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    Subject[PATCH -mm 6/8] user ns: implement shared mounts
    From: Serge E. Hallyn <serue@us.ibm.com>
    Subject: [PATCH -mm 6/8] user ns: implement shared mounts

    Implement shared-ns mounts, which allow containers in different user
    namespaces to share mounts. Without this, containers can obviously
    never even be started.

    Here is a sample smount.c (based on Miklos' version) which only
    does a bind mount of arg1 onto arg2, but making the destination
    a shared-ns mount.

    int main(int argc, char *argv[])
    {
    int type;
    if(argc != 3) {
    fprintf(stderr, "usage: %s src dest", argv[0]);
    return 1;
    }

    fprintf(stdout, "%s %s %s\n", argv[0], argv[1], argv[2]);

    type = MS_SHARE_NS | MS_BIND;
    setfsuid(getuid());

    if(mount(argv[1], argv[2], "none", type, "") == -1) {
    perror("mount");
    return 1;
    }
    return 0;
    }

    Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
    ---
    fs/namespace.c | 30 ++++++++++++++++++++++++------
    fs/pnode.h | 1 +
    include/linux/fs.h | 1 +
    include/linux/mount.h | 1 +
    include/linux/sched.h | 2 ++
    5 files changed, 29 insertions(+), 6 deletions(-)

    diff --git a/fs/namespace.c b/fs/namespace.c
    index a4039a3..60ca9b5 100644
    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -234,7 +234,14 @@ static struct vfsmount *clone_mnt(struct
    int flag)
    {
    struct super_block *sb = old->mnt_sb;
    - struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
    + struct vfsmount *mnt;
    +
    + if (!(old->mnt_flags & MNT_SHARE_NS)) {
    + if (old->mnt_user_ns != current->nsproxy->user_ns)
    + return ERR_PTR(-EPERM);
    + }
    +
    + mnt = alloc_vfsmnt(old->mnt_devname);

    if (mnt) {
    mnt->mnt_flags = old->mnt_flags;
    @@ -257,6 +264,10 @@ static struct vfsmount *clone_mnt(struct
    }
    if (flag & CL_MAKE_SHARED)
    set_mnt_shared(mnt);
    + if (flag & CL_SHARE_NS)
    + mnt->mnt_flags |= MNT_SHARE_NS;
    + else
    + mnt->mnt_flags &= ~MNT_SHARE_NS;

    /* stick the duplicate mount on the same expiry list
    * as the original if that was on one */
    @@ -368,6 +379,7 @@ static int show_vfsmnt(struct seq_file *
    { MNT_NOSUID, ",nosuid" },
    { MNT_NODEV, ",nodev" },
    { MNT_NOEXEC, ",noexec" },
    + { MNT_SHARE_NS, ",share_userns" },
    { MNT_NOATIME, ",noatime" },
    { MNT_NODIRATIME, ",nodiratime" },
    { MNT_RELATIME, ",relatime" },
    @@ -902,11 +914,14 @@ static int do_change_type(struct nameida
    /*
    * do loopback mount.
    */
    -static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
    +static int do_loopback(struct nameidata *nd, char *old_name, int recurse,
    + int uidns_share)
    {
    struct nameidata old_nd;
    struct vfsmount *mnt = NULL;
    int err = mount_is_safe(nd);
    + int flag = (uidns_share ? CL_SHARE_NS : 0);
    +
    if (err)
    return err;
    if (!old_name || !*old_name)
    @@ -925,9 +940,9 @@ static int do_loopback(struct nameidata

    err = -ENOMEM;
    if (recurse)
    - mnt = copy_tree(old_nd.mnt, old_nd.dentry, 0);
    + mnt = copy_tree(old_nd.mnt, old_nd.dentry, flag);
    else
    - mnt = clone_mnt(old_nd.mnt, old_nd.dentry, 0);
    + mnt = clone_mnt(old_nd.mnt, old_nd.dentry, flag);

    if (!mnt || IS_ERR(mnt)) {
    err = mnt ? PTR_ERR(mnt) : -ENOMEM;
    @@ -1414,9 +1429,11 @@ long do_mount(char *dev_name, char *dir_
    mnt_flags |= MNT_NODIRATIME;
    if (flags & MS_RELATIME)
    mnt_flags |= MNT_RELATIME;
    + if (flags & MS_SHARE_NS)
    + mnt_flags |= MNT_SHARE_NS;

    flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
    - MS_NOATIME | MS_NODIRATIME | MS_RELATIME);
    + MS_NOATIME | MS_NODIRATIME | MS_RELATIME | MS_SHARE_NS);

    /* ... and get the mountpoint */
    retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
    @@ -1431,7 +1448,8 @@ long do_mount(char *dev_name, char *dir_
    retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
    data_page);
    else if (flags & MS_BIND)
    - retval = do_loopback(&nd, dev_name, flags & MS_REC);
    + retval = do_loopback(&nd, dev_name, flags & MS_REC,
    + mnt_flags & MNT_SHARE_NS);
    else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
    retval = do_change_type(&nd, flags);
    else if (flags & MS_MOVE)
    diff --git a/fs/pnode.h b/fs/pnode.h
    index d45bd8e..eb62f4c 100644
    --- a/fs/pnode.h
    +++ b/fs/pnode.h
    @@ -22,6 +22,7 @@ #define CL_SLAVE 0x02
    #define CL_COPY_ALL 0x04
    #define CL_MAKE_SHARED 0x08
    #define CL_PROPAGATION 0x10
    +#define CL_SHARE_NS 0x20

    static inline void set_mnt_shared(struct vfsmount *mnt)
    {
    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index bed19b7..569a637 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -121,6 +121,7 @@ #define MS_PRIVATE (1<<18) /* change to
    #define MS_SLAVE (1<<19) /* change to slave */
    #define MS_SHARED (1<<20) /* change to shared */
    #define MS_RELATIME (1<<21) /* Update atime relative to mtime/ctime. */
    +#define MS_SHARE_NS (1<<22) /* ignore user namespaces for permission */
    #define MS_ACTIVE (1<<30)
    #define MS_NOUSER (1<<31)

    diff --git a/include/linux/mount.h b/include/linux/mount.h
    index e438195..00e5066 100644
    --- a/include/linux/mount.h
    +++ b/include/linux/mount.h
    @@ -35,6 +35,7 @@ #define MNT_SHRINKABLE 0x100
    #define MNT_SHARED 0x1000 /* if the vfsmount is a shared mount */
    #define MNT_UNBINDABLE 0x2000 /* if the vfsmount is a unbindable mount */
    #define MNT_PNODE_MASK 0x3000 /* propogation flag mask */
    +#define MNT_SHARE_NS 0x4000 /* ignore user namespaces for permission */

    struct vfsmount {
    struct list_head mnt_hash;
    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 450fc39..73df38c 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -1599,6 +1599,8 @@ static inline int task_mnt_same_uidns(st
    {
    if (tsk->nsproxy == init_task.nsproxy)
    return 1;
    + if (mnt->mnt_flags & MNT_SHARE_NS)
    + return 1;
    if (mnt->mnt_user_ns == tsk->nsproxy->user_ns)
    return 1;
    return 0;
    --
    1.4.1
    -
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