"chenhanxiao@xxxxxxxxxxxxxx" <chenhanxiao@xxxxxxxxxxxxxx> writes: >> -----Original Message----- >> From: Eric W. Biederman [mailto:ebiederm@xxxxxxxxxxxx] >> Sent: Saturday, July 12, 2014 12:29 AM >> To: Serge E. Hallyn >> Cc: Chen, Hanxiao/陈 晗霄; Serge Hallyn (serge.hallyn@xxxxxxxxxx); Greg >> Kroah-Hartman; containers@xxxxxxxxxxxxxxxxxxxxxxxxxx; >> linux-kernel@xxxxxxxxxxxxxxx >> Subject: Re: Could not mount sysfs when enable userns but disable netns >> >> "Serge E. Hallyn" <serge@xxxxxxxxxx> writes: >> >> > Quoting chenhanxiao@xxxxxxxxxxxxxx (chenhanxiao@xxxxxxxxxxxxxx): >> >> Hello, >> >> >> >> How to reproduce: >> >> 1. Prepare a container, enable userns and disable netns >> >> 2. use libvirt-lxc to start a container >> >> 3. libvirt could not mount sysfs then failed to start. >> >> >> >> Then I found that >> >> commit 7dc5dbc879bd0779924b5132a48b731a0bc04a1e says: >> >> "Don't allow mounting sysfs unless the caller has CAP_SYS_ADMIN rights >> >> over the net namespace." >> >> >> >> But why should we check sysfs mouont permission over net namespace? >> >> We've already checked CAP_SYS_ADMIN though. >> >> We already checked capable(CAP_SYS_ADMIN) and it failed. > > But on my machine, capable(CAP_SYS_ADMIN) passed > but failed in kobj_ns_current_may_mount. No. capable(CAP_SYS_ADMIN) did not pass. fs_fully_visible did passed. There is a significant distinction. If capable(CAP_SYS_ADMIN) had passed kobj_ns_current_may_mount (which is a fancy way of saying ns_capable(net->user_ns, CAP_SYS_ADMIN)) would also have passed. > I added some printks in sysfs_mount: > if (!(flags & MS_KERNMOUNT)) { > - if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type)) > + if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type)) { > + printk(KERN_WARNING "Failed in capable\n"); > return ERR_PTR(-EPERM); > + } > > - if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET)) > + if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET)) { > + printk(KERN_WARNING "Failed in kobj_ns_current_may_mount\n"); > return ERR_PTR(-EPERM); > + } > > And found: > Jul 14 09:55:26 localhost systemd: Starting Container lxc-chx. > Jul 14 09:55:26 localhost systemd-machined: New machine lxc-chx. > Jul 14 09:55:26 localhost systemd: Started Container lxc-chx. > Jul 14 09:55:26 localhost kernel: [ 784.044709] Failed in kobj_ns_current_may_mount > Jul 14 09:55:26 localhost systemd-machined: Machine lxc-chx terminated. > >> >> >> What the relationship between sysfs and net namespace, >> >> or this check is a little redundant? >> >> You want a bind mount not a new fresh mount. >> > > Yes, we need to modify libvirt's codes to deal with sysfs > when enable userns but disable netns. Please go for it. I don't have any insignt into libvirt so I can't help you there. Eric _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
