On 12/13/25 20:39, Alyssa Ross wrote: > Demi Marie Obenour writes: > >> On 12/13/25 16:42, Alyssa Ross wrote: >>> Demi Marie Obenour writes: >>> >>>> On 12/13/25 14:12, Alyssa Ross wrote: >>>>> Demi Marie Obenour writes: >>>>> >>>>>> It is quite possible that these Landlock rules are unnecessarily >>>>>> permissive, but all of the paths to which read and execute access is >>>>>> granted are part of the root filesystem and therefore assumed to be >>>>>> public knowledge. Removing access from any of them would only increase >>>>>> the risk of accidental breakage in the future, and would not provide any >>>>>> security improvements. seccomp *could* provide some improvements, but >>>>>> the effort needed is too high for now. >>>>>> >>>>>> Signed-off-by: Demi Marie Obenour >>>>>> --- >>>>>> .../template/data/service/xdg-desktop-portal-spectrum-host/run | 8 ++++++++ >>>>>> 1 file changed, 8 insertions(+) >>>>> >>>>> Are you sure this is working as intended? There's no rule allowing >>>>> access to Cloud Hypervisor's VSOCK socket, and yet it still seems to be >>>>> able to access that. Don't you need to set a rule that *restricts* >>>>> filesystem access and then add holes? Did you ever see this deny >>>>> anything? >>>> >>>> 'man 1 setpriv' states that '--landlock-access fs' blocks all >>>> filesystem access unless a subsequent --landlock-rule permits it. >>>> I tried running with no --landlock-rule flags and the execve of >>>> xdg-desktop-portal-spectrum-host failed as expected. >>>> >>>> The socket is passed over stdin, and I'm pretty sure Landlock >>>> doesn't restrict using an already-open file descriptor. >>>> xdg-desktop-portal-spectrum-host does need to find the path to the >>>> socket, but I don't think it ever accesses that path. >>> >>> I've been looking into this a bit myself, and from what I can tell >>> Landlock just doesn't restrict connecting to sockets at all, even if >>> they're inside directories that would otherwise be inaccessible. It's >>> able to connect to both Cloud Hypervisor's VSOCK socket and the D-Bus >>> socket even with a maximally restrictive landlock rule. So you were >>> right after all, sorry! >> >> That's not good at all! It's a trivial sandbox escape in so many cases. >> For instance, with access to D-Bus I can just call `systemd-run`. >> >> I'm CCing the Landlock and LSM mailing lists because if you are >> correct, then this is a bad security hole. > > I don't find it that surprising given the way landlock works. "connect" > (to a non-abstract AF_UNIX socket) is not an operation there's a > landlock action for, and it's not like the other actions care about > access to parent directories and the like — I was able to execute a > program via a symlink after only giving access to the symlink's target, > without any access to the directory containing the symlink or the > symlink itself, for example. Landlock, as I understand it, is intended > to block a specified set of operations (on particular file hierarchies), > rather than to completely prevent access to those hierarchies like > permissions or mount namespaces could, so the lack of a way to block > connecting to a socket is more of a missing feature than a security > hole. 'man 7 unix' states: On Linux, connecting to a stream socket object requires write permission on that socket; sending a datagram to a datagram socket likewise requires write permission on that socket. Landlock is definitely being inconsistent with DAC here. Also, this allows real-world sandbox breakouts. On systemd systems, the simplest way to escape is to use systemd-run to execute arbitrary commands. -- Sincerely, Demi Marie Obenour (she/her/hers)