Merge branch 'work.sane_pwd' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull misc vfs updates from Al Viro:
 "Making sure that something like a referral point won't end up as pwd
  or root.

  The main part is the last commit (fixing mntns_install()); that one
  fixes a hard-to-hit race. The fchdir() commit is making fchdir(2) a
  bit more robust - it should be impossible to get opened files (even
  O_PATH ones) for referral points in the first place, so the existing
  checks are OK, but checking the same thing as in chdir(2) is just as
  cheap.

  The path_init() commit removes a redundant check that shouldn't have
  been there in the first place"

* 'work.sane_pwd' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  make sure that mntns_install() doesn't end up with referral for root
  path_init(): don't bother with checking MAY_EXEC for LOOKUP_ROOT
  make sure that fchdir() won't accept referral points, etc.

1 files changed, 11 insertions, 7 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index b3b115b..8bd3e4d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3462,8 +3462,9 @@ 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) ||
@@ -3474,15 +3475,18 @@ 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);