This beefs up the READ_FULL_FILE_CONNECT_SOCKET logic of
read_full_file_full() a bit: when used a sender socket name may be
specified. If specified as NULL behaviour is as before: the client
socket name is picked by the kernel. But if specified as non-NULL the
client can pick a socket name to use when connecting. This is useful to
communicate a minimal amount of metainformation from client to server,
outside of the transport payload.
Specifically, these beefs up the service credential logic to pass an
abstract AF_UNIX socket name as client socket name when connecting via
READ_FULL_FILE_CONNECT_SOCKET, that includes the requesting unit name
and the eventual credential name. This allows servers implementing the
trivial credential socket logic to distinguish clients: via a simple
getpeername() it can be determined which unit is requesting a
credential, and which credential specifically.
Example: with this patch in place, in a unit file "waldo.service" a
configuration line like the following:
LoadCredential=foo:/run/quux/creds.sock
will result in a connection to the AF_UNIX socket /run/quux/creds.sock,
originating from an abstract namespace AF_UNIX socket:
@$RANDOM/unit/waldo.service/foo
(The $RANDOM is replaced by some randomized string. This is included in
the socket name order to avoid namespace squatting issues: the abstract
socket namespace is open to unprivileged users after all, and care needs
to be taken not to use guessable names)
The services listening on the /run/quux/creds.sock socket may thus
easily retrieve the name of the unit the credential is requested for
plus the credential name, via a simpler getpeername(), discarding the
random preifx and the /unit/ string.
This logic uses "/" as separator between the fields, since both unit
names and credential names appear in the file system, and thus are
designed to use "/" as outer separators. Given that it's a good safe
choice to use as separators here, too avoid any conflicts.
This is a minimal patch only: the new logic is used only for the unit
file credential logic. For other places where we use
READ_FULL_FILE_CONNECT_SOCKET it is probably a good idea to use this
scheme too, but this should be done carefully in later patches, since
the socket names become API that way, and we should determine the right
amount of info to pass over.
Let's use the new flag wherever we read key material/passphrases/hashes
off disk, so that people can plug in their own IPC service as backend if
they like, easily.
(My main goal was actually to support this for crypttab key files — i.e.
that you can specify AF_UNIX sockets as third column in crypttab — but
that's harder to implement, since the keys are read via libcryptsetup's
API, not ours.)
With gcc-9.0.1-0.10.fc30.x86_64:
../src/network/netdev/macsec.c: In function ‘config_parse_macsec_port’:
../src/network/netdev/macsec.c:584:24: warning: taking address of packed member of ‘struct <anonymous>’ may result in an unaligned pointer value [-Waddress-of-packed-member]
584 | dest = &c->sci.port;
| ^~~~~~~~~~~~
../src/network/netdev/macsec.c:592:24: warning: taking address of packed member of ‘struct <anonymous>’ may result in an unaligned pointer value [-Waddress-of-packed-member]
592 | dest = &b->sci.port;
| ^~~~~~~~~~~~
(The alignment was probably OK, but it's nicer to avoid the warning anyway.)
Media Access Control Security (MACsec) is an 802.1AE IEEE
industry-standard security technology that provides secure
communication for all traffic on Ethernet links.
MACsec provides point-to-point security on Ethernet links between
directly connected nodes and is capable of identifying and preventing
most security threats, including denial of service, intrusion,
man-in-the-middle, masquerading, passive wiretapping, and playback attacks.
Closes#5754
