get_args() exception handling before this fix only dealt with
subclasses of "Error", but we have to expect other exceptions
there, too.
In any case, if we have some fatal exception here, we must
terminate with rc 2.
ArgumentTypeError: emit a short error message - usually this is
a user error, invoking borg in a wrong way.
Other exceptions: full info and traceback.
for the other compression methods, this is done in
the base class, but the zlib legacy does not call
that method as it also removes the header bytes,
which zlib legacy does not have.
Hint for Cygwin users to make sure they use a virtual environment.
Not using a virtual environment will be likely troublesome if there is already a Python installed on Windows.
also: do a small optimisation in borg check:
if the type of the repo object is not ROBJ_ARCHIVE_META, we
can skip the object, it can not contain valid archive meta data.
if the type is correct, this is already a sufficient check, so
we can be quite sure that there will be valid archive metadata
in the object.
writing: put type into repoobj metadata
reading: check wanted type against type we got
repoobj metadata is encrypted and authenticated.
repoobj data is encrypted and authenticated, also (separately).
encryption and decryption of both metadata and data get the
same "chunk ID" as AAD, so both are "bound" to that (same) ID.
a repo-side attacker can neither see cleartext metadata/data,
nor successfully tamper with it (AEAD decryption would fail).
also, a repo-side attacker could not replace a repoobj A with a
differently typed repoobj B without borg noticing:
- the metadata/data is cryptographically bound to its ID.
authentication/decryption would fail on mismatch.
- the type check would fail.
thus, the problem (see CVEs in changelog) solved in borg 1 by the
manifest and archive TAMs is now already solved by the type check.
For many use cases, the repo-wide "rcompress" is more efficient.
Also, recreate --recompress calls add_chunk with overwrite=True,
which is unsupported with the AdHocCache.
