Re: [libvirt] [PATCH] LXC: create a bind mount for sysfs when enable userns but disable netns

>> @@ -826,8 +829,25 @@ static int lxcContainerMountBasicFS(bool userns_enabled) >> bool bindOverReadonly; >> virLXCBasicMountInfo const *mnt = &lxcBasicMounts[i]; >> >> + /* When enable userns but disable netns, kernel will >> + * forbid us doing a new fresh mount for sysfs. >> + * So we had to do a bind mount for sysfs instead. >> + */ >> + if (userns_enabled && netns_disabled && >> + STREQ(mnt->src, "sysfs")) { >> + if (VIR_STRDUP(mnt_src, "/sys") < 0) { >> + goto cleanup; >> + } > > This is clearly broken and looks very untested to me. > It's broken now. But when I submitted this patch last year, it's not.

> It will issue this mount call: > mount("/sys", "/sys", "sysfs", MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_BIND, NULL) > because the code runs after pivot_root(2). > i.e, /sys will be still empty after that and no sysfs at all there. > As libvirt will later remount /sys readonly creating a container will > fail with the most useless error message: > Error: internal error: guest failed to start: Unable to create > directory /sys/fs/: Read-only file system > or > Error: internal error: guest failed to start: Unable to create > directory /sys/fs/cgroup: Read-only file system > > Please note that changing "/sys" to "/.oldroot/sys" will not solve the > issue as this code runs already in the new > namespace and therefore the old mount tree is locked, thus MS_BIND is > not allowed. > > This brings me to the question, why do you handle the netns_disabled > case anyway? Please check the discussion at: http://lists.linux-foundation.org/pipermail/containers/2014-July/034721.html > If in the XML file no network is specified just create a new and empty > network namespace. > Bindmounting /sys into the container is a security issue. This is why > mounting sysfs without a netns > was disabled to begin with. Yes, I tried to propose enable netns by default, but Dan thought that we should allow containers sharing the host's network: http://www.redhat.com/archives/libvir-list/2013-August/msg01025.html So we should allow user create containers without netns, they should know what they do if they read libvirt's docs See docs patch describe security considerations: http://www.redhat.com/archives/libvir-list/2013-September/msg00562.html