Limiting access to abstract unix domain sockets
I'm working on using container technology to sandbox desktop applications, and I've run into an issue with abstract unix domain sockets. Generally unix domain sockets work fine in a container situation because they are naturally namespaced via the filesystem namespace.
However, abstract socket addresses are global to the *network* namespace. This means that if you need to share the host network namespace (typically so you have full ip networking access) you can't limit access to *any* service that listens to an abstract unix socket.
I don't particularly need to use abstract sockets, so it would be ok to just disallow its use in the container. I've looked at using seccomp for this, but it doesn't seem to help here, as it needs to dereference the socket address to tell if its abstract or not.
Does anyone have any idea how to do this?
A message that is not in the archive (sent off-list or not yet received): [email protected]
Quoted 11 lines · Alexander Larsson
I'm working on using container technology to sandbox desktop applications, and I've run into an issue with abstract unix domain sockets. Generally unix domain sockets work fine in a container situation because they are naturally namespaced via the filesystem namespace.
However, abstract socket addresses are global to the *network* namespace. This means that if you need to share the host network namespace (typically so you have full ip networking access) you can't limit access to *any* service that listens to an abstract unix socket.
Quoted 6 lines
I don't particularly need to use abstract sockets, so it would be ok to just disallow its use in the container. I've looked at using seccomp for this, but it doesn't seem to help here, as it needs to dereference the socket address to tell if its abstract or not.
Does anyone have any idea how to do this?
You should be able to use recent apparmor or selinux.
Quoted 12 lines · Serge Hallyn
Quoted 11 lines · Alexander Larsson
I'm working on using container technology to sandbox desktop applications, and I've run into an issue with abstract unix domain sockets. Generally unix domain sockets work fine in a container situation because they are naturally namespaced via the filesystem namespace.
However, abstract socket addresses are global to the *network* namespace. This means that if you need to share the host network namespace (typically so you have full ip networking access) you can't limit access to *any* service that listens to an abstract unix socket.
Quoted 8 lines
Quoted 6 lines
I don't particularly need to use abstract sockets, so it would be ok to just disallow its use in the container. I've looked at using seccomp for this, but it doesn't seem to help here, as it needs to dereference the socket address to tell if its abstract or not.
Does anyone have any idea how to do this?
You should be able to use recent apparmor or selinux.
Agreed. If you are trying to firewall an application the lsm's are the firewall mechanism we have.
If you are building an application from scratch I would tend to recommend the use of privilege separation, and only allowing the ``privileged'' part of your application to setup network sockets.
To me one of the scaries things an application can have is a network socket to the outside world.
Eric
A message that is not in the archive (sent off-list or not yet received): [email protected]
Quoted 26 lines · Eric W. Biederman
Quoted 12 lines · Serge Hallyn
Quoted 11 lines · Alexander Larsson
I'm working on using container technology to sandbox desktop applications, and I've run into an issue with abstract unix domain sockets. Generally unix domain sockets work fine in a container situation because they are naturally namespaced via the filesystem namespace.
However, abstract socket addresses are global to the *network* namespace. This means that if you need to share the host network namespace (typically so you have full ip networking access) you can't limit access to *any* service that listens to an abstract unix socket.
Quoted 8 lines
Quoted 6 lines
I don't particularly need to use abstract sockets, so it would be ok to just disallow its use in the container. I've looked at using seccomp for this, but it doesn't seem to help here, as it needs to dereference the socket address to tell if its abstract or not.
Does anyone have any idea how to do this?
You should be able to use recent apparmor or selinux.
Agreed. If you are trying to firewall an application the lsm's are the firewall mechanism we have.
Quoted 6 lines
If you are building an application from scratch I would tend to recommend the use of privilege separation, and only allowing the ``privileged'' part of your application to setup network sockets.
To me one of the scaries things an application can have is a network socket to the outside world.
Well, a great many apps don't need network access. Like say a game. For these there would not be a problem, just give them their own network namespace.
But, if we're talking about an existing (not privilege separated) complex networking app, say an email client. How would you recommend that such an app be contained (network-wise) in a generic framework? We could give it its own network and IP that we NAT. But is this really more "secure" in any sense? The app can still send stuff on the outside network. I guess the inability to handle inbound traffic helps, but is this all?
A message that is not in the archive (sent off-list or not yet received): [email protected]
Quoted 38 lines · Alexander Larsson
Quoted 26 lines · Eric W. Biederman
Quoted 12 lines · Serge Hallyn
Quoted 11 lines · Alexander Larsson
I'm working on using container technology to sandbox desktop applications, and I've run into an issue with abstract unix domain sockets. Generally unix domain sockets work fine in a container situation because they are naturally namespaced via the filesystem namespace.
However, abstract socket addresses are global to the *network* namespace. This means that if you need to share the host network namespace (typically so you have full ip networking access) you can't limit access to *any* service that listens to an abstract unix socket.
Quoted 8 lines
Quoted 6 lines
I don't particularly need to use abstract sockets, so it would be ok to just disallow its use in the container. I've looked at using seccomp for this, but it doesn't seem to help here, as it needs to dereference the socket address to tell if its abstract or not.
Does anyone have any idea how to do this?
You should be able to use recent apparmor or selinux.
Agreed. If you are trying to firewall an application the lsm's are the firewall mechanism we have.
Quoted 6 lines
If you are building an application from scratch I would tend to recommend the use of privilege separation, and only allowing the ``privileged'' part of your application to setup network sockets.
To me one of the scaries things an application can have is a network socket to the outside world.
Well, a great many apps don't need network access. Like say a game. For these there would not be a problem, just give them their own network namespace.
Quoted 7 lines
But, if we're talking about an existing (not privilege separated) complex networking app, say an email client. How would you recommend that such an app be contained (network-wise) in a generic framework? We could give it its own network and IP that we NAT. But is this really more "secure" in any sense? The app can still send stuff on the outside network. I guess the inability to handle inbound traffic helps, but is this all?
I suspect there won't be an answer here because your question has gone off the original topic and become too unspecific.
Basically you were right originally: so long as you share the host's network namespace, you can use its abstract sockets. LSMs are one way to actually clamp down on that. For instance, on new enough apparmor, by default applications under different apparmor profiles should not be able to connect to each other's sockets (configurable in policy).
-serge