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. 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
