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mnt: Refactor the logic for mounting sysfs and proc in a user namespace
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. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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@ -2332,6 +2332,8 @@ unlock:
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return err;
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}
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static bool fs_fully_visible(struct file_system_type *fs_type);
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/*
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* create a new mount for userspace and request it to be added into the
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* namespace's tree
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@ -2363,6 +2365,10 @@ static int do_new_mount(struct path *path, const char *fstype, int flags,
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flags |= MS_NODEV;
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mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;
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}
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if (type->fs_flags & FS_USERNS_VISIBLE) {
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if (!fs_fully_visible(type))
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return -EPERM;
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}
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}
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mnt = vfs_kern_mount(type, flags, name, data);
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@ -3164,7 +3170,7 @@ bool current_chrooted(void)
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return chrooted;
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}
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bool fs_fully_visible(struct file_system_type *type)
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static bool fs_fully_visible(struct file_system_type *type)
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{
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struct mnt_namespace *ns = current->nsproxy->mnt_ns;
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struct mount *mnt;
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@ -112,9 +112,6 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
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ns = task_active_pid_ns(current);
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options = data;
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if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
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return ERR_PTR(-EPERM);
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/* Does the mounter have privilege over the pid namespace? */
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if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
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return ERR_PTR(-EPERM);
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@ -159,7 +156,7 @@ static struct file_system_type proc_fs_type = {
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.name = "proc",
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.mount = proc_mount,
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.kill_sb = proc_kill_sb,
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.fs_flags = FS_USERNS_MOUNT,
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.fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
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};
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void __init proc_root_init(void)
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@ -31,9 +31,6 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
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bool new_sb;
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if (!(flags & MS_KERNMOUNT)) {
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if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
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return ERR_PTR(-EPERM);
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if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
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return ERR_PTR(-EPERM);
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}
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@ -58,7 +55,7 @@ static struct file_system_type sysfs_fs_type = {
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.name = "sysfs",
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.mount = sysfs_mount,
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.kill_sb = sysfs_kill_sb,
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.fs_flags = FS_USERNS_MOUNT,
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.fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
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};
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int __init sysfs_init(void)
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@ -1897,6 +1897,7 @@ struct file_system_type {
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#define FS_HAS_SUBTYPE 4
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#define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
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#define FS_USERNS_DEV_MOUNT 16 /* A userns mount does not imply MNT_NODEV */
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#define FS_USERNS_VISIBLE 32 /* FS must already be visible */
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#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
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struct dentry *(*mount) (struct file_system_type *, int,
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const char *, void *);
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@ -1984,7 +1985,6 @@ extern int vfs_ustat(dev_t, struct kstatfs *);
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extern int freeze_super(struct super_block *super);
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extern int thaw_super(struct super_block *super);
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extern bool our_mnt(struct vfsmount *mnt);
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extern bool fs_fully_visible(struct file_system_type *);
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extern int current_umask(void);
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