LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: "Serge E. Hallyn" <serue@us.ibm.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: akpm@linux-foundation.org, hch@infradead.org, serue@us.ibm.com,
	viro@ftp.linux.org.uk, kzak@redhat.com,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	containers@lists.osdl.org, util-linux-ng@vger.kernel.org
Subject: Re: [patch 09/10] unprivileged mounts: propagation: inherit owner from parent
Date: Mon, 21 Jan 2008 14:23:06 -0600	[thread overview]
Message-ID: <20080121202306.GA5536@sergelap.austin.rr.com> (raw)
In-Reply-To: <20080116123436.411935940@szeredi.hu>

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 *);
> 
> --
> -
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

  reply	other threads:[~2008-01-21 21:26 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-16 12:31 [patch 00/10] mount ownership and unprivileged mount syscall (v7) Miklos Szeredi
2008-01-16 12:31 ` [patch 01/10] unprivileged mounts: add user mounts to the kernel Miklos Szeredi
2008-01-16 12:31 ` [patch 02/10] unprivileged mounts: allow unprivileged umount Miklos Szeredi
2008-01-16 12:31 ` [patch 03/10] unprivileged mounts: propagate error values from clone_mnt Miklos Szeredi
2008-01-16 12:31 ` [patch 04/10] unprivileged mounts: account user mounts Miklos Szeredi
2008-01-16 12:31 ` [patch 05/10] unprivileged mounts: allow unprivileged bind mounts Miklos Szeredi
2008-01-16 12:31 ` [patch 06/10] unprivileged mounts: allow unprivileged mounts Miklos Szeredi
2008-01-16 12:31 ` [patch 07/10] unprivileged mounts: add sysctl tunable for "safe" property Miklos Szeredi
2008-01-21 20:32   ` Serge E. Hallyn
2008-01-21 21:37     ` Miklos Szeredi
2008-01-22 20:48       ` Serge E. Hallyn
2008-01-22 22:59         ` Miklos Szeredi
2008-01-23  0:00           ` Serge E. Hallyn
2008-01-16 12:31 ` [patch 08/10] unprivileged mounts: make fuse safe Miklos Szeredi
2008-01-21 20:41   ` Serge E. Hallyn
2008-01-16 12:31 ` [patch 09/10] unprivileged mounts: propagation: inherit owner from parent Miklos Szeredi
2008-01-21 20:23   ` Serge E. Hallyn [this message]
2008-01-16 12:31 ` [patch 10/10] unprivileged mounts: add "no submounts" flag Miklos Szeredi
  -- strict thread matches above, loose matches on Subject: below --
2008-02-05 21:36 [patch 00/10] mount ownership and unprivileged mount syscall (v8) Miklos Szeredi
2008-02-05 21:36 ` [patch 09/10] unprivileged mounts: propagation: inherit owner from parent Miklos Szeredi
2007-04-27 12:04 [patch 00/10] mount ownership and unprivileged mount syscall (v5) Miklos Szeredi
2007-04-27 12:04 ` [patch 09/10] unprivileged mounts: propagation: inherit owner from parent Miklos Szeredi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20080121202306.GA5536@sergelap.austin.rr.com \
    --to=serue@us.ibm.com \
    --cc=akpm@linux-foundation.org \
    --cc=containers@lists.osdl.org \
    --cc=hch@infradead.org \
    --cc=kzak@redhat.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=miklos@szeredi.hu \
    --cc=util-linux-ng@vger.kernel.org \
    --cc=viro@ftp.linux.org.uk \
    --subject='Re: [patch 09/10] unprivileged mounts: propagation: inherit owner from parent' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).