| Message ID | 1461339521-123191-4-git-send-email-seth.forshee@canonical.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
Quoting Seth Forshee (seth.forshee@canonical.com): > Both of these filesystems already have use cases for mounting the > same super block from multiple user namespaces. For sysfs this > happens when using criu for snapshotting a container, where sysfs > is mounted in the containers network ns but the hosts user ns. > The cgroup filesystem shares the same super block for all mounts > of the same hierarchy regardless of the namespace. > > As a result, the restriction on mounting a super block from a > single user namespace creates regressions for existing uses of > these filesystems. For these specific filesystems this > restriction isn't really necessary since the backing store is > objects in kernel memory and thus the ids assigned from inodes > is not subject to translation relative to s_user_ns. > > Add a new filesystem flag, FS_USERNS_SHARE_SB, which when set > causes sget_userns() to skip the check of s_user_ns. Set this > flag for the sysfs and cgroup filesystems to fix the > regressions. > > Signed-off-by: Seth Forshee <seth.forshee@canonical.com> Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com> thanks. > --- > fs/super.c | 3 ++- > fs/sysfs/mount.c | 3 ++- > include/linux/fs.h | 1 + > kernel/cgroup.c | 4 ++-- > 4 files changed, 7 insertions(+), 4 deletions(-) > > diff --git a/fs/super.c b/fs/super.c > index 092a7828442e..ead156b44bf8 100644 > --- a/fs/super.c > +++ b/fs/super.c > @@ -472,7 +472,8 @@ retry: > hlist_for_each_entry(old, &type->fs_supers, s_instances) { > if (!test(old, data)) > continue; > - if (user_ns != old->s_user_ns) { > + if (!(type->fs_flags & FS_USERNS_SHARE_SB) && > + user_ns != old->s_user_ns) { > spin_unlock(&sb_lock); > if (s) { > up_write(&s->s_umount); > diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c > index f3db82071cfb..9555accd4322 100644 > --- a/fs/sysfs/mount.c > +++ b/fs/sysfs/mount.c > @@ -59,7 +59,8 @@ static struct file_system_type sysfs_fs_type = { > .name = "sysfs", > .mount = sysfs_mount, > .kill_sb = sysfs_kill_sb, > - .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT, > + .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT | > + FS_USERNS_SHARE_SB, > }; > > int __init sysfs_init(void) > diff --git a/include/linux/fs.h b/include/linux/fs.h > index be0f8023e28c..66a639ec1bc4 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -1988,6 +1988,7 @@ struct file_system_type { > #define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */ > #define FS_USERNS_DEV_MOUNT 16 /* A userns mount does not imply MNT_NODEV */ > #define FS_USERNS_VISIBLE 32 /* FS must already be visible */ > +#define FS_USERNS_SHARE_SB 64 /* Allow sharing sb between userns-es */ > #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */ > struct dentry *(*mount) (struct file_system_type *, int, > const char *, void *); > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 671dc05c0b0f..9c9aa27e531a 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -2247,14 +2247,14 @@ static struct file_system_type cgroup_fs_type = { > .name = "cgroup", > .mount = cgroup_mount, > .kill_sb = cgroup_kill_sb, > - .fs_flags = FS_USERNS_MOUNT, > + .fs_flags = FS_USERNS_MOUNT | FS_USERNS_SHARE_SB, > }; > > static struct file_system_type cgroup2_fs_type = { > .name = "cgroup2", > .mount = cgroup_mount, > .kill_sb = cgroup_kill_sb, > - .fs_flags = FS_USERNS_MOUNT, > + .fs_flags = FS_USERNS_MOUNT | FS_USERNS_SHARE_SB, > }; > > static char *cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen, > -- > 1.9.1
diff --git a/fs/super.c b/fs/super.c index 092a7828442e..ead156b44bf8 100644 --- a/fs/super.c +++ b/fs/super.c @@ -472,7 +472,8 @@ retry: hlist_for_each_entry(old, &type->fs_supers, s_instances) { if (!test(old, data)) continue; - if (user_ns != old->s_user_ns) { + if (!(type->fs_flags & FS_USERNS_SHARE_SB) && + user_ns != old->s_user_ns) { spin_unlock(&sb_lock); if (s) { up_write(&s->s_umount); diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c index f3db82071cfb..9555accd4322 100644 --- a/fs/sysfs/mount.c +++ b/fs/sysfs/mount.c @@ -59,7 +59,8 @@ static struct file_system_type sysfs_fs_type = { .name = "sysfs", .mount = sysfs_mount, .kill_sb = sysfs_kill_sb, - .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT, + .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT | + FS_USERNS_SHARE_SB, }; int __init sysfs_init(void) diff --git a/include/linux/fs.h b/include/linux/fs.h index be0f8023e28c..66a639ec1bc4 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1988,6 +1988,7 @@ struct file_system_type { #define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */ #define FS_USERNS_DEV_MOUNT 16 /* A userns mount does not imply MNT_NODEV */ #define FS_USERNS_VISIBLE 32 /* FS must already be visible */ +#define FS_USERNS_SHARE_SB 64 /* Allow sharing sb between userns-es */ #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */ struct dentry *(*mount) (struct file_system_type *, int, const char *, void *); diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 671dc05c0b0f..9c9aa27e531a 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2247,14 +2247,14 @@ static struct file_system_type cgroup_fs_type = { .name = "cgroup", .mount = cgroup_mount, .kill_sb = cgroup_kill_sb, - .fs_flags = FS_USERNS_MOUNT, + .fs_flags = FS_USERNS_MOUNT | FS_USERNS_SHARE_SB, }; static struct file_system_type cgroup2_fs_type = { .name = "cgroup2", .mount = cgroup_mount, .kill_sb = cgroup_kill_sb, - .fs_flags = FS_USERNS_MOUNT, + .fs_flags = FS_USERNS_MOUNT | FS_USERNS_SHARE_SB, }; static char *cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
Both of these filesystems already have use cases for mounting the same super block from multiple user namespaces. For sysfs this happens when using criu for snapshotting a container, where sysfs is mounted in the containers network ns but the hosts user ns. The cgroup filesystem shares the same super block for all mounts of the same hierarchy regardless of the namespace. As a result, the restriction on mounting a super block from a single user namespace creates regressions for existing uses of these filesystems. For these specific filesystems this restriction isn't really necessary since the backing store is objects in kernel memory and thus the ids assigned from inodes is not subject to translation relative to s_user_ns. Add a new filesystem flag, FS_USERNS_SHARE_SB, which when set causes sget_userns() to skip the check of s_user_ns. Set this flag for the sysfs and cgroup filesystems to fix the regressions. Signed-off-by: Seth Forshee <seth.forshee@canonical.com> --- fs/super.c | 3 ++- fs/sysfs/mount.c | 3 ++- include/linux/fs.h | 1 + kernel/cgroup.c | 4 ++-- 4 files changed, 7 insertions(+), 4 deletions(-)