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    SubjectRe: [patch 09/10] unprivileged mounts: propagation: inherit owner from parent
    Quoting Miklos Szeredi (miklos@szeredi.hu):
    > From: Miklos Szeredi <mszeredi@suse.cz>
    >
    > On mount propagation, let the owner of the clone be inherited from the
    > parent into which it has been propagated.
    >
    > If the parent has the "nosuid" flag, set this flag for the child as
    > well. This is needed for the suid-less namespace (use case #2 in the
    > first patch header), where all mounts are owned by the user and have
    > the nosuid flag set. In this case the propagated mount needs to have
    > nosuid, otherwise a suid executable may be misused by the user.
    >
    > Similar treatment is not needed for "nodev", because devices can't be
    > abused this way: the user is not able to gain privileges to devices by
    > rearranging the mount namespace.
    >
    > Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

    As discussed many months ago this does seem like the most appropriate
    behavior for propagation.

    Acked-by: Serge Hallyn <serue@us.ibm.com>

    > ---
    >
    > Index: linux/fs/namespace.c
    > ===================================================================
    > --- linux.orig/fs/namespace.c 2008-01-16 13:25:09.000000000 +0100
    > +++ linux/fs/namespace.c 2008-01-16 13:25:11.000000000 +0100
    > @@ -506,10 +506,10 @@ static int reserve_user_mount(void)
    > return err;
    > }
    >
    > -static void __set_mnt_user(struct vfsmount *mnt)
    > +static void __set_mnt_user(struct vfsmount *mnt, uid_t owner)
    > {
    > WARN_ON(mnt->mnt_flags & MNT_USER);
    > - mnt->mnt_uid = current->fsuid;
    > + mnt->mnt_uid = owner;
    > mnt->mnt_flags |= MNT_USER;
    >
    > if (!capable(CAP_SETUID))
    > @@ -520,7 +520,7 @@ static void __set_mnt_user(struct vfsmou
    >
    > static void set_mnt_user(struct vfsmount *mnt)
    > {
    > - __set_mnt_user(mnt);
    > + __set_mnt_user(mnt, current->fsuid);
    > spin_lock(&vfsmount_lock);
    > nr_user_mounts++;
    > spin_unlock(&vfsmount_lock);
    > @@ -536,7 +536,7 @@ static void clear_mnt_user(struct vfsmou
    > }
    >
    > static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
    > - int flag)
    > + int flag, uid_t owner)
    > {
    > struct super_block *sb = old->mnt_sb;
    > struct vfsmount *mnt;
    > @@ -560,7 +560,10 @@ static struct vfsmount *clone_mnt(struct
    > /* don't copy the MNT_USER flag */
    > mnt->mnt_flags &= ~MNT_USER;
    > if (flag & CL_SETUSER)
    > - __set_mnt_user(mnt);
    > + __set_mnt_user(mnt, owner);
    > +
    > + if (flag & CL_NOSUID)
    > + mnt->mnt_flags |= MNT_NOSUID;
    >
    > if (flag & CL_SLAVE) {
    > list_add(&mnt->mnt_slave, &old->mnt_slave_list);
    > @@ -1066,7 +1069,7 @@ static int lives_below_in_same_fs(struct
    > }
    >
    > struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
    > - int flag)
    > + int flag, uid_t owner)
    > {
    > struct vfsmount *res, *p, *q, *r, *s;
    > struct nameidata nd;
    > @@ -1074,7 +1077,7 @@ struct vfsmount *copy_tree(struct vfsmou
    > if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
    > return ERR_PTR(-EPERM);
    >
    > - res = q = clone_mnt(mnt, dentry, flag);
    > + res = q = clone_mnt(mnt, dentry, flag, owner);
    > if (IS_ERR(q))
    > goto error;
    > q->mnt_mountpoint = mnt->mnt_mountpoint;
    > @@ -1096,7 +1099,7 @@ struct vfsmount *copy_tree(struct vfsmou
    > p = s;
    > nd.path.mnt = q;
    > nd.path.dentry = p->mnt_mountpoint;
    > - q = clone_mnt(p, p->mnt_root, flag);
    > + q = clone_mnt(p, p->mnt_root, flag, owner);
    > if (IS_ERR(q))
    > goto error;
    > spin_lock(&vfsmount_lock);
    > @@ -1121,7 +1124,7 @@ struct vfsmount *collect_mounts(struct v
    > {
    > struct vfsmount *tree;
    > down_read(&namespace_sem);
    > - tree = copy_tree(mnt, dentry, CL_COPY_ALL | CL_PRIVATE);
    > + tree = copy_tree(mnt, dentry, CL_COPY_ALL | CL_PRIVATE, 0);
    > up_read(&namespace_sem);
    > return tree;
    > }
    > @@ -1292,7 +1295,8 @@ static int do_change_type(struct nameida
    > */
    > static int do_loopback(struct nameidata *nd, char *old_name, int flags)
    > {
    > - int clone_fl;
    > + int clone_fl = 0;
    > + uid_t owner = 0;
    > struct nameidata old_nd;
    > struct vfsmount *mnt = NULL;
    > int err;
    > @@ -1313,11 +1317,17 @@ static int do_loopback(struct nameidata
    > if (!check_mnt(nd->path.mnt) || !check_mnt(old_nd.path.mnt))
    > goto out;
    >
    > - clone_fl = (flags & MS_SETUSER) ? CL_SETUSER : 0;
    > + if (flags & MS_SETUSER) {
    > + clone_fl |= CL_SETUSER;
    > + owner = current->fsuid;
    > + }
    > +
    > if (flags & MS_REC)
    > - mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
    > + mnt = copy_tree(old_nd.path.mnt, old_nd.path.dentry, clone_fl,
    > + owner);
    > else
    > - mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl);
    > + mnt = clone_mnt(old_nd.path.mnt, old_nd.path.dentry, clone_fl,
    > + owner);
    >
    > err = PTR_ERR(mnt);
    > if (IS_ERR(mnt))
    > @@ -1541,7 +1551,7 @@ static int do_new_mount(struct nameidata
    > }
    >
    > if (flags & MS_SETUSER)
    > - __set_mnt_user(mnt);
    > + __set_mnt_user(mnt, current->fsuid);
    >
    > return do_add_mount(mnt, nd, mnt_flags, NULL);
    >
    > @@ -1937,7 +1947,7 @@ static struct mnt_namespace *dup_mnt_ns(
    > down_write(&namespace_sem);
    > /* First pass: copy the tree topology */
    > new_ns->root = copy_tree(mnt_ns->root, mnt_ns->root->mnt_root,
    > - CL_COPY_ALL | CL_EXPIRE);
    > + CL_COPY_ALL | CL_EXPIRE, 0);
    > if (IS_ERR(new_ns->root)) {
    > up_write(&namespace_sem);
    > kfree(new_ns);
    > Index: linux/fs/pnode.c
    > ===================================================================
    > --- linux.orig/fs/pnode.c 2008-01-16 13:25:07.000000000 +0100
    > +++ linux/fs/pnode.c 2008-01-16 13:25:11.000000000 +0100
    > @@ -181,15 +181,28 @@ int propagate_mnt(struct vfsmount *dest_
    >
    > for (m = propagation_next(dest_mnt, dest_mnt); m;
    > m = propagation_next(m, dest_mnt)) {
    > - int type;
    > + int clflags;
    > + uid_t owner = 0;
    > struct vfsmount *source;
    >
    > if (IS_MNT_NEW(m))
    > continue;
    >
    > - source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
    > + source = get_source(m, prev_dest_mnt, prev_src_mnt, &clflags);
    >
    > - child = copy_tree(source, source->mnt_root, type);
    > + if (m->mnt_flags & MNT_USER) {
    > + clflags |= CL_SETUSER;
    > + owner = m->mnt_uid;
    > +
    > + /*
    > + * If propagating into a user mount which doesn't
    > + * allow suid, then make sure, the child(ren) won't
    > + * allow suid either
    > + */
    > + if (m->mnt_flags & MNT_NOSUID)
    > + clflags |= CL_NOSUID;
    > + }
    > + child = copy_tree(source, source->mnt_root, clflags, owner);
    > if (IS_ERR(child)) {
    > ret = PTR_ERR(child);
    > list_splice(tree_list, tmp_list.prev);
    > Index: linux/fs/pnode.h
    > ===================================================================
    > --- linux.orig/fs/pnode.h 2008-01-16 13:25:05.000000000 +0100
    > +++ linux/fs/pnode.h 2008-01-16 13:25:11.000000000 +0100
    > @@ -24,6 +24,7 @@
    > #define CL_PROPAGATION 0x10
    > #define CL_PRIVATE 0x20
    > #define CL_SETUSER 0x40
    > +#define CL_NOSUID 0x80
    >
    > static inline void set_mnt_shared(struct vfsmount *mnt)
    > {
    > @@ -36,4 +37,6 @@ int propagate_mnt(struct vfsmount *, str
    > struct list_head *);
    > int propagate_umount(struct list_head *);
    > int propagate_mount_busy(struct vfsmount *, int);
    > +struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int, uid_t);
    > +
    > #endif /* _LINUX_PNODE_H */
    > Index: linux/include/linux/fs.h
    > ===================================================================
    > --- linux.orig/include/linux/fs.h 2008-01-16 13:25:09.000000000 +0100
    > +++ linux/include/linux/fs.h 2008-01-16 13:25:11.000000000 +0100
    > @@ -1493,7 +1493,6 @@ extern int may_umount(struct vfsmount *)
    > extern void umount_tree(struct vfsmount *, int, struct list_head *);
    > extern void release_mounts(struct list_head *);
    > extern long do_mount(char *, char *, char *, unsigned long, void *);
    > -extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
    > extern void mnt_set_mountpoint(struct vfsmount *, struct dentry *,
    > struct vfsmount *);
    > extern struct vfsmount *collect_mounts(struct vfsmount *, struct dentry *);
    >
    > --
    > -
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