From 9f7d53c09a1f87ebe228b55a83c1b8f952d76260 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Wed, 8 Oct 2014 10:42:27 -0700 Subject: mnt: Prevent pivot_root from creating a loop in the mount tree commit 0d0826019e529f21c84687521d03f60cd241ca7d upstream. Andy Lutomirski recently demonstrated that when chroot is used to set the root path below the path for the new ``root'' passed to pivot_root the pivot_root system call succeeds and leaks mounts. In examining the code I see that starting with a new root that is below the current root in the mount tree will result in a loop in the mount tree after the mounts are detached and then reattached to one another. Resulting in all kinds of ugliness including a leak of that mounts involved in the leak of the mount loop. Prevent this problem by ensuring that the new mount is reachable from the current root of the mount tree. [Added stable cc. Fixes CVE-2014-7970. --Andy] Reported-by: Andy Lutomirski Reviewed-by: Andy Lutomirski Link: http://lkml.kernel.org/r/87bnpmihks.fsf@x220.int.ebiederm.org Signed-off-by: "Eric W. Biederman" Signed-off-by: Andy Lutomirski [lizf: Backported to 3.4: adjust context] Signed-off-by: Zefan Li --- fs/namespace.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index f0f2e06..f7be8d9 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2508,6 +2508,9 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, /* make sure we can reach put_old from new_root */ if (!is_path_reachable(real_mount(old.mnt), old.dentry, &new)) goto out4; + /* make certain new is below the root */ + if (!is_path_reachable(new_mnt, new.dentry, &root)) + goto out4; br_write_lock(vfsmount_lock); detach_mnt(new_mnt, &parent_path); detach_mnt(root_mnt, &root_parent); -- cgit v1.1