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    Subject[PATCH 4.1 08/65] mnt: Refactor the logic for mounting sysfs and proc in a user namespace
    Date
    4.1-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: "Eric W. Biederman" <ebiederm@xmission.com>

    commit 1b852bceb0d111e510d1a15826ecc4a19358d512 upstream.

    Fresh mounts of proc and sysfs are a very special case that works very
    much like a bind mount. Unfortunately the current structure can not
    preserve the MNT_LOCK... mount flags. Therefore refactor the logic
    into a form that can be modified to preserve those lock bits.

    Add a new filesystem flag FS_USERNS_VISIBLE that requires some mount
    of the filesystem be fully visible in the current mount namespace,
    before the filesystem may be mounted.

    Move the logic for calling fs_fully_visible from proc and sysfs into
    fs/namespace.c where it has greater access to mount namespace state.

    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/namespace.c | 8 +++++++-
    fs/proc/root.c | 5 +----
    fs/sysfs/mount.c | 5 +----
    include/linux/fs.h | 2 +-
    4 files changed, 10 insertions(+), 10 deletions(-)

    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -2332,6 +2332,8 @@ unlock:
    return err;
    }

    +static bool fs_fully_visible(struct file_system_type *fs_type);
    +
    /*
    * create a new mount for userspace and request it to be added into the
    * namespace's tree
    @@ -2363,6 +2365,10 @@ static int do_new_mount(struct path *pat
    flags |= MS_NODEV;
    mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
    }
    + if (type->fs_flags & FS_USERNS_VISIBLE) {
    + if (!fs_fully_visible(type))
    + return -EPERM;
    + }
    }

    mnt = vfs_kern_mount(type, flags, name, data);
    @@ -3164,7 +3170,7 @@ bool current_chrooted(void)
    return chrooted;
    }

    -bool fs_fully_visible(struct file_system_type *type)
    +static bool fs_fully_visible(struct file_system_type *type)
    {
    struct mnt_namespace *ns = current->nsproxy->mnt_ns;
    struct mount *mnt;
    --- a/fs/proc/root.c
    +++ b/fs/proc/root.c
    @@ -112,9 +112,6 @@ static struct dentry *proc_mount(struct
    ns = task_active_pid_ns(current);
    options = data;

    - if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
    - return ERR_PTR(-EPERM);
    -
    /* Does the mounter have privilege over the pid namespace? */
    if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
    return ERR_PTR(-EPERM);
    @@ -159,7 +156,7 @@ static struct file_system_type proc_fs_t
    .name = "proc",
    .mount = proc_mount,
    .kill_sb = proc_kill_sb,
    - .fs_flags = FS_USERNS_MOUNT,
    + .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
    };

    void __init proc_root_init(void)
    --- a/fs/sysfs/mount.c
    +++ b/fs/sysfs/mount.c
    @@ -31,9 +31,6 @@ static struct dentry *sysfs_mount(struct
    bool new_sb;

    if (!(flags & MS_KERNMOUNT)) {
    - if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
    - return ERR_PTR(-EPERM);
    -
    if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
    return ERR_PTR(-EPERM);
    }
    @@ -58,7 +55,7 @@ static struct file_system_type sysfs_fs_
    .name = "sysfs",
    .mount = sysfs_mount,
    .kill_sb = sysfs_kill_sb,
    - .fs_flags = FS_USERNS_MOUNT,
    + .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
    };

    int __init sysfs_init(void)
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -1897,6 +1897,7 @@ struct file_system_type {
    #define FS_HAS_SUBTYPE 4
    #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_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
    struct dentry *(*mount) (struct file_system_type *, int,
    const char *, void *);
    @@ -1984,7 +1985,6 @@ extern int vfs_ustat(dev_t, struct kstat
    extern int freeze_super(struct super_block *super);
    extern int thaw_super(struct super_block *super);
    extern bool our_mnt(struct vfsmount *mnt);
    -extern bool fs_fully_visible(struct file_system_type *);

    extern int current_umask(void);




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