Messages in this thread Patch in this message | | | Subject | [RFC][PATCH] rbind across namespaces | From | Ram <> | Date | Fri, 20 May 2005 15:11:40 -0700 |
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I have enclosed a patch that allows rbinds across any two namespaces. NOTE: currenly bind from foriegn namespace to current namespace is allowed. This patch now allows:
binds/rbinds from any namespace to any other namespace, under the assumption that if a process has access to a namespace, it ought to have permission to manipulate that namespace.
The patch incorporates ideas from Miklos and Jamie, and is dependent on Miklos's 'fix race in mark_mounts_for_expiry' patch to function correctly. Also it depends on Miklos's 'fix bind mount from foreign namespace' patch, because without that patch umounts would fail.
Though we have not come up with any security reason towards why this functionality should not be allowed, I am sure it may open up some concerns.
RP
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
--- /home/linux/views/linux-2.6.12-rc4/fs/namespace.c 2005-05-06 23:22:29.000000000 -0700 +++ 2.6.12-rc4/fs/namespace.c 2005-05-20 14:44:57.000000000 -0700 @@ -616,11 +616,15 @@ out_unlock: } /* - * do loopback mount. + * do loopback mount. The loopback mount can be done from any namespace + * to any other namespace including the current namespace, as long as + * the task acquired rights to manipulate them. */ static int do_loopback(struct nameidata *nd, char *old_name, int recurse) { struct nameidata old_nd; + struct namespace *mntpt_ns = nd->mnt->mnt_namespace, *old_ns; + int mntpt_ns_flag=0, old_ns_flag=0; struct vfsmount *mnt = NULL; int err = mount_is_safe(nd); if (err) @@ -631,16 +635,54 @@ static int do_loopback(struct nameidata if (err) return err; - down_write(¤t->namespace->sem); + old_ns = old_nd.mnt->mnt_namespace; + + /* + * make sure the namespaces do not disapper while + * we operate on it + */ err = -EINVAL; - if (check_mnt(nd->mnt) && (!recurse || check_mnt(old_nd.mnt))) { - err = -ENOMEM; - if (recurse) - mnt = copy_tree(old_nd.mnt, old_nd.dentry); - else - mnt = clone_mnt(old_nd.mnt, old_nd.dentry); + if (mntpt_ns != current->namespace) { + spin_lock(&vfsmount_lock); + if (!mntpt_ns->root) { + spin_unlock(&vfsmount_lock); + goto out; + } + get_namespace(mntpt_ns); + spin_unlock(&vfsmount_lock); + mntpt_ns_flag=1; } + if (old_ns != current->namespace) { + spin_lock(&vfsmount_lock); + if (!old_ns->root) { + spin_unlock(&vfsmount_lock); + goto release_mntpt_ns; + } + get_namespace(old_ns); + spin_unlock(&vfsmount_lock); + old_ns_flag=1; + } + + /* + * make sure we don't race with some + * other thread manipulating the + * namespaces. + */ + if (old_ns < mntpt_ns) { + down_write(&old_ns->sem); + } + down_write(&mntpt_ns->sem); + if (old_ns > mntpt_ns) { + down_write(&old_ns->sem); + } + + err = -ENOMEM; + if (recurse) + mnt = copy_tree(old_nd.mnt, old_nd.dentry); + else + mnt = clone_mnt(old_nd.mnt, old_nd.dentry); + if (mnt) { /* stop bind mounts from expiring */ spin_lock(&vfsmount_lock); @@ -656,7 +698,23 @@ static int do_loopback(struct nameidata mntput(mnt); } - up_write(¤t->namespace->sem); + if (old_ns < mntpt_ns) { + up_write(&old_ns->sem); + } + up_write(&mntpt_ns->sem); + if (old_ns > mntpt_ns) { + up_write(&old_ns->sem); + } + + if (old_ns_flag) { + put_namespace(old_ns); + } + +release_mntpt_ns: + if (mntpt_ns_flag) { + put_namespace(mntpt_ns); + } +out: path_release(&old_nd); return err; } | |