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Message-ID: <20080121202306.GA5536@sergelap.austin.rr.com>
Date: Mon, 21 Jan 2008 14:23:06 -0600
From: "Serge E. Hallyn" <serue@...ibm.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: akpm@...ux-foundation.org, hch@...radead.org, serue@...ibm.com,
viro@....linux.org.uk, kzak@...hat.com,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
containers@...ts.osdl.org, util-linux-ng@...r.kernel.org
Subject: Re: [patch 09/10] unprivileged mounts: propagation: inherit owner
from parent
Quoting Miklos Szeredi (miklos@...redi.hu):
> From: Miklos Szeredi <mszeredi@...e.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@...e.cz>
As discussed many months ago this does seem like the most appropriate
behavior for propagation.
Acked-by: Serge Hallyn <serue@...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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