We can just check the GPG signature for the upstream tarballs that are
GPG signed. We keep a copy of the relevant GPG keys in tree so that
we only use a controlled set of keys.
I validated the GPG keys by:
- Creating a fresh keyring.
- Importing the keys with gpg --receive-key.
- Importing my own GPG public key in that keyring.
- Importing the gpg keys that the PGP pathfinder told me were on the path
to those keys (which weren't directly in their keyring, so I had to
manually find some steps first).
- Using `gpg --check-sigs` to validate that the all those keys I got are
the right ones.
Then the relevant GPG keys were exported with `gpg --export --armor` and
stripped with https://github.com/glandium/pgpstrip/.
For MPC, the first GPG-signed version upstream was 0.8.2, while the GCC
script to download prerequisites downloads 0.8.1. So instead of using
0.8.1, we use 0.8.2, which we can verify.
For GMP, the GCC script downloads 4.3.2. The only web-of-trust path is
through a revoked key, which signs a revoked uid of the GMP key.
Releases newer than 5.1.0 are signed with a new key that can be
validated with the steps above. So instead of using 4.3.2, we use 5.1.3
(last of the 5.1.x line).
But MPFR 2.4.2, which the GCC script downloads, doesn't build against
GMP 5.1.3, so instead of that, we use MPFR 3.1.5.
Sadly, the remaining GCC prerequisites are not signed, so I had to:
- Download the files from ftp.gnu.org.
- Download the corresponding files from snapshot.debian.org.
- Compare the raw files when possible, or the uncompressed (not extracted)
files (when, thankfully, they matched).
- Validate those snapshot.debian.org files checksums against the
checksums in the corresponding Sources.bz2/xz files.
- Validate the Sources.bz2/xz checksums against the corresponding InRelease
files.
- Validate the InRelease files GPG signatures against the Debian
archives keyring.
With all those things we actually don't get through the GCC script, we
also change how we get those prerequisites, by diverting the commands
the script runs and making it output the urls instead of downloading and
extracting the files.
All downloaded files, GPG-validated or otherwise, have their SHA-256
digest checked against a list in build/unix/build-gcc/checksums.
--HG--
extra : rebase_source : e6809a6ac392e6c5f99801826e1d30bdeee7ddf5
Mike Hommey