On 6/10/23 08:27, Ian Kent wrote:
On 5/10/23 23:47, Miklos Szeredi wrote:
On Thu, 5 Oct 2023 at 06:23, Ian Kent <raven@xxxxxxxxxx> wrote:
The proc interfaces essentially use <mount namespace>->list to provide
the mounts that can be seen so it's filtered by mount namespace of the
task that's doing the open().
See fs/namespace.c:mnt_list_next() and just below the m_start(),
m_next(),
/proc/$PID/mountinfo will list the mount namespace of $PID. Whether
current task has permission to do so is decided at open time.
listmount() will list the children of the given mount ID. The mount
ID is looked up in the task's mount namespace, so this cannot be used
to list mounts of other namespaces. It's a more limited interface.
Yep. But isn't the ability to see these based on task privilege?
Is the proc style restriction actually what we need here (or some
variation
of that implementation)?
An privileged task typically has the init namespace as its mount
namespace
and mounts should propagate from there so it should be able to see all
mounts.
If the file handle has been opened in a task that is using some other
mount
namespace then presumably that's what the program author wants the
task to see.
So I'm not sure I see a problem obeying the namespace of a given task.
I've had a look through the code we had in the old fsinfo() proposal
because I think we need to consider the use cases that are needed.
IIRC initially we had a flag FSINFO_ATTR_MOUNT_CHILDREN that essentially
enumerated the children of the given mount in much the same way as is
done now in this system call.
But because we needed to enumerate mounts in the same way as the proc file
system mount tables a flag FSINFO_ATTR_MOUNT_ALL was added that essentially
used the mount namespace mounts list in a similar way to the proc file
system so that a list of mounts for a mount namespace could be retrieved.
This later use case is what is used by processes that monitor mounts and
is what's needed more so than enumerating the children as we do now.
I'm still looking at the mount id lookup.
Ian
Ian
I sort of understand the reasoning behind calling into a security hook
on entry to statmount() and listmount(). And BTW I also think that if
statmount() and listmount() is limited in this way, then the same
limitation should be applied to the proc interfaces. But that needs
to be done real carefully because it might cause regressions. OTOH if
it's only done on the new interfaces, then what is the point, since
the old interfaces will be available indefinitely?
Also I cannot see the point in hiding some mount ID's from the list.
It seems to me that the list is just an array of numbers that in
itself doesn't carry any information.
Thanks,
Miklos
