binary-cache-key’ generates and
prints a public and secret key.
It moves runHook to a later position in the rcfile. After that we are
able to set the PS1 environment-variable for a nix-shell environment
e.g.:
# turn the color of the prompt to blue
shellHook = ''
export PS1="\n\[\033[1;34m\][\u@\h:\w]$\[\033[0m\] ";
'';
