make sure that mntns_install() doesn't end up with referral for root

new flag: LOOKUP_DOWN.  If the starting point is overmounted, cross
into whatever's mounted on top, triggering referrals et.al.

Use that instead of follow_down_one() loop in mntns_install(), handle
errors properly.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index 60c0a78..646db9c 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2252,6 +2252,35 @@ static inline int lookup_last(struct nameidata *nd)
        return walk_component(nd, 0);
 }
 
+static int handle_lookup_down(struct nameidata *nd)
+{
+       struct path path = nd->path;
+       struct inode *inode = nd->inode;
+       unsigned seq = nd->seq;
+       int err;
+
+       if (nd->flags & LOOKUP_RCU) {
+               /*
+                * don't bother with unlazy_walk on failure - we are
+                * at the very beginning of walk, so we lose nothing
+                * if we simply redo everything in non-RCU mode
+                */
+               if (unlikely(!__follow_mount_rcu(nd, &path, &inode, &seq)))
+                       return -ECHILD;
+       } else {
+               dget(path.dentry);
+               err = follow_managed(&path, nd);
+               if (unlikely(err < 0))
+                       return err;
+               inode = d_backing_inode(path.dentry);
+               seq = 0;
+       }
+       path_to_nameidata(&path, nd);
+       nd->inode = inode;
+       nd->seq = seq;
+       return 0;
+}
+
 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
 static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path)
 {
@@ -2260,6 +2289,15 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path
 
        if (IS_ERR(s))
                return PTR_ERR(s);
+
+       if (unlikely(flags & LOOKUP_DOWN)) {
+               err = handle_lookup_down(nd);
+               if (unlikely(err < 0)) {
+                       terminate_walk(nd);
+                       return err;
+               }
+       }
+
        while (!(err = link_path_walk(s, nd))
                && ((err = lookup_last(nd)) > 0)) {
                s = trailing_symlink(nd);

diff --git a/fs/namespace.c b/fs/namespace.c
index cc1375e..0886ef2 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3465,8 +3465,9 @@ static void mntns_put(struct ns_common *ns)
 static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 {
        struct fs_struct *fs = current->fs;
-       struct mnt_namespace *mnt_ns = to_mnt_ns(ns);
+       struct mnt_namespace *mnt_ns = to_mnt_ns(ns), *old_mnt_ns;
        struct path root;
+       int err;
 
        if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
            !ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
@@ -3477,15 +3478,18 @@ static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
                return -EINVAL;
 
        get_mnt_ns(mnt_ns);
-       put_mnt_ns(nsproxy->mnt_ns);
+       old_mnt_ns = nsproxy->mnt_ns;
        nsproxy->mnt_ns = mnt_ns;
 
        /* Find the root */
-       root.mnt    = &mnt_ns->root->mnt;
-       root.dentry = mnt_ns->root->mnt.mnt_root;
-       path_get(&root);
-       while(d_mountpoint(root.dentry) && follow_down_one(&root))
-               ;
+       err = vfs_path_lookup(mnt_ns->root->mnt.mnt_root, &mnt_ns->root->mnt,
+                               "/", LOOKUP_DOWN, &root);
+       if (err) {
+               /* revert to old namespace */
+               nsproxy->mnt_ns = old_mnt_ns;
+               put_mnt_ns(mnt_ns);
+               return err;
+       }
 
        /* Update the pwd and root */
        set_fs_pwd(fs, &root);

diff --git a/include/linux/namei.h b/include/linux/namei.h
index f29abda..8b4794e 100644 (file)
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -44,6 +44,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
 #define LOOKUP_JUMPED          0x1000
 #define LOOKUP_ROOT            0x2000
 #define LOOKUP_EMPTY           0x4000
+#define LOOKUP_DOWN            0x8000
 
 extern int path_pts(struct path *path);