mnt: Prevent pivot_root from creating a loop in the mount tree

[sfrench/cifs-2.6.git] / fs / namespace.c

diff --git a/fs/namespace.c b/fs/namespace.c
index ef42d9bee2121f8e6a68937a5ecaa7670721ded9..74647c2fe69ca3703c2c1492555f5c85eb73ce72 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2820,6 +2820,9 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
        /* make sure we can reach put_old from new_root */
        if (!is_path_reachable(old_mnt, old.dentry, &new))
                goto out4;
        /* make sure we can reach put_old from new_root */
        if (!is_path_reachable(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;

        root_mp->m_count++; /* pin it so it won't go away */
        lock_mount_hash();
        detach_mnt(new_mnt, &parent_path);
        root_mp->m_count++; /* pin it so it won't go away */
        lock_mount_hash();
        detach_mnt(new_mnt, &parent_path);